Lennox Merit Series CBA25UH Air Handler Installation Instructions

General Information

This manual provides installation instructions for the Lennox Merit Series CBA25UH Air Handler Units, designed for multi-position air handling. It is intended for servicing existing equipment only and is applicable to US applications. The unit is equipped with an all-aluminum coil and is designed for indoor installation. As shipped, the unit is ready for upflow, horizontal left-hand, or right-hand air discharge applications. Electric heat, downflow conversion kits, air filters, and other accessories are available.

Important Note: This manual is a general guide and does not supersede local or national codes. Always consult authorities having jurisdiction before installation.

The unit features a delay relay that delays the supply blower "ON" for 1 second and keeps it ON for 45 seconds on all fan and cooling demands.

Shipping and Packing List

Package 1 of 1 contains the assembled air handler unit, factory-equipped for upflow or horizontal air discharge applications, including upflow and horizontal drain pans and a preinstalled air filter. Check for shipping damage and contact the carrier if found. Verify the unit rating plate matches the order.

Important: Special procedures are required for cleaning the all-aluminum coil. Refer to page 19 for details.

Installation

The air handler must be installed as part of a matched system as outlined in the CBA25UH Product Specification bulletin. Installation must comply with all local, state, and national codes, including NFPA standards (NFPA No. 90A and NFPA No. 90B) and the National Electrical Code (ANSI/NFPA No. 70).

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 service agency.

WARNING: Every working procedure that affects safety shall only be carried out by competent persons. This appliance is not to be used by persons (including children) with reduced physical, sensory, or mental capabilities, or lack of experience and knowledge, unless they have been given supervision or instruction concerning its use by a person responsible for their safety. Children should be supervised to ensure they do not play with the appliance.

WARNING: Maximum Altitude of application is 3200m above sea level.

IMPORTANT: Excessive condensation may occur if the unit is installed in a warm, humid place. Sealant should be applied around electrical wires, refrigerant tubing, and condensate lines where they enter the cabinet. Seal electrical wires on the inside where they exit the conduit opening to prevent air leakage and condensate formation.

Installation Clearances

Specific clearances are required for non-ducted return closet installations. Louvers or return air grilles are field-supplied. Local codes may limit applications without a ducted return to single-story buildings. Minimum open areas for louvers vary by model size (-018/-024: 320 sq. in., -030/-036: 360 sq. in., -042: 450 sq. in.). If free area is unknown, assume 25% for wood or 75% for metal louvers.

For return air plenums, the return air grille should be immediately in front of the opening to allow free flow of return air. Adequate clearance must be maintained around the air handler for free flow of return air.

Upflow Application

The air handler must be supported on the bottom and set on a solid floor or field-supplied support frame. Securely attach the unit. For upflow applications, remove the horizontal drain pan for best efficiency and airflow. Connect return and supply air plenums using sheet metal screws. If no return air plenum is used, install the unit on a stand at least 14" from the floor for proper air return.

Horizontal Applications

IMPORTANT: Be careful when removing the coil assembly, as it may tip into the drain pan. Support the coil when removing it. A secondary drain pan is recommended for horizontal installations, especially in areas with high humidity. Ensure adequate support is provided for cabinet integrity and access to service panels.

Right-Hand Discharge: Determine required plugs for drain lines. Remove drain line plugs to install drain lines. Slope the unit toward the upflow drain pan end and ensure it is level from front to back. Rotate drain pan 180° and reinstall.

Left-Hand Discharge: Remove access panels and corrugated padding. Pull the coil assembly and horizontal drain pan from the unit. Remove drain plugs from back drain holes and reinstall on front holes. Rotate top cap 180° front-to-back. Align holes with unused screw holes on the coil end plates.

Condensate Drain

IMPORTANT: Traps must be installed in condensate drain lines (primary and auxiliary) to prevent the blower from drawing air through the drain lines into the air supply. The drain line should slope a minimum of 1 inch per 10 feet. A secondary drain pan is required in installations over finished living space or in areas that may be damaged by overflow from the main drain pan.

Test Condensate Drain: After installation, pour several quarts of water into the drain pan to ensure it drains completely and that fittings are not leaking.

Duct System and Filters

The air handler is provided with flanges for supply plenum connection. Duct systems should be adequately sized, insulated (minimum 1" thick with vapor barrier in conditioned areas, 2" in unconditioned areas), and sealed. Supply plenums should extend at least 3 ft. from the air handler before turning.

A filter is provided with each unit. Table 2 lists the filter sizes for each unit. High-efficiency filters require careful sizing to avoid reduced system capacity or performance.

Brazing Refrigerant Lines

Refrigerant lines must be connected by a qualified technician using specified line sizes for approved system combinations. Handle lines gently to avoid kinks. Keep the system closed to prevent moisture absorption by POE oils. Use silver alloy brazing rods with a melting point above 1,100°F (593°C). Do not use soft solder. Purge lines with nitrogen or dry air during brazing to prevent oxidation and moisture introduction. Ensure all connections are leak-tested, evacuated, and charged per ASHRAE Standard 15.2.

WARNING: Bleeding refrigerant charge from the high side may result in pressurization of the low side, potentially leading to ignition of refrigerant and oil mixture when a brazing torch is applied.

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

CAUTION: Brazing alloys and flux are hazardous. Avoid breathing vapors and perform operations in well-ventilated areas. Wear protective gear.

Electrical Connections

WARNING: Disconnect all power supplies before servicing. Ensure the unit is properly grounded. Wiring must conform to the National Electric Code (ANSI/NFPA No. 70) and local codes. Refer to wiring diagrams. Select supply circuit conductors according to NEC tables. The power supply must be sized and protected according to product specifications. This unit is factory-configured for 240 volt, single phase, 60 cycles. For 208-volt applications, refer to conversion instructions.

Separate openings are provided for 24V low voltage and line voltage. Use provided caps to seal unused holes.

Check-out Procedures

Pre-Start-Up Checks: Ensure the air handler is securely installed, sloped correctly (if horizontal), accessible for servicing, and that all necessary checks (duct system, drain lines, electrical connections, filters, etc.) are completed. Ensure an auxiliary drain pan is used where necessary.

Blower Operation: Set thermostat to FAN ON. The indoor blower should operate.

Cooling Operation: Set thermostat for cooling. The outdoor unit should start, and the indoor blower should operate within 30-60 seconds. Verify airflow from a register. Cycle off by setting the thermostat higher.

Electric Heat Operation (If Used): Set thermostat for auxiliary heat. Indoor blower and auxiliary heat should come on together. Allow time for sequencers to cycle. Cycle off by setting the thermostat so it does not call for heat.

Operation

Time Delay Relay: Provides a 1-second motor-on delay for cooling demand, ramps to 100% until demand is met, then runs for 45 seconds before ramping down.

Cooling: When the thermostat calls for cooling, the blower operates. The circuit to the outdoor unit contactor is closed, starting the compressor and outdoor fan motor.

Heating (Electric Heat Only): When the thermostat calls for heat, the heat sequencer energizes, followed by the heating elements and indoor blower motor.

Heating (Heat Pump): When the thermostat calls for heating, the blower operates. The circuit to the outdoor unit contactor is closed, starting the compressor and outdoor fan motor. Supplemental electric heat engages if room temperature drops.

Emergency Heat: If the thermostat is set to emergency heat, the heat pump is locked out, and all heating is electric. A jumper may be required for proper transfer.

Homeowner Maintenance

IMPORTANT: Do not operate the system without a filter. Filters protect the coil, blower, and internal parts. Inspect air filters monthly and replace or clean as needed. Dirty filters are a common cause of inadequate performance. Install new filters with arrows pointing in the direction of airflow. If secondary drain line discharges water, contact a qualified service technician.

Repairing or Replacing Cabinet Insulation

IMPORTANT: Damaged insulation must be repaired or replaced. Insulation loses its insulating value when wet, damaged, separated, or torn. Cut insulation in an X pattern, apply glue, and press back against the cabinet. If this is not possible, replace the insulation and tape any separations with foil-faced tape.

Professional Maintenance

NOTICE: Failure to follow instructions can cause damage to the unit. This unit is equipped with an aluminum coil, which may be damaged by solutions with a pH below 5 or above 9. Clean the coil with potable water (less than 50psi). If necessary, use a coil cleaner with a pH between 5 and 9, rinsing thoroughly. In coastal areas, clean the coil with potable water several times per year to avoid corrosive buildup.

Use of Air Handler During Construction

Lennox does not recommend using the air handler during construction due to low return air temperatures, harmful vapors, and clogged filters. If used, a room thermostat must control the unit, the air filter must be installed and maintained, and the unit, coil, fan assembly, and duct system must be thoroughly cleaned after construction. All operating conditions must be verified.

Decommissioning

Before decommissioning, ensure the technician is familiar with the equipment. Recover refrigerants safely. Isolate the system electrically. Ensure mechanical handling equipment, personal protective equipment, and recovery equipment are available and used correctly. Pump down the refrigerant system if possible. Remove refrigerant from various parts of the system. Ensure cylinders are properly situated and do not overfill. Recovered refrigerant shall not be charged into another system unless cleaned and checked.

Start-up and Performance Checklist

The checklist covers duct system, integrated control, voltage check, drain line, total external static, electric heat amps, indoor blower amps and CFM, temperature drop (cooling), and temperature rise (heating). It also includes thermostat settings and homeowner explanation.