Lennox Merit® Series ML14KP1 Units Installation Instructions

General Information

This document provides installation instructions for the Lennox Merit® Series ML14KP1 Heat Pump units. It is designed for use with R-454B refrigerant and 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 local authorities having jurisdiction before installation.

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.

WARNING: To prevent serious injury or death: 1. Lock-out/tag-out before performing maintenance. 2. If system power is required (e.g., smoke detector maintenance), disable power to the blower, remove the fan belt where applicable, and ensure all controllers and thermostats are set to the “OFF” position before performing maintenance. 3. Always keep hands, hair, clothing, jewelry, tools, etc., away from moving parts.

IMPORTANT: Special procedures are required for cleaning the all-aluminum coil. Refer to page 20 for information.

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

CAUTION: Contact with sharp sheet metal edges can result in personal injury. Wear gloves and protective clothing.

NOTE: This unit ML14KP1 is a PARTIAL UNIT AIR CONDITIONER, complying with PARTIAL UNIT requirements of UL 60335-2-40/CSA C22.2 No. 60335-2-40, or UL 1995/CSA C22.2 No 236.

STEP 1 – Setting the Unit – Clearances

Proper clearances are crucial for unit performance and service access.

• 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 the unit.

Figure 1: Unit Dimensions. This diagram illustrates the unit's physical dimensions, labeled as 'A' and 'B', with measurements provided in inches and millimeters for various model numbers (ML14KP1-018-230 through ML14KP1-060-230).

Figure 2: Placement. This illustration shows recommended placement, including installing the unit away from windows and using two 90° elbows in the line set to reduce vibration.

Figure 3: Slab Mounting. This diagram shows how to install the unit level on a slab, maintaining a slope tolerance of 2 degrees (or 2 inches per 5 feet) away from the building structure.

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 damage to the roof surface.

IMPORTANT: This unit must be matched with an indoor coil as specified with AHRI. For AHRI Certified system match-ups and expanded ratings, visit www.LennoxPros.com.

Safety Warnings and Precautions

WARNING: Do not use means to accelerate defrosting or cleaning other than those recommended by the manufacturer. The appliance must be stored in a room without continuously operating ignition sources. Do not pierce or burn. Be aware that refrigerants may not contain an odor.

CAUTION: Servicing shall be performed only as recommended by the manufacturer.

WARNING: Ducts connected to an appliance shall not contain a potential ignition source.

WARNING: All working procedures affecting safety must be carried out by competent persons. This appliance is not for use by persons with reduced physical, sensory, or mental capabilities, or lack of experience and knowledge, unless supervised. Children should be supervised to ensure they do not play with the appliance.

IMPORTANT: Ensure adequate ventilation before breaking into the system or conducting hot work. Ventilation must continue during work.

IMPORTANT: Verify cabling will not be subject to wear, corrosion, excessive pressure, vibration, sharp edges, or other adverse environmental effects.

IMPORTANT: Pipe work, including material, routing, and installation, must include protection from physical damage and comply with national and local codes and standards (e.g., ASHRAE 15, IAPMO Uniform Mechanical Code, ICC International Mechanical Code, CSA B52). All field joints must be accessible for inspection.

CAUTION: Do not use potential sources of ignition for searching or detecting refrigerant leaks. Halide torches or other naked flame detectors are prohibited.

Acceptable leak detection methods include electronic leak detectors (calibrated for the specific refrigerant) and leak detection fluids. Avoid detergents containing chlorine. If a leak is suspected, remove/extinguish all naked flames. If brazing is required for a leak, recover all refrigerant first or isolate the affected part of the system.

CAUTION: Some leak detection soaps are corrosive to metals. Rinse piping thoroughly after testing. Do not use matches, candles, or flames to check for gas leaks.

WARNING: PARTIAL UNITS shall only be connected to an appliance suitable for the same refrigerant.

Refrigerant Handling and Safety

IMPORTANT: When breaking into the refrigerant circuit, use conventional procedures. For flammable refrigerants, follow best practices including safe removal, purging with inert gas, evacuation, and proper venting or cutting/brazing. Recover refrigerant into correct cylinders if venting is not allowed. For flammable refrigerants, purge the system with oxygen-free nitrogen to render it safe. This may require repeating the process. Do not use compressed air or oxygen for purging.

IMPORTANT: When charging the system, ensure no contamination of refrigerants occurs. Use short hoses to minimize refrigerant volume. Keep cylinders in appropriate positions. Earth the refrigerating system before charging. Label the system upon completion. Do not overfill the system. Pressure-test with purging gas and leak-test upon completion of charging, before commissioning. Perform a follow-up leak test before leaving the site.

IMPORTANT: When removing refrigerant for servicing or decommissioning, remove it safely. Use appropriate recovery cylinders, ensuring they are designated and labeled for the specific refrigerant. Cylinders must have pressure-relief valves and shut-off valves. Empty recovery cylinders should be evacuated and cooled if possible. Recovery equipment must be in good working order, with instructions, and suitable for all refrigerants, including flammable ones. Calibrated weighing scales and leak-free hoses are required. Check equipment for satisfactory working order and maintenance. Consult the manufacturer if in doubt.

Return recovered refrigerant to the supplier in the correct cylinder. Do not mix refrigerants. If compressors or oils are removed, evacuate them to an acceptable level to ensure no flammable refrigerant remains. Electric heating may be used to accelerate this process. Drain oil safely.

IMPORTANT: After field piping for split systems, pressure-test the pipework with an inert gas and vacuum-test before refrigerant charging. Field-made refrigerant joints indoors must be tightness tested with a sensitivity of 0.2 oz. per year of refrigerant or better.

Refrigerant Line Set Sizing and Installation

NOTE: R-454b is an A2L refrigerant. System installation must meet parameters based on total refrigerant charge, including line set. TAmin (Total Minimum Conditioned Area) is based on total system charge at sea level and must be multiplied by the altitude adjustment factor. Qmin refers to minimum airflow requirements for refrigerant leak mitigation.

TAmin Table provides minimum conditioned area based on refrigerant charge (lb/kg).

Altitude Adjustment Factor Table provides factors to adjust TAmin based on installed altitude (meters/feet).

Qmin Table lists required CFM based on refrigerant charge (lb/kg).

Figure 4: Refrigerant Line Set Isolation. This figure illustrates examples of proper refrigerant line set isolation for transition from vertical to horizontal, vertical runs, and horizontal runs. It emphasizes that refrigerant lines must not contact structure, and provides guidance on using hangers, straps, and sleeves.

Table 1: Refrigerant Line Set – Inches (MM). This table specifies the recommended liquid and vapor line sizes for various ML14KP1 models, including L15-41 and L15-65 line sets, and notes for field-fabricated connections.

Line Set Joints – Furnace Application. Evaporator primary line set joints require a line set joint sleeve. Additional joints must comply with specific options, potentially requiring a secondary refrigerant detection sensor.

Multiple Systems Installed in Same Space. For A2L refrigerant systems with additional joints, a refrigerant detection sensor must be installed below the burners. If all systems use direct vent, the sensor may not be needed.

Secondary Sensor Installation. Details on mounting secondary refrigerant sensors for upflow, downflow, and horizontal applications.

NOTE: For line sets longer than 50 feet, refer to the Refrigerant Piping Design and Fabrication Guidelines manual (Corp. 9351-L9) or contact Lennox Technical Support.

WARNING: When using high-pressure gas like nitrogen for pressurization, use a regulator that can control pressure down to 1 or 2 psig (6.9 to 13.8 kPa).

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

WARNING: Fire, Explosion, and Personal Safety hazard. Never use oxygen to pressurize or purge refrigeration lines, as it can cause fire or explosion.

WARNING: Polyolester (POE) oils used with R-454B absorb moisture quickly. Keep the system closed. Do not remove line set caps or service valve stub caps until ready to make connections.

IMPORTANT: Braze-free fittings must conform with UL207 or ISO14903.

STEP 2 – Refrigerant Piping

This section details procedures for refrigerant piping, including expansion valve installation and brazing.

1A/1B: Typical Existing Fixed Orifice/Expansion Valve Removal Procedure. Describes steps to remove existing components from the indoor coil, including disconnecting lines, removing fittings, and using temporary connections.

2: Connect Gauges and Equipment for Flushing Procedure. Outlines connecting gauges, a HCFC-22 cylinder, and a recovery machine for flushing the system.

3: Flushing Line Set. Details the process of flushing the line set and indoor unit coil using HCFC-22 and a recovery machine to remove existing refrigerant and prepare the system.

Figure 5: Flushing Procedure. Illustrates the equipment setup for flushing the line set.

STEP 2 – Refrigerant Piping – Brazing Procedures

1: Cut and Debur. Cut refrigerant lines square, debur ends, and ensure the pipe remains round. Do not crimp the end.

2: Cap and Core Removal. Remove service caps and cores from vapor and liquid line service ports.

3: Attach the Manifold Gauge Set for Brazing. Connect the gauge set for brazing, flowing regulated nitrogen (1-2 psig) through the liquid line service port and out the vapor line service port. Ensure the vapor service port is open for nitrogen escape.

CAUTION: Brazing alloys and flux are hazardous. Avoid breathing vapors, perform in well-ventilated areas, wear protective gear, and wash hands after handling.

WARNING: Danger of fire. Check pressures before applying heat. Applying a brazing torch to a pressurized system may result in ignition.

4: Wrap Service Valves. Wrap service valve bodies and copper tube stubs with water-saturated cloths to protect seals and paint during brazing.

5: Flow Nitrogen. Flow regulated nitrogen (1-2 psig) through the gauge set into the liquid service valve and out the vapor valve stem port.

6: Braze Line Set. Wrap service valves with water-saturated cloths before brazing. Ensure cloths remain saturated. Allow braze joints to cool, using additional cloths. Do not remove cloths until piping has cooled. Temperatures above 250°F can damage valve seals.

WARNING: Fire, Personal Injury, or Property Damage can occur if water-saturated cloths are not used. Quench the braze with water. Do not open service valves until leak-tested and evacuated.

7: Preparation for Next Step. After brazing, disconnect the manifold gauge set and apply water-saturated cloths to cool the piping. Remove cloths once cool.

Figure 6: Brazing Procedures. Illustrates cutting, deburring, cap/core removal, and manifold gauge set connection for brazing.

Figure 7: Brazing Line Set. Shows wrapping service valves and line sets with water-saturated cloths for brazing.

STEP 2 – Refrigerant Piping – Install Indoor Expansion Valve

This section details the installation of the expansion valve unit inside the cabinet, ensuring future service access.

Indoor Expansion Valve Installation. Describes steps for installing the check expansion valve, including placing Teflon® rings, attaching the valve to the liquid line orifice housing, and connecting the liquid line assembly. Torque specifications are provided.

Sensing Bulb Installation. Instructions for attaching the vapor line sensing bulb in the correct orientation on the vapor line, with specific positions for different line sizes and a note to never mount on the bottom of the line.

Equalizer Line Installation. Steps for removing existing fittings and connecting the equalizer line from the check expansion valve to the vapor port.

Figure 8: Expansion Valve Installation Details. Illustrates the indoor expansion valve installation, sensing bulb placement, and equalizer line connection.

STEP 3 – Leak Test and Evacuation

This section covers leak testing the system and evacuating it to remove air and moisture.

1: Connect Gauge Set. Connect the R-454B manifold gauge set to the outdoor unit's service ports (vapor and liquid lines). Connect the R-454B cylinder to the center port.

2: Test for Leaks. Pressurize the line set and indoor unit with a trace amount of R-454B, then check for leaks using a leak detector. Alternatively, pressurize with nitrogen to 160 psig and check for leaks to a sensitivity of 5 grams per year.

3: Evacuation – Connect Gauge Set. Connect the manifold gauge set, micron gauge, and vacuum pump to the service ports. Ensure cores are removed from service valves.

4: Evacuate the System. Start the vacuum pump and evacuate the system to 23,000 microns. Break the vacuum with nitrogen, then re-evacuate to 500 microns. After meeting requirements, introduce R-454B at 1-2 psig. Reinstall service valve cores and stem caps.

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.

Figure 9: Leak Test Setup. Shows the connection of the manifold gauge set, R-454B cylinder, and nitrogen cylinder for leak testing.

Figure 10: Evacuation Setup. Illustrates the connection of the manifold gauge set, micron gauge, vacuum pump, and R-454B/nitrogen cylinders for evacuation.

STEP 4 – Electrical – Circuit Sizing and Wire Routing

This section details electrical connections, circuit sizing, and wiring requirements.

Wiring Compliance: Wiring must conform to current local codes and the National Electric Code (NEC) in the U.S.A., and the Canadian Electrical Code (CEC) in Canada.

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

Refrigerant Detection System: Unit must be installed with the Lennox Approved Refrigerant Detection System (RDS) and sensor. Do not operate until the system is verified to be working.

WARNING: Electric Shock Hazard. Unit must be properly grounded. Line voltage is present at all components when the unit is not in operation. Disconnect all remote electric power supplies before opening access panels.

WARNING: Fire Hazard. Use only copper wire 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.

ELECTROSTATIC DISCHARGE (ESD) Precautions and Procedures: Take care during installation and service to protect electronic components. Touch an unpainted unit surface before performing service to neutralize static charge.

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

Install Thermostat: Install room thermostat 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.

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.

Figure 11: Electrical Installation Examples. Shows examples of service disconnect switch installation and thermostat placement.

STEP 4 – Electrical – (Continued) – High Voltage and Field Control Wiring

Single-Stage Heat Pump with Air Handler Control Wiring: This illustration provides an example of control wiring connections when using a standard thermostat, including connections for the thermostat, RDS sensor, and air handler.

Figure 12: Control Wiring Diagram. Depicts the wiring connections between the thermostat, RDS sensor, and the single-stage heat pump/air handler.

STEP 5 – Unit Start-Up

IMPORTANT: If the unit has a crankcase heater, it should be energized 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 vapor line service valve stems to release refrigerant charge into the system.
4. Replace stem caps and tighten per Table 2.
5. Check voltage supply at the disconnect switch. Ensure it is within the range listed on the unit's nameplate.
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.
9. Check system for sufficient refrigerant using procedures outlined under Checking Refrigerant Charge.

Operating Manifold Gauge Set and Service Valves: Liquid and vapor line service valves are used for refrigerant removal, flushing, leak testing, evacuation, checking charge, and charging. Figures 13 and 14 provide information on accessing and operating angle- and ball-type service valves.

Table 2: Torque Requirements. Lists recommended torque values for service valve caps, sheet-metal screws, machine screws, compressor bolts, and gauge port seal caps.

IMPORTANT: Use the appropriately sized wrench, fitted snugly, to prevent stripping caps.

Using Manifold Gauge Set: Use a manifold gauge set with low loss anti-blow back fittings, capable of handling R-454B system pressures (0-800 psig high side, low side vacuum to 250 psig). Gauge hoses must be rated for 800 psig working pressure.

Operating Ball-Type Service Valve: Instructions for removing and reinstalling stem caps and operating the valve (90° counterclockwise to open, 90° clockwise to close).

Figure 13: Ball-Type Service Valve Operation. Illustrates the operation of a ball-type service valve.

Figure 14: Operating Angle-Type Service Valve. Illustrates the operation of an angle-type service valve.

Access Service Port: Instructions for removing and replacing service port caps.

Reinstall Stem Cap: Instructions for replacing and tightening stem caps.

Figure 15: Reinstall Stem Cap / Service Port Cap. Shows the process of reinstalling stem and service port caps.

Charging

Verify the unit is electrically grounded before charging. Take extreme care not to overfill the system. Charge should be checked and adjusted using information on the charging label and tables.

R454B is a zeotropic blend with two saturation temperatures per pressure. Refer to the R454B Refrigerant Pressure Temperature Chart for values.

R454B Units must be charged with liquid refrigerant. Follow conventional procedures. The technician must mark the total charge (factory + additional) on the unit nameplate.

The ML14KP1 unit is factory-charged for a 15-foot refrigerant line. Add 3 oz of refrigerant for every 5 feet of piping beyond 15 feet.

Initiate cooling, allow pressures/temperatures to stabilize, and adjust charge using the subcooling method. Subcooling is calculated as Saturated Liquid Temperature minus Liquid Line Temperature.

Compare results with the unit charging label. Mark the total system charge on the nameplate.

Detailed information is in the ML14KP1 Installation and Service Procedures manual on LennoxPros.com.

Defrost System

This section covers:

• Emergency Heat
• Defrost System Overview
• Defrost Control Connections, Jumper Settings and Features
• Operational Mode Overview (Calibration, Normal and Defrost)
• Defrost Cycle Actuation

EMERGENCY HEAT (AMBER LIGHT): This feature is for when the outdoor unit is isolated or auxiliary electric heat is staged. An amber light indicates emergency heat mode. Use during outdoor unit shutdown or after a power outage if the outdoor temperature is below 50°F (10°C). Allow at least six hours for the crankcase heater to prevent compressor slugging.

Defrost System Details

The control monitors ambient temperature, outdoor coil temperature, and run time to determine defrost cycles. The coil temperature probe's placement is critical for proper operation.

Demand Defrost Control (A108) Diagnostic LEDs: Table 3 describes the status, fault, and lockout codes indicated by DS1 (Red) and DS2 (Green) LEDs.

Table 3: Demand Defrost Control (A108) Diagnostic LEDs. Details system status, fault codes, possible causes, and solutions for various LED states (e.g., Power problem, Normal operation, Ambient Sensor Problem, Low Pressure Fault, High Pressure Lockout).

Defrost Temperature Termination Jumper Settings (P1): Selections for termination temperature (50, 70, 90, 100°F). Default is 90°F if shunt is not installed.

Test Pins (P1) Function: Allows technicians to clear lockouts, cycle the unit in/out of defrost, or place the unit in defrost mode.

Nominal Defrost Time Selection Input: P3 header shunt positions determine nominal defrost time (140, 100, 60, 165 seconds).

Compressor Delay Mode (P5): A jumper on the DELAY pins cycles the compressor off for 30 seconds during defrost mode entry/exit to reduce sounds. This function is disabled when TEST pins are jumpered.

High Pressure Switch (S4): Located on the liquid line, opens when pressure rises above 590+15 psig and resets at 418+15 psig.

Low Pressure Switch (S87): Located on the suction line, remains open when suction pressure is low and closes when pressure rises above 40±5 psig.

Homeowner Information

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

Heat Pump Operation: Heat pumps deliver large amounts of warm air, which differs from furnaces. Frost on the outdoor coil in winter is normal; an electronic control activates a defrost cycle (5-15 minutes) to clear frost. Steam may be visible during defrost.

Homeowner Maintenance:

• Schedule professional HVAC inspection and maintenance annually.
• Check and replace the indoor unit filter monthly.
• Check the indoor unit drain line for obstructions monthly.
• Check the area around the outdoor unit monthly and remove obstructions.
• Trim shrubbery away from the unit and check for debris.
• During winter, keep snow level below louvered panels.

NOTE: The filter and all access panels must be in place when the unit is in operation.

IMPORTANT: Avoid prolonged exposure of the outdoor unit to treated water (e.g., sprinkler systems), as it can corrode parts, diminish performance, and affect longevity.

Thermostat Operation: Refer to the thermostat homeowner manual.

Pre-Service Check: Verify thermostat settings, electrical disconnects are ON, fuses/breakers are not tripped, access panels are in place, and the air filter is clean.

Extended Power Outage: Use the EMERGENCY HEAT setting during extended outages to protect the compressor. After a six-hour warm-up period, the thermostat can be switched to HEAT.

Professional Maintenance

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

Coil Cleaning: Aluminum coils may be damaged by solutions with pH below 5 or above 9. Clean with potable water (less than 50psi). If necessary, use a coil cleaner with a pH between 5 and 9. Rinse thoroughly. In coastal areas, clean with potable water several times per year to avoid salt buildup.

System Inspection: HVAC systems should be inspected and maintained twice a year by a licensed professional technician.

Outdoor Unit Checks: Inspect wiring, fan and blade condition, base pan drains, refrigerant piping, capacitor, contactor contacts, fan motor, and outdoor coils.

Indoor Unit (Air Handler or Furnace) Checks: Inspect wiring, air filters, and indoor blower.

Decommissioning: This procedure requires familiarity with the equipment. Recover refrigerants safely. Take oil and refrigerant samples if analysis is required. Ensure electrical power is available. Isolate system electrically. Ensure mechanical handling equipment, PPE, and proper recovery standards are met. Pump down system or remove refrigerant. Do not overfill cylinders. Label decommissioned equipment.