Lennox Merit Series ML14XC1 Units

General Information

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

This ML14XC1 outdoor air conditioner features an all-aluminum coil and is designed for use with HFC-410A refrigerant only. It must be installed with an approved indoor air handler or coil. Refer to the Lennox ML14XC1 Product Specifications bulletin (EHB) for approved indoor component matchups. These instructions provide a general guide and do not supersede local codes. Always consult authorities having jurisdiction before installation.

❗ IMPORTANT: Special procedures are required for cleaning the aluminum coil in this unit. Refer to page 15 for details.

Step 1: Setting the Unit - Clearances

Proper clearances are essential for unit operation and longevity. Refer to the diagram for placement guidance.

Clearance Notes:

• A 30-inch (762 mm) service clearance must be maintained on one side adjacent to the control box.
• A 36-inch (914 mm) clearance is required on one of the other three sides.
• One of the remaining two sides may have a 12-inch (305 mm) clearance, and the final side may have a 6-inch (152 mm) clearance.
• A 24-inch (610 mm) clearance must be maintained between two units.
• A 48-inch (1219 mm) clearance is required on top of the unit.

❗ NOTICE: Specific applications may require adjustments to the listed clearances to protect the unit from physical damage or to prevent conditions that limit operating efficiency. For example, clearances may need to be increased to prevent snow or ice from falling on the unit, or to prevent air recirculation when the unit is installed under a deck or in a tight space.

Diagram Description (FIGURE 1): A top-down view of the outdoor unit showing clearance zones labeled 'See NOTES' around the unit, with a designated 'CONTROL BOX' area.

Unit Dimensions

Diagram Description (FIGURE 2): A side view illustrating the unit's dimensions, labeled 'A' and 'B'.

TABLE 1: UNIT DIMENSIONS (Inches/MM)

Step 1: Unit Placement (Continued)

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

⚠️ CAUTION: Contact with sharp sheet metal edges can cause personal injury. Wear gloves and protective clothing when handling this equipment.

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

❗ IMPORTANT: Direct exhaust vents from dryers, water heaters, and furnaces away from the outdoor unit. Prolonged exposure to exhaust gases can cause condensation on the unit's metal components, reducing performance and longevity.

Placement Guidance: Install the unit away from windows.

Diagram Description (FIGURE 3): Illustrates two 90° elbows installed in the line set to reduce vibration.

Slab Mounting: Install the unit level. 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.

Diagram Description (FIGURE 4): Shows a unit mounted on a slab, with reference to building structure and ground level.

Step 2: Refrigerant Piping - Flushing Existing Line Set and Indoor Coil

Flush the existing line set according to the following instructions. For more detailed 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 coils if the system contains contaminants, such as from a compressor burn-out.

❗ IMPORTANT: If matching this unit with an approved line set or indoor unit coil previously charged with mineral oil, or manufactured before January 1999, the coil and line set must be flushed. Ensure all existing traps are emptied. Lennox units charged with HFC-410A refrigerant use Polyol ester (POE) oils. Residual mineral oil can act as an insulator, hindering heat transfer, and can clog the expansion device, reducing system performance. Failure to properly flush the system as instructed will void the warranty.

⚠️ 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, as it can cause fire or explosion when exposed to a spark or open flame.

⚠️ WARNING: When using high-pressure gas like nitrogen, use a regulator that controls 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 quickly. Keep the refrigerant system closed as much as possible. Do not remove line set or service valve stub caps until ready to make connections.

❗ IMPORTANT: Some scroll compressors have an internal vacuum protector that unloads scrolls when suction pressure drops below 20 psig. A hissing sound indicates unloading; the protector resets when pressure rises above 40 psig. DO NOT REPLACE THE COMPRESSOR.

Liquid Line Filter Drier Installation:

The provided filter drier must be 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). This ensures a clean, moisture-free system. Failure to install the filter drier will void the warranty. A replacement filter drier is available from Lennox. Refer to page 6 for brazing connection procedures.

Diagram Description (FIGURE 5): Illustrates the typical installation of a liquid line filter drier, showing flow direction from the outdoor unit's liquid line service valve to the filter drier and then to the indoor coil.

⚠️ WARNING: Refrigerant can be harmful if inhaled. Use and recover refrigerant responsibly. Failure to follow this warning may result in personal injury or death.

Note: For refrigerant lines longer than 50 feet, consult the Refrigerant Piping Design and Fabrication Guidelines manual (Corp. 9351-L9) or contact the Lennox Technical Support Department.

TABLE 2: REFRIGERANT LINE SET SIZES (Inches/MM)

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

Step 2: Refrigerant Piping - Brazing Procedures

1. Cut and Debur: Cut refrigerant line ends square (free from nicks or dents) and debur them. Ensure the pipe remains round; do not crimp the end.

2. Cap and Core Removal: Remove the service cap and core from both the suction and liquid line service ports.

Diagram Description: Illustrates correct line set size matching service valve connections and shows components like service port caps, cores, and different valve types (angle-type, ball-type). It also warns against crimping the service valve connector when the pipe is smaller than the connection.

3. Attach Manifold Gauge Set: Connect the manifold gauge set for brazing liquid and suction line service valves. Flow regulated nitrogen (1 to 2 psig) through the low-side gauge set into the liquid line service port valve and out the suction line service port valve.

Diagram Description (FIGURE 8): Shows the manifold gauge set connected to the outdoor unit's service valves. Nitrogen is flowing through the system. It indicates to point the flame away from the service valve when brazing.

⚠️ CAUTION: Brazing alloys and flux are hazardous. Avoid breathing vapors or fumes. Perform operations in well-ventilated areas. Wear gloves and protective goggles or face shield.

⚠️ WARNING: Danger of fire. Bleeding refrigerant charge from the high side can pressurize the low side. Applying a brazing torch to a pressurized system may ignite the refrigerant and oil mixture. Check pressures before applying heat.

4. Wrap Service Valves: Use water-saturated cloths around service valve bodies and copper tube stubs to protect valve seals during brazing. Use additional cloths underneath the valve body to protect paint.

5. Flow Nitrogen: Continue flowing nitrogen (1 to 2 psig) through the gauge set into the liquid service valve and out the suction valve stem port.

6. Braze Line Set: Wrap both service valves with water-saturated cloths before brazing. Keep cloths saturated throughout the brazing and cool-down process.

❗ IMPORTANT: Allow the braze joint to cool. Use additional water-saturated cloths to cool the joint. Do not remove cloths until piping has cooled. Temperatures above 250°F can damage valve seals.

⚠️ WARNING: Fire, personal injury, or property damage may result if water-saturated cloths are not used properly. The braze must be quenched with water to absorb residual heat. Do not open service valves until refrigerant lines and indoor coil have been leak-tested and evacuated.

7. Preparation for Next Step: After brazing, disconnect the manifold gauge set. Apply additional water-saturated cloths to cool the piping. Once cool, remove all cloths.

Step 2: Refrigerant Piping - Installing Indoor Expansion Valve

This outdoor unit is designed for systems using either a fixed orifice (RFC) or an expansion valve metering device. Refer to the ML14XC1 Product Specifications bulletin (EHB) for approved expansion valve kit matchups. The expansion valve can be installed internally or externally to the indoor coil.

Indoor Expansion Valve Installation:

Diagram Description: Shows the installation of an expansion valve, including components like distributor tubes, liquid line orifice housing, check/expansion valve, sensing line, and equalizer line. Steps C-F detail the connection process, including tightening specifications (1/2 turn or 20 ft-lb).

Sensing Bulb Installation:

Diagram Description: Illustrates the correct orientation for attaching the suction line sensing bulb using a clamp and screws. It provides notes on preferred placement on horizontal runs and acceptable placement on vertical runs, emphasizing proper thermal contact. It also details placement on different pipe sizes (3 or 9 o'clock for smaller pipes, 4 or 8 o'clock for larger pipes), warning against bottom placement.

Equalizer Line Installation:

Diagram Description: Shows how to remove the flare seal cap or nut and connect the equalizer line from the check/expansion valve to the suction line's equalizer port.

Step 3: Leak Test and Evacuation

Leak Test:

1. Connect Gauge Set: Connect the high-pressure hose of an HFC-410A manifold gauge set to the suction valve service port. Connect the HFC-410A cylinder to the center port of the manifold gauge set.

Diagram Description (FIGURE 10): Shows the manifold gauge set connected to the outdoor unit, with HFC-410A and nitrogen cylinders. It illustrates the initial connection for leak testing.

2. Test for Leaks:

a. Connect the HFC-410A cylinder (vapor only) and open the high-pressure side of the manifold to allow HFC-410A into the line set and indoor unit. Introduce a trace amount of HFC-410A (max 2 oz / 57g). Close the cylinder and manifold valves, then disconnect the HFC-410A cylinder.

b. Connect a nitrogen cylinder with a regulator to the center port. Adjust nitrogen pressure to 150 psig (1034 kPa) and open the high-side manifold valve to pressurize the system.

c. After a few minutes, open a service valve port and check for leaks with a leak detector.

d. After leak testing, disconnect gauges.

Evacuation:

3. Connect Gauge Set: Connect the low-side manifold gauge set with a 1/4 SAE in-line tee to the suction line service valve. Connect the high-side to the liquid line service valve. Connect a micron gauge and the vacuum pump to the center port.

Diagram Description (FIGURE 11): Details the setup for evacuation, showing the manifold gauge set, micron gauge, vacuum pump, and connections to the unit's service valves. It also shows connections for HFC-410A and nitrogen.

4. Evacuate the System:

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

b. Note: A rapid pressure rise indicates a leak. Repeat leak testing if necessary.

c. Once 23,000 microns is reached, close manifold valves and vacuum pump valve, turn off the pump. Disconnect the vacuum pump hose. Connect the hose to a nitrogen cylinder (set to 150 psig) and purge the hose. Open manifold valves to break the vacuum.

d. Shut off nitrogen, disconnect hose, and open manifold valves to release nitrogen.

e. Reconnect the vacuum pump and continue evacuation until the absolute pressure does not rise above 500 microns within a 20-minute period after shutting off the pump and closing valves.

f. Once the 500-micron requirement is met, disconnect the vacuum pump hose and connect it to an HFC-410A cylinder to introduce 1 to 2 psig.

g. Close manifold valves, shut off HFC-410A cylinder. Reinstall service valve cores using a core tool while maintaining positive system pressure. Replace stem caps and tighten.

⚠️ WARNING: Avoid deep vacuum operation. Do not use compressors to evacuate systems. Extremely low vacuum can cause internal arcing and compressor failure, voiding the warranty.

Step 4: Electrical - Circuit Sizing and Wire Routing

Wiring must conform to current local codes and the National Electric Code (NEC) in the U.S.A., and Canadian Electrical Code (CEC) in Canada. Refer to furnace/air handler instructions and unit nameplate for circuit ampacity and overcurrent protection.

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. Unit must be properly grounded. 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 panels.

❗ IMPORTANT: If the unit has a crankcase heater, it should be energized 24 hours before start-up to prevent compressor damage from slugging.

⚠️ WARNING: Fire Hazard. Use only copper wire with this product. Aluminum wire may cause fire, property damage, severe injury, or death.

⚠️ CAUTION: Failure to use properly sized wiring and circuit breakers may result in property damage. Size wiring and breakers per the Product Specifications bulletin (EHB) and unit rating plate.

⚠️ CAUTION: Electrostatic discharge (ESD) can affect electronic components. Take care during installation and service to protect the unit's electronic controls by neutralizing 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 a properly sized disconnect switch.

Diagram Description: Shows a main fuse box/breaker panel and a service disconnect switch.

Install Thermostat: Install the room thermostat (ordered separately) on an inside wall, approximately in the center of the conditioned area, 5 feet (1.5m) from the floor. Avoid installing on an outside wall or where it can be affected by sunlight or drafts.

Diagram Description: Illustrates thermostat placement on an interior wall.

Note: Units are approved for use only with copper conductors. Ground the unit at the disconnect switch or connect to an earth ground. 24VAC, Class II circuit connections are made in the control panel.

Step 4: Electrical (Continued) - High Voltage and Field Control Wiring

The following illustrates an example of control wiring connections using a standard thermostat.

Routing High Voltage, Ground and Control Wiring:

Secure any excess high voltage field wiring away from low voltage wiring. Use a conduit cutout in the control panel bottom. Connect conduit using a proper fitting.

Diagram Description (FIGURE 13): Shows field control wiring between a thermostat, indoor unit, and outdoor unit, indicating connections for power, heat, cooling, and blower. It also provides notes on wire ties for strain relief and wire gauge selection.

24VAC Control Wiring Diagrams (Field Installed):

Diagram Description (FIGURE 14): Provides detailed 24VAC control wiring diagrams for various Lennox thermostats (ComfortSense 5500, 7500) and units (furnaces, air handlers, outdoor units), showing specific terminal connections.

Step 5: Unit Start-Up

❗ IMPORTANT: If the unit is equipped with a crankcase heater, it should be energized 24 hours before unit start-up to prevent compressor damage from slugging.

Start-Up Procedure:

1. Rotate the fan to check for binding.
2. Inspect all factory- and field-installed wiring for loose connections.
3. After evacuation, open the liquid line and suction line service valve stems to release the refrigerant charge into the system.
4. Replace stem caps and tighten to the value listed in Table 3.
5. Check voltage supply at the disconnect switch. Ensure it is within the range listed on the unit's nameplate. Consult the power company if voltage is incorrect.
6. Connect the manifold gauge set for testing and charging, following Figure 10 guidelines.
7. Set the thermostat for 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 to ensure it is within the nameplate range.
9. Check system for sufficient refrigerant using the procedures outlined under System Refrigerant.

Operating Manifold Gauge Set and Service Valves:

Service valves (liquid and suction) are used for refrigerant removal, flushing, leak testing, evacuation, charge checking, and charging. Each valve has a service port with a factory-installed valve stem. Figures 15 and 16 provide information on accessing and operating angle- and ball-type service valves.

Torque Requirements:

TABLE 3: TORQUE REQUIREMENTS

❗ IMPORTANT: Use the appropriately sized wrench, fitted snugly over the cap, before tightening to prevent stripping.

Using Manifold Gauge Set: Use a manifold gauge set with low-loss, anti-blowback fittings. For HFC-410A systems, the set must handle higher operating pressures (0-800 psig high side, 30" vacuum to 250 psig low side) and hoses rated for up to 800 psig.

Operating Ball-Type Service Valve:

Diagram Description (FIGURE 15): Shows a ball-type service valve in the closed position, with instructions to remove the stem cap and use a wrench to open/close the valve by rotating the stem 90° counterclockwise/clockwise.

Operating Angle-Type Service Valve:

Diagram Description (FIGURE 16): Shows angle-type service valves in both open (back-seated) and closed (front-seated) positions, with instructions on how to operate them using a service wrench with a hex-head extension.

To Access Service Port:

1. Remove the service port cap (primary leak seal) with an appropriately sized wrench.

2. Connect the gauge set to the service port.

3. After testing, replace the service port cap and tighten (finger tight, then an additional 1/6 turn clockwise if no torque wrench is used).

Reinstall Stem Cap: Replace the stem cap and tighten (finger tight, then an additional 1/12 turn clockwise if no torque wrench is used).

Diagram Description (FIGURE 17): Illustrates the process of tightening the service port cap and stem cap, showing the 1/6 and 1/12 turn increments.

Checking and Adding System Charge

The ML14XC1 unit is factory-charged for a 15-foot refrigerant piping length. Check and adjust charge using tables on the unit's charging procedure sticker. Detailed information is in the ML14XC1 Installation and Service Procedures manual (Corp1502-L7), available on LennoxPros.com.

Homeowner Information:

⚠️ CAUTION: Turn off electrical power at the disconnect switch before performing any service or maintenance.

For peak performance, ensure the system is properly maintained. Clogged filters and blocked airflow reduce efficiency. The system should be inspected and serviced annually by a licensed professional HVAC technician.

Homeowner Maintenance:

• Schedule yearly inspections and maintenance with a licensed HVAC technician.
• Check the indoor unit filter monthly and replace if necessary.
• Check the indoor unit drain line for obstructions monthly during the cooling season.
• Check the area around the outdoor unit monthly and remove any obstructions that may restrict airflow (e.g., grass clippings, leaves).
• Trim shrubbery away from the unit and check for debris.
• During winter, keep snow levels below the louvered panels.

Note: Ensure the filter and all access panels are in place during operation.

Professional Maintenance Checks

❗ IMPORTANT: Sprinklers and soaker hoses should not cause prolonged exposure to the outdoor unit from treated water, as this can corrode metal parts and diminish performance.

Thermostat Operation: Refer to the thermostat owner's manual.

Pre-Service Check: Before calling for service, check:

• Room thermostat settings.
• Electrical disconnect switches are ON.
• Blown fuses or tripped circuit breakers.
• Unit access panels are in place.
• Air filter cleanliness.
• If service is needed, note the unit model number.

Professional Maintenance (Technician Tasks):

Outdoor Unit:

1. Inspect wiring for loose/damaged connections and rubbing/pinching.
2. Check fan and blade cleanliness and condition.
3. Inspect and clean base pan drains.
4. Inspect refrigerant piping for rubbing or damage and check insulation condition.
5. Test capacitor and replace if necessary.
6. Inspect contactor contacts for pitting/burn marks.
7. Check outdoor fan motor bearings/bushings.
8. Inspect and clean outdoor coils.

Indoor Unit (Air Handler or Furnace):

1. Inspect wiring for loose/damaged connections.
2. Inspect and clean/replace air filters.
3. Check and clean indoor blower.
4. Inspect evaporator coil drain pans and condensate drains for obstructions/leaks.
5. Inspect and clean evaporator coil.
6. Inspect refrigerant lines for rubbing or contamination effects and check insulation.
7. Inspect duct system for leaks.
8. Check indoor blower motor bearings/bushings.
9. For gas/oil furnaces: inspect burners, gas valve, heat exchanger, and flue system.

❗ NOTICE: Failure to follow instructions will cause unit damage. Aluminum coils can be damaged by solutions with pH below 5 or above 9. Clean with potable water at moderate pressure (under 50 psi). If necessary, use a coil cleaner with pH between 5 and 9. Rinse thoroughly. In coastal areas, clean with potable water several times per year to avoid salt buildup.

General System Test with System Operating

Your technician should perform a general system test, checking:

• Startup and shutoff operation.
• Unusual noises or odors.
• Indoor/outdoor temperatures and system pressures.
• Refrigerant charge (per charging sticker).
• System total static pressure and airflow settings.
• Correct temperature drop across the indoor coil.

ML14XC1 Start-Up and Performance Checklist:

This checklist is used to record operational data during start-up, including:

• Customer Indoor Unit Model, Address, Serial Number
• Outdoor Unit Model, Serial Number
• Refrigerant Type
• Rated Load Amps, Actual Amps (Condenser Fan, Cooling Mode)
• Rated Volts, Actual Volts
• Suction Pressure, Liquid Pressure
• Supply Air Temperature, Return Air Temperature
• Ambient Temperature
• System Refrigerant Charge (Subcooling and Approach temperatures)
• Indoor Coil Temperature Drop