Lennox Merit® Series 14HPX Units Installation Instructions

Important Safety Information

⚠️ 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.

ℹ️ The Clean Air Act of 1990 bans the intentional venting of refrigerant (CFCs, HCFCs and HFCs) as of July 1, 1992. Approved methods of recovery, recycling or reclaiming must be followed. Fines and/or incarceration may be levied for noncompliance.

ℹ️ This unit must be matched with an indoor coil as specified in the Lennox Engineering Handbook. Coils previously charged with HCFC-22 must be flushed.

⚠️ Electric Shock Hazard. Can cause injury or death. Unit must be grounded in accordance with national and local codes. Line voltage is present at all components when 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.

General Information

The Merit® 14HPX model is designed for use with HFC-410A refrigerant only. This unit must be installed with an approved indoor air handler or coil. Refer to the Lennox 14HPX Engineering Handbook for approved indoor component matchups.

ℹ️ This model is designed for use in expansion valve systems only. An indoor expansion valve approved for use with HFC-410A refrigerant must be ordered separately and installed prior to operating the system.

Unit Dimensions

The following table provides the dimensions for the 14HPX series units:

Diagram shows side views of the outdoor unit with dimensions labeled A, B, and C, indicating discharge air and suction/liquid line connections. An optional unit standoff kit is also noted.

Typical Unit Parts Arrangement

Diagram illustrates the internal components of the outdoor unit, including the Capacitor, Contactor, Defrost Control Board, Compressor Harness, Compressor, Reversing Valve, various pressure switches (Low and High), Filter Drier, and Service Valves (Liquid and Vapor Line). It also shows the control wiring loop and the cutout for high voltage conduit.

Model Number Identification

The unit model number is decoded as follows:

• 14HPX: Series designation.
• X: Indicates R-410A refrigerant.
• 024: Cooling Capacity in Tons (e.g., 024 = 2 Tons).
• 230: Voltage (208/230V-1phase-60hz).
• 2: Minor Revision Number.

Nominal SEER and Unit Type (HP = Heat Pump) are also indicated.

Warnings and Hazards

⚠️ Fiberglass Wool Hazard: This product may contain fiberglass wool. Disturbing insulation during installation, maintenance, or repair can expose you to fiberglass wool dust, which may cause lung cancer (as identified by the State of California) or respiratory, skin, and eye irritation. Consult material safety data sheets for more information.

⚠️ Physical Contact Hazard: Be aware of and use caution when working near metal edges and corners during installation or servicing to avoid personal injury.

ℹ️ Allen Wrench Requirements: Use Allen wrenches of sufficient hardness (50Rc minimum) and fully insert them into valve stem recesses to prevent stripping.

ℹ️ Service Valve Stem Torque: Service valve stems are factory-torqued to prevent refrigerant loss. Refer to Table 1 for torque values.

ℹ️ Cap Tightening: Use the appropriately sized wrench fitted snugly over caps before tightening to prevent stripping.

Torque Requirements: Table 1 lists recommended torque values for service valve caps, sheet metal screws, machine screws, compressor bolts, and gauge port seal caps.

Manifold Gauge Set Requirements: Use a manifold gauge set with low-loss, anti-blow back fittings suitable for HFC-410A refrigerant systems, capable of handling high operating pressures (0-800 psig high side, 30" vacuum to 250 psig low side), with gauge hoses rated for up to 800 psig.

Operating Service Valves

Liquid and vapor line service valves are used for refrigerant recovery, flushing, leak testing, evacuating, checking charge, and charging. Figure 1 illustrates how to access and operate angle-type and ball-type service valves.

Diagrams show angle-type and ball-type service valves, detailing their components (service port cap, core, stem) and operation (rotating stem counterclockwise to open, clockwise to close). It also shows how to access the service port by removing the cap and connecting a gauge set.

To Access Service Port: Remove the service port cap, connect the gauge set, and when finished, replace the cap and tighten it appropriately (finger tight plus 1/6 turn, or to specified torque).

Operating Angle Type Service Valve: Remove stem cap, use a service wrench with a hex-head extension to back the stem out counterclockwise.

Operating Ball Type Service Valve: Remove stem cap, use an appropriately sized wrench to open by rotating the stem 90° counterclockwise.

Reinstall Stem Cap: Replace the stem cap and tighten it finger tight plus an additional 1/12 turn clockwise, or to specified torque.

Recovering Refrigerant from Existing System

Follow these steps to recover refrigerant:

1. Disconnect Power: Disconnect all power to the outdoor unit at the service disconnect switch or main fuse box/breaker panel.
2. Connect Manifold Gauge Set: Connect a gauge set, clean recovery cylinder, and recovery machine to the unit's service ports.
3. Recovering Refrigerant: Remove existing refrigerant using one of the following methods.

ℹ️ Some systems may have higher refrigerant charges due to large internal coil volumes or long line sets.

Method 1: For units without shut-off valves or when flushing the system.

Method 2: For units with manual shut-off valves, using new refrigerant for flushing. Note potential issues like pressure switches tripping or compressor protection activating.

Procedure Note: If the compressor cannot pump down to a lower pressure, shut off the vapor valve, turn off main power, and use a recovery machine for remaining refrigerant.

Tasks: Start system in cooling mode, close liquid line valve, use compressor to pump HCFC-22 to outdoor unit until full, then turn off power and use recovery machine. Bypass low pressure switches if necessary. Close vapor line valve when low side pressure reaches 0 psig. Check gauges to ensure no backflow.

Diagram shows the setup for refrigerant recovery, including the outdoor unit, recovery machine, manifold gauges, and clean recovery cylinder connected to the service ports.

New Outdoor Unit Placement

Refer to Page 2 for unit dimensions and Figure 2 for mandatory installation clearance requirements.

Placement Considerations:

• Install unit away from windows to minimize sound transmission through glass.
• Consider local sound ordinances; position unit as far as possible from property lines.
• Maintain 30 inches (762 mm) clearance for service panel access.
• Maintain 36 inches (914 mm) clearance on three sides.
• One side may have 12 inches (305 mm) clearance, and the final side may have 6 inches (152 mm).
• Maintain 48 inches (1219 mm) clearance above the unit.
• Maintain 24 inches (610 mm) clearance between two units.

Figure 2 illustrates required installation clearances around the unit.

Placing Outdoor Unit on Slab: The top of the slab should be high enough to prevent water collection around the unit.

Figure 3 shows recommended placement away from windows, noting that two 90° elbows in the line set can reduce vibration.

Figure 4 depicts typical slab mounting at ground level, allowing for a slight slope away from the building.

Installing Outdoor Unit on Roof: Install at a minimum of 4 inches (102 mm) above the roof surface, ensuring weight is properly distributed over joists and rafters. Redwood or steel supports are recommended.

⚠️ Take proper precaution when lifting heavy objects.

New or Replacement Line Set

This section covers new installations or replacements. If not required, proceed to Brazing Connections on Page 9.

Ensure refrigerant lines routed through walls are sealed and isolated to prevent vibration transmission to the building structure.

Refrigerant Line Set: Field refrigerant piping consists of liquid and suction lines. Use Lennox L15 series line set or field-fabricated lines as listed in Table 2.

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

Longer Line Sets: For lines longer than 50 feet, contact Lennox Technical Support Product Applications or consult the Lennox piping manual. Provide unit model and size, line set diameters and total length, and number of elbows, rise, or drop.

Matching with Indoor Coil: If the indoor coil was previously charged with mineral oil or manufactured before Jan 1999, the coil and line set must be flushed. POE oils are used with HFC-410A; residual mineral oil can hinder heat transfer and clog the expansion device, voiding the warranty.

Line Set Isolation: Brazing alloys and flux are hazardous. Avoid breathing fumes, use ventilation, wear protective gear, and wash hands after handling.

Diagrams show methods for isolating refrigerant lines (vertical to horizontal transition, vertical runs, horizontal runs) using nylon ties, metal strapping, and sleeves to prevent contact with the structure.

⚠️ POE oils absorb moisture quickly. Keep the refrigerant system closed. Do not remove line set caps or service valve stub caps until ready to make connections.

Brazing Connections

Use silver alloy brazing rods (5-6% silver for copper-to-copper, 45% for copper-to-brass/steel).

1. Cut and Debur: Cut refrigerant lines square, debur ends, ensure pipe remains round, and do not pinch the line.
2. Cap and Core Removal: Remove service cap and core from vapor and liquid line service ports.
3. Attach Gauges: Connect gauge set low pressure side to liquid line service valve (A), and center port to nitrogen bottle with regulator (B). The service port must be open for nitrogen exit.
4. Wrap Service Valve: Protect components during brazing by wrapping the liquid line service valve body and copper tube stub with a wet cloth. Use another wet cloth underneath to protect the base paint.
5. Flow Nitrogen: Flow regulated nitrogen (1-2 psig) through the gauge set into the liquid line service valve port and out the vapor service valve port.
6. Braze Line Set: Braze the liquid line to the liquid line service valve. Turn off nitrogen flow. Point flame away from the service valve.
7. Install Service Port Caps: After brazing, disconnect the gauge set, cool piping with a wet rag, remove wrappings. Do not reinstall cores until after evacuation. Reinstall service port caps.

⚠️ Allow braze joint to cool before removing wet rag; temperatures above 250°F can damage valve seals.

ℹ️ Connect gauge set low pressure side to vapor line service valve and repeat procedure for brazing the liquid line to the service port valve.

Diagram illustrates the brazing process, including gauge connections, nitrogen flow, and flame placement.

Metering Devices and Flushing the System

This section covers flushing the line set and indoor coil (1 of 2).

Typical Fixed Orifice Removal Procedure: Details steps for removing the orifice housing and associated parts.

Typical Check Expansion Valve Removal and Replacement Procedure: Details steps for removing the expansion valve, sensing bulb, and associated lines.

Connect Gauges and Equipment for Flushing Procedure: Describes connecting the manifold gauge set, vacuum pump, and refrigerant cylinder.

Flushing Line Set: The line set and indoor unit coil must be flushed with the same amount of clean refrigerant previously used. Check the charge in the flushing cylinder. Set recovery machine for liquid recovery, open gauge valves to pull vacuum. Invert clean refrigerant cylinder to allow liquid refrigerant flow through the system. Recover vapor, then pull system down to 0. Close valves, pump out remaining refrigerant. The process involves using a recovery machine, clean refrigerant, and a vacuum pump.

Diagrams show the components for fixed orifice and expansion valve removal, as well as the setup for flushing the line set and indoor coil.

⚠️ This procedure should not be performed on systems with contaminants like a compressor burnout.

Leak Testing the System

Line Set and Indoor Coil Leak Test:

1. Connect Gauge Set: Connect HFC-410A manifold gauge set to the vapor valve service port (high pressure hose) and the liquid line service valve (low pressure hose). Connect HFC-410A cylinder to the center port.
2. Test for Leaks:
• Connect HFC-410A cylinder, open valve.
• Open high pressure side of manifold to introduce HFC-410A. Weigh in a trace amount (max 2 oz or 3 lbs pressure). Close cylinder and manifold valves. Disconnect HFC-410A cylinder.
• Connect dry nitrogen cylinder with regulator to the center port.
• Pressurize line set and indoor unit to 150 psig with nitrogen.
• After a few minutes, open a service valve port and check for leaks with a detector.
• Disconnect gauges from service ports.

Diagram shows the gauge set connected to the outdoor unit for leak testing, with nitrogen and HFC-410A cylinders.

⚠️ Use a regulator that controls pressure down to 1 or 2 psig when using high-pressure gas like dry nitrogen.

⚠️ Refrigerant can be harmful if inhaled. Use and recover responsibly.

⚠️ Never use oxygen to pressurize or purge refrigeration lines, as it can cause fire or explosion.

ℹ️ Leak detector must be capable of sensing HFC refrigerant.

Evacuating the System

Line Set and Indoor Coil Evacuation:

1. Connect Gauge Set: Remove cores from service valves. Connect manifold gauge set low side to vapor valve, high side to liquid line valve, micron gauge to the tee, and vacuum pump to the center port.
2. Evacuate the System: Open manifold valves and start vacuum pump. Evacuate to 23,000 microns (29.01 inches of mercury).

Diagram shows the setup for system evacuation, including the outdoor unit, manifold gauge set, micron gauge, vacuum pump, and nitrogen/HFC-410A connections.

Evacuation Notes: A rapid rise in pressure indicates a large leak. Absolute pressure is total pressure above absolute zero. After reaching 23,000 microns, close valves, turn off pump, disconnect hose. Connect hose to nitrogen cylinder, purge, and break vacuum. Shut off nitrogen, remove hose, open valves to release nitrogen. Reconnect vacuum pump and continue evacuation until pressure does not rise above 500 microns within 20 minutes after pump shutdown.

Final Steps: Connect manifold hose to HFC-410A cylinder, open valve to break vacuum. Close valves, shut off cylinder. Reinstall service valve cores and tighten stem caps.

⚠️ Avoid deep vacuum operation; do not use compressors for evacuation as it can cause internal arcing and compressor failure, voiding the warranty.

Non-condensables (gases that do not condense under operating temperatures/pressures) and water can corrode piping and compressor parts.

Electrical Connections

Wiring must conform to current local codes and the National Electric Code (NEC) or Canadian Electrical Code (CEC).

24VAC Transformer: Use the provided transformer for low-voltage control power (24VAC - 40 VA minimum).

Size Circuit and Install Service Disconnect Switch: Refer to the unit nameplate for minimum circuit ampacity and maximum fuse/breaker size. Install power wiring and a properly sized disconnect switch.

Install Thermostat: Install on an inside wall, approximately in the center of the conditioned area, 5 feet (1.5m) from the floor. Avoid outside walls or areas affected by sunlight or drafts.

Diagrams show typical electrical connections, including the service disconnect switch location and thermostat placement.

⚠️ Electric Shock Hazard. Unit must be grounded.

Note: Units are approved for use only with copper conductors. Ground unit at disconnect switch or earth ground.

Routing High Voltage/Ground and Control Wiring

Secure excess high voltage wiring away from low voltage wiring. Use the cutout in the control panel bottom for conduit.

Control Wiring: Install low voltage wiring from outdoor to indoor unit and thermostat. Run 24VAC control wires through a grommet and make connections to the control board (CMC1).

Wire Gauge: Use 18 AWG for runs less than 100 ft (30m) and 16 AWG for runs over 100 ft (30m), with a minimum 35°C temperature rating.

Diagrams illustrate typical control wiring for single-phase units, showing connections between the thermostat, indoor unit, and outdoor unit, including options for auxiliary heat. It also shows factory wiring and field wiring.

Figure 7 shows a typical field wiring diagram, detailing connections for the compressor, fan, reversing valve, and defrost control board.

Gauge Set Connections for Testing and Charging

Connect the manifold gauge set as follows:

• A: Connect center hose to HFC-410A cylinder for liquid phase charging.
• B: Connect low pressure side to the true suction port.
• C: Connect high pressure side to the liquid line service port.
• D: Position temperature sensor on the liquid line near the service port.

Diagram shows the gauge set connections for testing and charging, including the refrigerant tank, digital scale, and temperature sensor.

Servicing Units Delivered Void of Charge

If the outdoor unit is void of refrigerant:

1. Leak check the system (Page 11).
2. Evacuate the system (Page 12).
3. Use nitrogen to break the vacuum and install a new filter drier.
4. Evacuate the system again (Page 12).
5. Weigh in refrigerant (Figure 10).

Start-Up

ℹ️ Energize crankcase heater (if applicable) 24 hours before start-up to prevent compressor damage from slugging.

1. Rotate fan to check for binding.
2. Inspect all factory and field-installed wiring for loose connections.
3. After evacuation, open liquid and suction line service valves to release refrigerant charge.
4. Replace and tighten stem caps as specified.
5. Check voltage supply at disconnect switch; ensure it is within nameplate range. Consult power company if issues exist.
6. Set thermostat for cooling demand. Turn on indoor unit power and close outdoor unit disconnect switch.
7. Recheck voltage while unit is running.
8. Check system for sufficient refrigerant using Start-Up and Charging Procedures.
9. Recheck voltage while unit is running.

System Refrigerant

This section covers connecting gauge sets, checking indoor airflow, and adding/removing refrigerant.

Adding or Removing Refrigerant

This system uses HFC-410A refrigerant, which operates at higher pressures. Use only approved filter driers for HFC-410A. Do not use components designed for other refrigerants. This unit is NOT approved for coils using capillary tubes or fixed orifices.

Check airflow using the Delta-T (DT) process (Figure 9).

Airflow Adjustment (Delta-T Process):

• Measure entering air dry-bulb (A) and wet-bulb (B) temperatures to determine the desired Delta-T (DT) from the table.
• Measure entering (A) and leaving (C) air dry-bulb temperatures to find the actual temperature drop (TDrop = A - C).
• If the difference between TDrop and DT is within ±3°, no adjustment is needed.
• If TDrop is higher than DT, increase airflow. If TDrop is lower than DT, decrease airflow.
• Adjust fan speed according to indoor unit instructions.

Figure 9 shows the Delta-T chart and setup for measuring airflow and temperatures.

Weigh In Method

To calculate total refrigerant charge for a void system: Amount on nameplate + Adjustments for line set length + Additional charge for indoor unit matchup = Total charge.

Refrigerant Charge per Line Set Length: Table provides ounces per 5 feet based on liquid line diameter and set length adjustments.

Diagram illustrates the weigh-in method for calculating system charge.

Subcooling Method

Used for verifying refrigerant charge. Follow these steps:

1. Check indoor airflow (Figure 9).
2. Measure outdoor ambient temperature to determine cooling or heating mode.
3. Connect gauge set.
4. Check liquid and vapor line pressures against normal operating pressures (Table 10).
5. Set thermostat for cooling or heating demand.
6. Cooling Mode: Outdoor ambient ≥ 60°F (15°C). Target subcooling values are based on 70-80°F (21-27°C) indoor return air.
7. Heating Mode: Outdoor ambient < 60°F (15°C). Target subcooling values are based on 65-75°F (18-24°C) indoor return air.
8. Read liquid line temperature (LIQ°).
9. Read liquid line pressure, find corresponding temperature in Table 11 for SAT°, record it.
10. Calculate subcooling: SC° = SAT° - LIQ°.
11. Compare SC° results with tables (3-9), noting any additional charge for line set/matchup.
12. Add refrigerant if subcooling is low, remove if high.
13. Repeat steps 5-10 to verify charge.

Diagram shows the subcooling measurement setup.

Tables 3-9 provide target subcooling values and additional charge amounts for various indoor unit matchups.

Table 10 lists Normal Operating Pressures for cooling and heating.

Table 11 provides HFC-410A Temperature-Pressure (Psig) data.

System Operation

The outdoor unit and indoor blower cycle on demand from the thermostat. If the thermostat blower switch is ON, the indoor blower runs continuously.

Filter Drier: The unit has a large-capacity biflow filter drier. Replacement must be suitable for HFC-410A refrigerant.

Low Pressure Switch (Optional): Auto-reset switch that shuts off the compressor when vapor pressure falls below a set point (closes at/above 55 psig, opens at 25 psig). Ignored during defrost.

High Pressure Switch: Auto-reset switch that shuts off the compressor when discharge pressure rises above a set point (trips at 590 ± 10 psig).

Defrost System: The demand defrost controller detects ice build-up on the outdoor coil and initiates a defrost cycle. It self-calibrates and monitors ambient temperature, coil temperature, and run time.

Figure 12 shows the Defrost Control Board and its connections, including test pins, sensor plugs, pressure switch connections, and diagnostic LEDs.

Defrost Board Pressure Switch Connections: Automatic reset pressure switches (LO PS - S87, HI PS - S4) are wired to the defrost board.

5-Strike Lockout Feature: The control logic counts pressure switch trips. Five strikes result in a lockout, which can be reset by cycling 24V power or shorting TEST pins.

Diagnostic LEDs: Table 13 describes LED states (DS1 Red, DS2 Green) for diagnosing conditions like power problems, normal operation, sensor issues, and board failures.

Defrost System Sensors and Diagnostics

Sensors connect to the defrost board via a harness to detect outdoor ambient, coil, and discharge temperature faults. Resistance changes with temperature.

Table 12: Sensor Temp. / Resistance Range lists resistance values for Outdoor (Ambient), Coil, and Discharge sensors across various temperature ranges.

Figure 13 shows the locations of the ambient and coil sensors.

Note: Sensor resistance decreases as temperature increases. Faults are detected if sensors are open, shorted, or out of range.

Figure 14 provides a chart showing the temperature/resistance relationship for ambient and coil sensors.

Ambient Sensor: Detects outdoor temperatures below -35°F (-37°C) or above 120°F (48°C) as a fault. If faulty, the board reverts to time/temperature defrost.

Defrost Temperature Termination Shunt (Jumper) Pins: Selections for termination temperature (50, 70, 90, 100°F). Factory set at 50°F.

Delay Mode: A jumper on DELAY pins cycles the compressor off for 30 seconds entering/exiting defrost to reduce sounds.

Operational Description: The defrost control board operates in Normal, Calibration, or Defrost modes. It initiates defrost based on frost detection or time (every 6 hours of heating run time).

Test Mode: A test option is available for troubleshooting. Placing a jumper on TEST pins for 2-5 seconds can clear lockouts or cycle the unit into defrost.

Figure 15 illustrates the Test Mode flowchart for different conditions.

Table 13: Defrost Control Board Diagnostic LEDs details LED conditions, possible causes, and solutions for various faults and lockouts, including low/high pressure faults and discharge line/sensor faults.

Maintenance

⚠️ Dealer Maintenance Warning: Turn off electrical power before performing service or maintenance.

⚠️ General Maintenance Warning: Improper installation, adjustment, alteration, service, or maintenance can cause personal injury, loss of life, or property damage. Service must be performed by a qualified installer or service agency.

Outdoor Unit Maintenance

• Clean and inspect the outdoor coil (flush with water hose). Ensure power is off.
• Outdoor unit fan motor is pre-lubricated and sealed.
• Visually inspect lines, joints, and coils for oil leaks.
• Check all wiring for loose connections.
• Check voltage and amp draw at the unit.
• Inspect and clean drain holes in the coil compartment base.

Outdoor Coil Care: Flush the outdoor coil if exposed to corrosive substances or airflow obstructions (e.g., pet urine, seeds, fertilizers). Coastal locations require frequent inspections and washing due to salt corrosion.

Indoor Unit Maintenance

• Clean or change filters.
• Lennox blower motors are prelubricated and sealed.
• Adjust blower speed for cooling; check pressure drop for correct CFM.
• Check belt drive blowers for wear and tension.
• Check wiring, voltage, and amp draw for blower motor.
• Clean indoor coil and condensate line if necessary.

Homeowner Maintenance

Contact a trained service technician for coil cleaning. Schedule inspections and service, preferably twice a year.

⚠️ Homeowner Caution: Be aware of and use caution when working near metal edges and corners.

ℹ️ Homeowner Important Note: Avoid prolonged exposure of the outdoor unit to treated water (sprinklers, etc.) as it can corrode parts and diminish performance.

Routine Maintenance: Ensure peak performance by maintaining clean filters and clear airflow. Check filters monthly and clean/replace as needed. Use specified filter types. Clean reusable filters with mild soap and water.

Heat Pump Operation

Heat pumps deliver large volumes of warm air, differing from furnaces. Frost on the outdoor coil in winter (below 45°F / 7°C) is normal; an electronic control activates a defrost cycle (5-15 minutes) to clear frost. Steam may be visible during defrost; auxiliary heat may engage.

Extended Power Outage: The crankcase heater protects the compressor. During outages, use EMERGENCY HEAT setting. After a 6-hour compressor warm-up, switch to HEAT setting.

Preservice Check: Before calling for service, verify thermostat settings, ensure disconnect switches are ON, check fuses/breakers, confirm access panels are in place, and check the air filter.

Accessories: Refer to Lennox 14HPX Engineering Handbook, Product Catalog, and Price Book for more information.

14HPX Check List: A form is provided for recording installation and service details, including unit model, voltage, ampacity, fuse/breaker size, electrical connections, filter status, blower RPM, pressure readings, refrigerant charge, valve status, and thermostat calibration.