Lennox Merit® Series ML17XC1 Units - Installation Instructions

General

This ML17XC1 outdoor air conditioner with an all-aluminum coil is designed for use with HFC-410A refrigerant only. It must be installed with an approved indoor air handler or coil. For AHRI Certified system match-ups and expanded ratings, visit www.LennoxPros.com.

These instructions are intended as a general guide and do not supersede local codes. Consult authorities having jurisdiction before installation.

NOTICE! Charging information is provided on the charging procedure sticker on the unit access panel. For more in-depth information, consult the Installation and Service Procedures manual on LennoxPros.com or contact the Technical Support department at 800-453-6669.

⚠️ WARNING Improper installation, adjustment, alteration, service, or maintenance can cause property damage, personal injury, or loss of life. Installation and service must be performed by a licensed professional HVAC installer or equivalent, or service agency.

⚠️ CAUTION As with any mechanical equipment, contact with sharp sheet metal edges can result in personal injury. Take care while handling this equipment and wear gloves and protective clothing.

ℹ️ IMPORTANT Special procedures are required for cleaning the all-aluminum coil in this unit. See page 15 for information.

STEP 1 – SETTING THE UNIT – Clearances

Figure 1: Diagram showing required clearances around an outdoor air conditioner unit. Labels indicate areas for 'See NOTES' and a 'CONTROL BOX'.

NOTES:

• Service clearance of 30 in. (762 mm) must be maintained on one of the sides adjacent to the control box.
• Clearance to one of the other three sides must be 36 in. (914 mm).
• Clearance to one of the remaining two sides may be 12 in. (305 mm) and the final side may be 6 in. (152 mm).
• A clearance of 24 in. must be maintained between two units.
• 48 in. (1219 mm) clearance required on top of unit.

NOTICE: Specific applications may require adjustment of the listed installation clearances to provide protection for the unit from physical damage or to avoid conditions which limit operating efficiency. For example, clearances may need to be increased to prevent snow or ice from falling on the top of the unit, or to prevent air recirculation when the unit is installed under a deck or in another tight space.

Unit Dimensions

Figure 2: Side view diagram illustrating the unit dimensions labeled A and B.

Table 1: Unit Dimensions

STEP 1 – SETTING THE UNIT (Continued) – Unit Placement

⚠️ CAUTION Before attempting to perform any service or maintenance, turn the electrical power to the unit OFF at the disconnect switch.

⚠️ WARNING To prevent personal injury, as well as damage to panels, unit, or structure, observe the following: While installing or servicing this unit, carefully stow all removed panels so that they do not cause injury to personnel, objects, or nearby structures. Also, take care to store panels where they will not be subject to damage (e.g., being bent or scratched). Consider any weather conditions (especially wind) that may cause panels to be blown around and damaged.

NOTICE! Roof Damage! This system contains both refrigerant and oil. Some rubber roofing material may absorb oil, causing the rubber to degrade. Failure to follow this notice could result in damage to the roof surface.

ℹ️ IMPORTANT This unit must be matched with an indoor coil as specified by AHRI. For AHRI Certified system match-ups and expanded ratings, visit www.LennoxPros.com. Coils previously charged with HCFC-22 must be flushed.

ℹ️ IMPORTANT Exhaust vents from dryers, water heaters, and furnaces should be directed away from the outdoor unit. Prolonged exposure to exhaust gases and the chemicals contained within them may cause condensation to form on the steel cabinet and other metal components of the outdoor unit, diminishing unit performance and longevity.

PLACEMENT: Install unit away from windows.

Figure 3: Diagram showing unit placement away from windows. It illustrates two 90° elbows installed in the line set to reduce line set vibration.

SLAB MOUNTING: Install unit level or, if on a slope, maintain a slope tolerance of 2 degrees (or 2 inches per 5 feet [50 mm per 1.5 m]) away from the building structure.

Figure 4: Diagram illustrating slab mounting for the outdoor unit, showing the unit on a mounting slab which is level or sloped away from the building structure.

STEP 2 – REFRIGERANT PIPING – Flushing Existing Line Set & Indoor Coil

⚠️ WARNING Refrigerant can be harmful if inhaled. Refrigerant must be used and recovered responsibly. Failure to follow this warning may result in personal injury or death.

ℹ️ IMPORTANT If this unit is being matched with an approved line set or indoor unit coil that was previously charged with mineral oil, or if it is being matched with a coil manufactured before January 1999, the coil and line set must be flushed prior to installation. Take care to empty all existing traps. Polyvinyl ether (PVE) oils are used in Lennox variable-capacity units charged with HFC-410A refrigerant. Residual mineral oil can act as an insulator, preventing proper heat transfer, and can clog the expansion device, reducing system performance and capacity. Failure to properly flush the system per these instructions and the detailed Installation and Service Procedures manual will void the warranty.

Flush the existing line set per the following instructions. For more information, refer to the Installation and Service Procedures manual available on LennoxPros.com.

⚠️ CAUTION DO NOT attempt to flush and re-use existing line sets or indoor coil when the system contains contaminants (i.e., compressor burn out).

If a new line set is being installed, size the piping per Table 2.

⚠️ WARNING When using a high-pressure gas such as nitrogen to pressurize a refrigeration or air conditioning system, use a regulator that can control the pressure down to 1 or 2 psig (6.9 to 13.8 kPa).

⚠️ WARNING Polyol ester (POE) oils used with HFC-410A refrigerant absorb moisture very quickly. It is very important that the refrigerant system be kept closed as much as possible. DO NOT remove line set caps or service valve stub caps until you are ready to make connections.

⚠️ WARNING Fire, Explosion, and Personal Safety hazard. Failure to follow this warning could result in damage, personal injury, or death. Never use oxygen to pressurize or purge refrigeration lines. Oxygen, when exposed to a spark or open flame, can cause fire and/or an explosion, that could result in property damage, personal injury, or death.

LIQUID LINE FILTER DRIER INSTALLATION: The provided filter drier must be field installed in the liquid line between the outdoor unit's liquid line service valve and the indoor coil's metering device (fixed orifice or TXV) as illustrated in Figure 5. This filter drier must be installed to ensure a clean, moisture-free system. Failure to install the filter drier will void the warranty. A replacement filter drier is available from Lennox. See Brazing Connections on page 6 for special procedures on brazing filter drier connections to the liquid line.

Figure 5: Diagram showing the typical installation location of a liquid line filter drier in the refrigerant line between the outdoor unit's liquid line service valve and the indoor coil's metering device.

Table 2: Refrigerant Line Set – Inches (MM)

* Some applications may require a field-provided 1-1/8" to 7/8" adapter.

NOTE: When installing refrigerant lines longer than 50 feet, refer to the Refrigerant Piping Design and Fabrication Guidelines manual available on LennoxPros.com (Corp. 9351-L9), or contact the Technical Support Department Product Application group for assistance.

NOTE: For new or replacement line set installation, refer to Service and Application Note - Corp. 9112-L4 (C-91-4).

LINE SET INSTALLATION

ℹ️ IMPORTANT – Refrigerant lines must not contact structure.

Line Set Isolation: The following illustrations are examples of proper refrigerant line set isolation:

REFRIGERANT LINE SET – TRANSITION FROM VERTICAL TO HORIZONTAL

Diagram showing a refrigerant line set transitioning from vertical to horizontal, using anchored heavy nylon wire ties or automotive muffler-type hangers for support and isolation from the wall stud.

REFRIGERANT LINE SET – INSTALLING VERTICAL RUNS (NEW CONSTRUCTION SHOWN)

ℹ️ IMPORTANT – Refrigerant lines must not contact wall.

NOTE: Insulate liquid line when it is routed through areas where the surrounding ambient temperature could become higher than the temperature of the liquid line or when pressure drop is equal to or greater than 20 psig.

Diagram showing vertical refrigerant line set installation, with insulation on the liquid line and non-corrosive metal sleeves for support. It includes labels for outside wall, wall stud, wood block, wire tie, strap, liquid line, and suction line wrapped in Armaflex.

REFRIGERANT LINE SET – INSTALLING HORIZONTAL RUNS

To hang line set from joist or rafter, use either metal strapping material or anchored heavy nylon wire ties.

Diagram illustrating horizontal refrigerant line set installation, showing strapping material around the suction line only, attached to a floor joist or roof rafter at 8-foot intervals. The liquid line is then strapped to the suction line. It also shows a non-corrosive metal sleeve and tape or wire tie.

NOTE: Similar installation practices should be used if the line set is to be installed on the exterior of an outside wall.

STEP 2 – REFRIGERANT PIPING – Removing Existing Indoor Metering Device

1A: TYPICAL EXISTING FIXED ORIFICE REMOVAL PROCEDURE (UNCASED COIL SHOWN)

Diagrams illustrating the removal of a fixed orifice metering device from an indoor coil, showing distributor tubes, liquid line orifice housing, Teflon® ring, and brass nut.

Steps for removal:

1. On fully cased coils, remove the coil access and plumbing panels.
2. Remove any shipping clamps from the liquid line and distributor assembly.
3. Using two wrenches, disconnect the liquid line from the liquid line orifice housing. Take care not to twist or damage distributor tubes during this process.
4. Remove and discard the fixed orifice, valve stem assembly (if present), and Teflon® washer.
5. Use a field-provided fitting to temporarily reconnect the liquid line to the indoor unit's liquid line orifice housing.

1B: TYPICAL EXISTING EXPANSION VALVE REMOVAL PROCEDURE (UNCASED COIL SHOWN)

Diagrams illustrating the removal of an expansion valve metering device from an indoor coil, showing two-piece patch plate, distributor tubes, stub end, liquid line orifice housing, check expansion valve, Teflon® ring, sensing line, equalizer line, and liquid line assembly with brass nut.

Steps for removal:

1. On fully cased coils, remove the coil access and plumbing panels.
2. Remove any shipping clamps from the liquid line and distributor assembly.
3. Disconnect the equalizer line from the check expansion valve equalizer line fitting on the vapor line.
4. Remove the vapor line sensing bulb.
5. Disconnect the liquid line from the check expansion valve at the liquid line assembly.
6. Disconnect the check expansion valve from the liquid line orifice housing. Take care not to twist or damage distributor tubes during this process.
7. Remove and discard the check expansion valve and the two Teflon® rings.
8. Use a field-provided fitting to temporarily reconnect the liquid line to the indoor unit's liquid line orifice housing.

2: CONNECT GAUGES AND EQUIPMENT FOR FLUSHING PROCEDURE

Diagram showing the setup for flushing the existing line set and indoor coil. It includes a cylinder containing clean HCFC-22, a gauge manifold, a new outdoor unit, an existing indoor unit, a liquid line service valve, and a recovery machine with a recovery cylinder.

Connections:

• A - HCFC-22 cylinder with clean refrigerant (positioned to deliver liquid refrigerant) to the vapor service valve.
• B - HCFC-22 gauge set (low side) to the liquid line valve.
• C - HCFC-22 gauge set center port to the inlet on the recovery machine with an empty recovery tank connected to the gauge set.
• D - Connect recovery tank to recovery machine per machine instructions.

3: FLUSHING LINE SET

The line set and indoor unit coil must be flushed with at least the same amount of clean refrigerant that previously charged the system. Check the charge in the flushing cylinder before proceeding.

1. Set the recovery machine for liquid recovery and start it. Open the gauge set valves to allow the recovery machine to pull a vacuum on the existing system line set and indoor unit coil.
2. Position the cylinder of clean HCFC-22 for delivery of liquid refrigerant and open its valve to allow liquid refrigerant to flow into the system through the vapor line valve. Allow the refrigerant to pass from the cylinder and through the line set and the indoor unit coil before it enters the recovery machine.
3. After all liquid refrigerant has been recovered, switch the recovery machine to vapor recovery to recover all HCFC-22 vapor. Allow the recovery machine to pull the system down to 0.
4. Close the valve on the inverted HCFC-22 drum and the gauge set valves. Pump the remaining refrigerant out of the recovery machine and turn the machine off.

STEP 2 – REFRIGERANT PIPING – Brazing Procedures

1: CUT AND DEBUR

Cut ends of the refrigerant lines square (free from nicks or dents) and debur the ends. The pipe must remain round. Do not crimp the end of the line.

Diagram showing how to cut and debur refrigerant lines, illustrating line set size matching service valve connection and when the line set size is smaller than the connection.

2: CAP AND CORE REMOVAL

Remove service cap and core from both the vapor and liquid line service ports.

Diagram showing service port caps and cores for liquid and vapor line service valves.

3: ATTACH THE MANIFOLD GAUGE SET FOR BRAZING LIQUID AND VAPOR LINE SERVICE VALVES

Flow regulated nitrogen (at 1 to 2 psig) through the low-side refrigeration gauge set into the liquid line service port valve, and out of the vapor line service port valve.

Steps:

• A - Connect gauge set low pressure side to the liquid line service valve (service port).
• B - Connect gauge set center port to bottle of nitrogen with regulator.
• C - Remove core from valve in vapor line service port to allow nitrogen to escape.

Figure 8: Diagram showing the setup for brazing line sets, including manifold gauge connections, nitrogen cylinder, and outdoor/indoor units. It indicates pointing the flame away from the service valve when brazing.

CAUTION Brazing alloys and flux contain materials hazardous to your health. Avoid breathing vapors or fumes from brazing operations. Perform operations only in well-ventilated areas. Wear gloves and protective goggles or face shield to protect against burns. Wash hands with soap and water after handling brazing alloys and flux.

⚠️ WARNING Danger of fire. Bleeding the refrigerant charge from only the high side may result in pressurization of the low side shell and suction tubing. Application of a brazing torch to a pressurized system may result in ignition of the refrigerant and oil mixture. Check the high and low pressures before applying heat.

4: WRAP SERVICE VALVES

To help protect service valve seals during brazing, wrap water-saturated cloths around service valve bodies and copper tube stubs. Use additional water-saturated cloths underneath the valve body to protect the base paint.

5: FLOW NITROGEN

Flow regulated nitrogen (at 1 to 2 psig) through the refrigeration gauge set into the valve stem port connection on the liquid service valve and out of the vapor valve stem port. See steps 3A, 3B, and 3C for manifold gauge set connections.

6: BRAZE LINE SET

Wrap both service valves with water-saturated cloths as illustrated and mentioned in step 4, before brazing to the line set. Cloths must remain water-saturated throughout the brazing and cool-down process.

Diagram showing water-saturated cloths wrapped around service valves and copper tube stubs during brazing.

ℹ️ IMPORTANT Allow braze joint to cool. Apply additional water-saturated cloths to help cool the brazed joint. Do not remove water-saturated cloths until piping has cooled. Temperatures above 250°F will damage valve seals.

⚠️ WARNING FIRE, PERSONAL INJURY, OR PROPERTY DAMAGE may result if you do not wrap a water-saturated cloth around both liquid and suction line service valve bodies and copper tube stub while brazing the line set! The braze, when complete, must be quenched with water to absorb any residual heat. Do not open service valves until refrigerant lines and indoor coil have been leak-tested and evacuated. Refer to Installation and Service Procedures manual found on LennoxPros.com.

7: PREPARATION FOR NEXT STEP

After all connections have been brazed, disconnect manifold gauge set from service ports. Apply additional water-saturated cloths to both service valves to cool piping. Once piping is cool, remove all water-saturated cloths.

STEP 2 – REFRIGERANT PIPING – Install Indoor Expansion Valve

This outdoor unit is designed for systems using either a fixed orifice (RFC) (included with outdoor unit) or an expansion valve metering device (purchased separately) at the indoor coil. See the ML17XC1 Product Specifications bulletin (EHB) for approved expansion valve kit match-ups. The expansion valve unit can be installed internal or external to the indoor coil. In applications where an uncased coil is being installed in a field-provided plenum, install the expansion valve in a manner that will provide access for field servicing. Refer to the illustration for reference during installation.

INDOOR EXPANSION VALVE INSTALLATION (Uncased Coil Shown)

Diagrams and steps for installing the check expansion valve, including attaching it to the liquid line orifice housing, lubricating threads, and connecting the liquid line assembly. It also details sensing bulb installation and equalizer line installation.

SENSING BULB INSTALLATION:

• Attach the vapor line sensing bulb in the proper orientation using the clamp and screws provided.
• NOTE: It is preferred to have the sensing bulb installed on a horizontal run of the vapor line, but installation on a vertical run is acceptable if necessary.
• NOTE: Confirm proper thermal contact between the vapor line and the check/expansion bulb before insulating the sensing bulb.

EQUALIZER LINE INSTALLATION:

• Remove and discard the flare seal cap or flare nut with copper flare seal bonnet from the equalizer line port on the vapor line.
• Remove the field-provided fitting that temporarily reconnected the liquid line to the indoor unit's distributor assembly.
• Connect the equalizer line from the check expansion valve to the equalizer vapor port on the vapor line. Finger tighten the flare nut plus 1/8 turn (7 ft-lbs).

STEP 3 – LEAK TEST AND EVACUATION

LEAK TEST

Figure 10: Diagram showing the gauge set connection for leak testing the system with HFC-410A refrigerant and nitrogen. It shows connections to the outdoor unit's vapor service valve and liquid line service valve.

1: CONNECT GAUGE SET

• A - Connect the high-pressure hose of an HFC-410A manifold gauge set to the vapor valve service port. NOTE: Normally, the high-pressure hose is connected to the liquid line port, but connecting it to the vapor port better protects the manifold gauge set from high-pressure damage.
• B - With both manifold valves closed, connect the cylinder of HFC-410A refrigerant to the center port of the manifold gauge set. NOTE: Later, the HFC-410A container will be replaced by the nitrogen container.

2: TEST FOR LEAKS

After the line set has been connected to the indoor and outdoor units, check the line set connections and indoor unit for leaks using the following procedure:

• A - With both manifold valves closed, connect the cylinder of HFC-410A refrigerant to the center port of the manifold gauge set. Open the valve on the HFC-410A cylinder (vapor only).
• B - Open the high-pressure side of the manifold to allow HFC-410A into the line set and indoor unit. Weigh in a trace amount of HFC-410A. [A trace amount is a maximum of two ounces (57 g) refrigerant or three pounds (31 kPa) pressure.] Close the valve on the HFC-410A cylinder and the valve on the high-pressure side of the manifold gauge set. Disconnect the HFC-410A cylinder.
• C - Connect a cylinder of nitrogen with a pressure-regulating valve to the center port of the manifold gauge set.
• D - Adjust nitrogen pressure to 150 psig (1034 kPa). Open the valve on the high side of the manifold gauge set to pressurize the line set and the indoor unit.
• E - After a few minutes, open one of the service valve ports and verify that the refrigerant added to the system earlier is measurable with a leak detector.
• F - After leak testing, disconnect gauges from service ports.

STEP 3 – LEAK TEST AND EVACUATION (Continued)

3: CONNECT GAUGE SET (EVACUATION)

Figure 11: Diagram illustrating the gauge set connection for system evacuation using a vacuum pump and micron gauge. It shows connections to the outdoor unit's vapor and liquid line service valves, and the vacuum pump.

NOTE: Remove cores from service valves (if not already done).

• A - Connect the low side of the manifold gauge set with a 1/4 SAE in-line tee to the vapor line service valve.
• B - Connect the high side of the manifold gauge set to the liquid line service valve.
• C - Connect the available micron gauge connector on the 1/4 SAE in-line tee.
• D - Connect the vacuum pump (with vacuum gauge) to the center port of the manifold gauge set. The center port line will be used later for both the HFC-410A and nitrogen containers.

4: EVACUATE THE SYSTEM

• A - Open both manifold valves and start the vacuum pump.
• B - Evacuate the line set and indoor unit to an absolute pressure of 23,000 microns (29.01 inches of mercury).

NOTE: During the early stages of evacuation, it is desirable to close the manifold gauge valve at least once. A rapid rise in pressure indicates a relatively large leak. If this occurs, repeat the leak testing procedure.

NOTE: The term 'absolute pressure' means the total actual pressure above absolute zero within a given volume or system. Absolute pressure in a vacuum is equal to atmospheric pressure minus vacuum pressure.

• C - When the absolute pressure reaches 23,000 microns (29.01 inches of mercury), perform the following:
  • Close manifold gauge valves.
  • Close valve on vacuum pump.
  • Turn off vacuum pump.
  • Disconnect manifold gauge center port hose from vacuum pump.
  • Attach manifold center port hose to a nitrogen cylinder with pressure regulator set to 150 psig (1034 kPa) and purge the hose.
  • Open manifold gauge valves to break the vacuum in the line set and indoor unit.
  • Close manifold gauge valves.
• D - Shut off the nitrogen cylinder and remove the manifold gauge hose from the cylinder. Open the manifold gauge valves to release the nitrogen from the line set and indoor unit.
• E - Reconnect the manifold gauge to the vacuum pump, turn the pump on, and continue to evacuate the line set and indoor unit until the absolute pressure does not rise above 500 microns (29.9 inches of mercury) within a 20-minute period after shutting off the vacuum pump and closing the manifold gauge valves.
• F - When the absolute pressure requirement above has been met, disconnect the manifold hose from the vacuum pump and connect it to a cylinder of HFC-410A positioned to deliver liquid refrigerant. Open the manifold gauge valve 1 to 2 psig to release the vacuum in the line set and indoor unit.
• G - Perform the following:
  • Close manifold gauge valves.
  • Shut off HFC-410A cylinder.
  • Reinstall service valve cores by removing manifold hose from service valve. Quickly install cores with core tool while maintaining a positive system pressure.
  • Replace stem caps and finger tighten them, then tighten an additional one-sixth (1/6) of a turn as illustrated.

WARNING! Possible equipment damage. Avoid deep vacuum operation. Do not use compressors to evacuate a system. Extremely low vacuum can cause internal arcing and compressor failure. Damage caused by deep vacuum operation will void warranty.

STEP 4 – ELECTRICAL – Circuit Sizing and Wire Routing

In the U.S.A., wiring must conform with current local codes and the current National Electric Code (NEC). In Canada, wiring must conform with current local codes and the current Canadian Electrical Code (CEC).

Refer to the furnace or air handler installation instructions for additional wiring application diagrams and refer to the unit nameplate for minimum circuit ampacity and maximum overcurrent protection size.

24VAC TRANSFORMER: Use the transformer provided with the furnace or air handler for low-voltage control power (24VAC - 40 VA minimum).

⚠️ WARNING Electric Shock Hazard. Can cause injury or death. Unit must be properly grounded in accordance with national and local codes. Line voltage is present at all components when the unit is not in operation on units with single-pole contactors. Disconnect all remote electric power supplies before opening access panel. Unit may have multiple power supplies.

⚠️ WARNING Fire Hazard. Use of aluminum wire with this product may result in a fire, causing property damage, severe injury, or death. Use copper wire only with this product.

⚠️ WARNING Failure to use properly sized wiring and circuit breaker may result in property damage. Size wiring and circuit breaker(s) per Product Specifications bulletin (EHB) and unit rating plate.

ℹ️ IMPORTANT If unit is equipped with a crankcase heater, it should be energized 24 hours before unit start-up to prevent compressor damage as a result of slugging.

ELECTROSTATIC DISCHARGE (ESD) Precautions and Procedures

⚠️ WARNING Electrostatic discharge can affect electronic components. Take care during unit installation and service to protect the unit's electronic controls. Precautions will help to avoid control exposure to electrostatic discharge by putting the unit, the control, and the technician at the same electrostatic potential. Touch hand and all tools on an unpainted unit surface before performing any service procedure to neutralize electrostatic charge.

SIZE CIRCUIT AND INSTALL SERVICE DISCONNECT SWITCH

Refer to the unit nameplate for minimum circuit ampacity and maximum fuse or circuit breaker (HACR per NEC). Install power wiring and properly sized disconnect switch.

Diagram showing a main fuse box/breaker panel connected to a service disconnect switch.

INSTALL THERMOSTAT

Install room thermostat (ordered separately) on an inside wall approximately in the center of the conditioned area and 5 feet (1.5m) from the floor. It should not be installed on an outside wall or where it can be affected by sunlight or drafts.

Diagram showing thermostat placement on an interior wall, 5 feet from the floor.

NOTE: Units are approved for use only with copper conductors. Ground unit at disconnect switch or connect to an earth ground.

NOTE: 24VAC, Class II circuit connections are made in the control panel.

STEP 4 – ELECTRICAL (CONTINUED) – High Voltage and Field Control Wiring

The following illustration provides an example of control wiring connections when using a standard thermostat.

ROUTING HIGH VOLTAGE, GROUND AND CONTROL WIRING

HIGH VOLTAGE / GROUND WIRES: Any excess high voltage field wiring should be trimmed and secured away from any low voltage field wiring. To facilitate a conduit, a cutout is located in the bottom of the control panel. Connect conduit to the control panel using a proper conduit fitting.

FIELD CONTROL WIRING

Diagram showing field control wiring between a thermostat, indoor unit, and outdoor unit, with labels for R, W1, Y, G, C terminals.

NOTE: Wire tie provides low voltage control wire strain relief and maintains separation of field-installed low and high voltage circuits.

NOTE: For proper voltages, select thermostat wire (control wires) gauge per table above.

NOTE: Do not bundle any excess 24VAC control wires inside the control panel.

Install low voltage wiring from outdoor to indoor unit and from thermostat to indoor unit as illustrated.

• A - Run 24VAC control wires through hole with grommet and secure with provided wire tie.
• B - Make 24VAC thermostat wire connections. Locate the two wires from the contactor and make connection using field-provided wire nuts:
  • Yellow to Y1
  • Black to C (common)

Table: Wire Run Length and Gauge Requirements

24VAC Control Wiring Diagrams (Field Installed)

Figure 14: Displays various 24VAC control wiring diagrams for different thermostat and furnace/blower coil configurations, including ML17, EL280E, EL296E, ML296V, EL296V, SL280NV, and blower coil models (CBA25UH, CBA25UHV, CBA27UHE, CBA38MV).

NOTE: Refer to furnace, blower coil, and accessory instructions for additional wiring configurations with other optional controls.

Notes for Figure 14:

• Air handler shipped with jumpers installed between W1 and W2 and W2 and W3.
• R connection required for air conditioner with LSOM. Resistor kit (CAT #47W97) required when connecting ComfortSense 7000 with LSOM 2.
• L connection wired on units with LSOM.

STEP 5 – UNIT START-UP

ℹ️ IMPORTANT If unit is equipped with a crankcase heater, it should be energized 24 hours before unit start-up to prevent compressor damage as a result of slugging.

1. Rotate fan to check for binding.
2. Inspect all factory- and field-installed wiring for loose connections.
3. After evacuation is complete, open the liquid line and vapor line service valve stems to release the refrigerant charge (contained in outdoor unit) into the system.
4. Replace the stem caps and tighten to the value listed in Table 3.
5. Check voltage supply at the disconnect switch. The voltage must be within the range listed on the unit's nameplate. If not, do not start the equipment until you have consulted with the power company and the voltage condition has been corrected.
6. Connect manifold gauge set for testing and charging.
7. Set the thermostat for a cooling demand. Turn on power to the indoor unit and close the outdoor unit disconnect switch to start the unit.
8. Recheck voltage while the unit is running. Power must be within range shown on the unit nameplate.
9. Check system for sufficient refrigerant using the procedures outlined under Checking Refrigerant Charge.

OPERATING MANIFOLD GAUGE SET AND SERVICE VALVES

The liquid and vapor line service valves are used for removing refrigerant, flushing, leak testing, evacuating, checking charge, and charging. Each valve is equipped with a service port which has a factory-installed valve stem. Figures 15 and 16 provide information on how to access and operate both angle- and ball-type service valves.

Torque Requirements

When servicing or repairing heating, ventilating, and air conditioning components, ensure the fasteners are appropriately tightened. Table 3 lists torque values for fasteners.

Table 3 – Torque Requirements

ℹ️ IMPORTANT To prevent stripping of the various caps used, the appropriately sized wrench should be used and fitted snugly over the cap before tightening.

Using Manifold Gauge Set

When checking the system charge, only use a manifold gauge set that features low loss anti-blow back fittings. Manifold gauge sets used with HFC-410A refrigerant systems must be capable of handling the higher system operating pressures. The gauges should be rated for use with pressures of 0 - 800 psig on the high side and a low side of 30" vacuum to 250 psig (with dampened speed to 500 psi). Gauge hoses must be rated for use at up to 800 psig of pressure with a 4000 psig burst rating.

OPERATING BALL-TYPE SERVICE VALVE

1. Remove stem cap with an appropriately sized wrench.
2. Use an appropriately sized wrench to open. To open valve, rotate stem counterclockwise 90°. To close, rotate stem clockwise 90°.

Figure 15: Illustration of an operating ball-type service valve, showing how to open (rotate counterclockwise 90°) and close (rotate clockwise 90°). It depicts the valve stem, service port cap, service port core, and ball (shown closed).

OPERATING ANGLE-TYPE SERVICE VALVE

1. Remove stem cap with an appropriately sized wrench.
2. Use a service wrench with a hex-head extension (3/16" for liquid line valve sizes and 5/16" for vapor line valve sizes) to back the stem out counterclockwise as far as it will go.

Figure 16: Illustration of an operating angle-type service valve, showing how to open (back stem out) and close (front-seat stem). It depicts the valve stem, service port cap, service port core, and indicates when the service port is open to the line set and indoor unit.

NOTE: A label with specific torque requirements may be affixed to the stem cap. If the label is present, use the specified torque.

ACCESS SERVICE PORT / REINSTALL STEM CAP

A service port cap protects the service port core from contamination and serves as the primary leak seal.

1. Remove service port cap with an appropriately sized wrench.
2. Connect gauge set to service port.
3. When testing is completed, replace service port cap and tighten as follows:
   • With torque wrench, finger tighten and torque cap per Table 3.
   • Without torque wrench, finger tighten and use an appropriately sized wrench to turn an additional 1/6 turn clockwise.

Reinstall Stem Cap

Stem cap protects the valve stem from damage and serves as the primary seal. Replace the stem cap and tighten as follows:

• With torque wrench, finger tighten and then torque cap per Table 3.
• Without torque wrench, finger tighten and use an appropriately sized wrench to turn an additional 1/12 turn clockwise.

Figure 17: Diagrams showing the procedure for accessing service ports and reinstalling stem caps, including torque and turn specifications (1/6 turn and 1/12 turn).

Checking and Adding System Charge

The ML17XC1 unit is factory-charged with enough HFC-410A refrigerant to accommodate a 15-foot length of refrigerant piping. For refrigerant piping greater than 15 feet, calculate the additional charge using the table below. Then add the additional charge specified for the specific indoor coil match-up listed on the unit charging sticker.

Charge should be checked and adjusted using the tables provided on the charging procedure sticker on the unit access panel. Detailed information is given in the ML17XC1 Installation and Service Procedures manual, which is available on LennoxPros.com.

Refrigerant Charge per Line Set Length

*If line length is greater than 15 ft. (4.6 m), add this amount. If line length is less than 15 ft. (4.6 m), subtract this amount.

NOTE: Insulate liquid line when it is routed through areas where the surrounding ambient temperature could become higher than the temperature of the liquid line or when pressure drop is equal to or greater than 20 psig.

High Pressure Switch (S4)

This unit is equipped with a high-pressure switch located on the liquid line. The SPST, normally closed pressure switch opens when liquid line pressure rises above the factory setting of 590 ± 15 psig and automatically resets at 418 ± 15 psig.

Low Pressure Switch

This unit is equipped with a low-pressure switch located on the compressor suction line. The SPST, normally closed pressure switch opens when suction line pressure drops below the factory setting of 40 ± 5 psig and automatically resets at 95 ± 5 psig.

Homeowners Information

⚠️ CAUTION Before attempting to perform any service or maintenance, turn the electrical power to the unit OFF at the disconnect switch.

In order to ensure peak performance, your system must be properly maintained. Clogged filters and blocked airflow prevent your unit from operating at its most efficient level. The system should be inspected and serviced before each cooling and heating season by a licensed professional HVAC service technician (or equivalent).

Homeowner Maintenance

The following maintenance may be performed by the homeowner:

• Contact a licensed professional HVAC technician to schedule inspection and maintenance appointments for your equipment before each heating and cooling season.
• Check the indoor unit filter each month and replace the filter, if necessary.
• Have your Lennox dealer show you where your indoor unit filter is located. It will be either at the indoor unit (installed internal or external to the cabinet) or behind a return air grille in the wall or ceiling. Check the filter monthly and clean or replace it as needed. Disposable filters should be replaced with a filter of the same type and size.
• Check the indoor unit drain line for obstructions monthly. The indoor coil is equipped with a drain pan to collect condensate formed as your system removes humidity from the inside air. Have your dealer show you the location of the drain line and how to check for obstructions. (This would also apply to an auxiliary drain, if installed.)
• Check the area around the outdoor unit monthly and remove any obstructions that may restrict airflow to the outdoor unit. This would include grass clippings, leaves, or papers that may have settled around the unit.
• Trim shrubbery away from the unit and periodically check for debris which collects around the unit.
• During the winter months, keep the snow level below the louvered panels.

NOTE: The filter and all access panels must be in place any time the unit is in operation. If you are unsure about the filter required for your system, call your Lennox dealer for assistance.

IMPORTANT

ℹ️ IMPORTANT Sprinklers and soaker hoses should not be installed where they could cause prolonged exposure to the outdoor unit by treated water. Prolonged exposure of the unit to treated water (i.e., sprinkler systems, soakers, waste water, etc.) will corrode the surface of the steel and aluminum parts, diminish performance, and affect longevity of the unit.

Thermostat Operation

See the thermostat homeowner manual for instructions on how to operate your thermostat.

Pre-Service Check

If your system fails to operate, check the following before calling for service:

• Verify room thermostat settings are correct.
• Verify that all electrical disconnect switches are ON.
• Check for any blown fuses or tripped circuit breakers.
• Verify unit access panels are in place.
• Verify air filter is clean.

If service is needed, locate and write down the unit model number and have it handy before calling.

Professional Maintenance

NOTICE! Failure to follow instructions will cause damage to the unit.

This unit is equipped with an aluminum coil. Aluminum coils may be damaged by exposure to solutions with a pH below 5 or above 9. The aluminum coil should be cleaned using potable water at a moderate pressure (less than 50psi). If the coil cannot be cleaned using water alone, Lennox recommends use of a coil cleaner with a pH in the range of 5 to 9. The coil must be rinsed thoroughly after cleaning.

In coastal areas, the coil should be cleaned with potable water several times per year to avoid corrosive buildup (salt).

Your heating and air conditioning system should be inspected and maintained twice each year (before the start of the cooling and heating seasons) by a licensed professional HVAC technician. These checks may only be conducted by a licensed professional HVAC technician.

Outdoor Unit Checks:

1. Inspect component wiring for loose, worn, or damaged connections. Also check for any rubbing or pinching of wires. Confirm proper voltage plus amperage of the outdoor unit.
2. Check the cleanliness of the outdoor fan and blade condition (cracks) and clean or replace them, if necessary.
3. Inspect base pan drains for debris and clean as necessary.
4. Inspect the condition of refrigerant piping and confirm that pipes are not rubbing copper-to-copper. Also, check the condition of the insulation on the refrigerant lines. Repair, correct, or replace as necessary.
5. Test capacitor. Replace as necessary.
6. Inspect contactor contacts for pitting or burn marks. Replace as necessary.
7. Check outdoor fan motor for worn bearings/bushings. Replace as necessary.
8. Inspect and clean outdoor coils, if necessary, and note any damage to coils or signs of leakage.

Indoor Unit (Air Handler or Furnace) Checks:

1. Inspect component wiring for loose, worn, or damaged connections. Confirm proper voltage plus amperage of the indoor unit.
2. Inspect and clean or replace air filters in the indoor unit.
3. Check the cleanliness of the indoor blower and clean the blower, if necessary.
4. Inspect the indoor coil drain pans and condensate drains for rust, debris, obstructions, leaks, or cracks. Pour water in pans to confirm proper drainage from the pan through to the outlet of the pipe. Clean or replace as necessary.
5. Inspect and clean the indoor coil, if necessary.
6. Inspect the condition of the refrigerant lines and confirm that pipes are not rubbing copper-to-copper. Also, ensure that refrigerant pipes are not being affected by indoor air contamination. Check the condition of insulation on the refrigerant lines. Repair, correct, or replace as necessary.
7. Inspect the duct system for leaks or other problems. Repair or replace as necessary.
8. Check for bearing/bushing wear on the indoor blower motor. Replace as necessary.
9. Indoor unit service will also include inspection and cleaning of the burners, and a full inspection of the gas valve, heat exchanger, and flue (exhaust) system.

General System Test with System Operating:

1. Your technician should perform a general system test. They will turn on the air conditioner to check operating functions such as startup and shutoff operation. They will also check for unusual noises or odors, and measure indoor/outdoor temperatures and system pressures as needed. They will check the refrigerant charge per the charging sticker information on the outdoor unit.
2. Verify that system total static pressure and airflow settings are within specific operating parameters.
3. Verify correct temperature drop across the indoor coil.

ML17XC1 Start-Up and Performance Checklist

Fields for Customer, Indoor Unit Model, Outdoor Unit Model, Address, Serial, Notes.

START UP CHECKS

• Refrigerant Type:
• Rated Load Amps: ____ Actual Amps: ____ Rated Volts: ____ Actual Volts: ____
• Condenser Fan Full Load Amps: ____ Actual Amps: ____

COOLING MODE

• Suction Pressure: ___________ Liquid Pressure: ___________
• Supply Air Temperature: ___________ Ambient Temperature: ___________ Return Air Temperature: ___________

System Refrigerant Charge (Refer to manufacturer's information on unit or installation instructions for required subcooling and approach temperatures.)

Subcooling:

• Saturated Condensing Temperature (A)
• minus Liquid Line Temperature (B)
• A – B = SUBCOOLING

Approach:

• Liquid Line Temperature (A)
• minus Outdoor Air Temperature (B)
• A – B = APPROACH

Indoor Coil Temperature Drop (18 to 22°F):

• Return Air Temperature (A)
• minus Supply Air Temperature (B)
• A – B = COIL TEMP DROP