Lennox CBX25UH Series

The CBX25UH Series is a line of high-efficiency air handlers designed for indoor installation, compatible with HFC-410A refrigerant. These units are engineered to be matched with 13 SEER air conditioners or heat pumps, though they can be paired with other air conditioning or heat pump systems as specified in the product bulletin. The series offers models ranging from 1-1/2 to 5 tons, catering to various residential and light commercial applications.

Function Description

The primary function of the CBX25UH air handler is to circulate conditioned air throughout a building, working in conjunction with an outdoor air conditioner or heat pump. It houses the indoor coil, blower motor, and control components necessary for air distribution and, when equipped, electric heating.

Air Distribution: The unit's blower motor draws return air from the conditioned space, passes it over the indoor coil (for cooling or heating from a heat pump), and then distributes the conditioned air through the supply ductwork. The blower motor is a single-phase direct drive type with a run capacitor and three speed taps (low, medium, high), allowing for flexible airflow adjustments.
Cooling Operation: When a cooling demand is initiated by the thermostat, the blower time-delay relay coil is energized, followed by the indoor blower relay. This activates the blower motor and completes the circuit to the outdoor unit's contactor, starting the compressor and outdoor fan motor. For heat pump applications, the reversing valve is also energized to the cooling position. A 1-second motor-on delay is incorporated, and the motor ramps up to 100% CFM. After the cooling demand is met, the motor runs at 100% CFM for 45 seconds before ramping down to stop.
Heating Operation (Heat Pump): In heat pump heating mode, the thermostat energizes the blower time-delay relay coil, activating the indoor blower motor and the outdoor unit's compressor and fan. The reversing valve remains de-energized, allowing the heat pump to provide heating.
Heating Operation (Electric Heat): If the unit is equipped with optional electric heat, a call for heat from the thermostat energizes a heat sequencer. After a time delay, the heating elements and the indoor blower motor activate. Units with multiple heat sequencers can be configured for multi-stage heating.
Emergency Heat (Heat Pump with Electric Heat): When the thermostat is set to emergency heat, the heat pump is locked out, and all heating is provided by the electric heat elements. A jumper on the thermostat subbase ensures the electric heat control transfers to the first-stage heat, allowing the indoor blower to cycle with the electric heat when the fan switch is in AUTO.
Refrigerant Management: All units come with a factory-installed check/expansion valve, which is internally installed for a cleaner setup and remains accessible for service. This valve is crucial for regulating refrigerant flow to the indoor coil.

Usage Features

The CBX25UH series offers several features designed for ease of installation, configuration, and reliable operation.

Flexible Installation: The unit is designed for indoor installation and, as shipped, is ready for either upflow or horizontal left-hand configurations. Field modifications are required for right-hand air discharge applications. Downflow air discharge application kits are also available as accessories.
Blower Speed Adjustment: The cooling blower speed is factory-configured to match the cooling capacity of the air handler's intended outdoor unit. However, if the outdoor unit has a smaller capacity, the blower speed can be easily adjusted by connecting different blower lead wires (RED for low, BLACK for high) to the blower relay harness. The factory-installed plastic cap should be reused on the unused connector.
Optional Electric Heat: The air handler supports field-installed electric heat sections, available in various kW ratings. These sections integrate into the control box, providing supplemental or primary heating capabilities.
Drain Pan Design: The units include factory-installed fiberglass-filled plastic drain pans. For horizontal applications, a secondary drain pan is recommended, especially when installed over finished living spaces, to prevent water damage from overflow. The drain lines require proper sloping and trapping to ensure complete drainage and prevent air from being drawn through the lines by the blower.
Duct System Integration: The air handler is equipped with flanges for connecting supply and return air plenums and ducts. These flanges can also form a filter rack for the air filter, or the filter can be installed within the return air duct system. Proper sizing and insulation of the ductwork are crucial for optimal performance.
Transformer: All units utilize a single line voltage to 24VAC transformer, rated at 40VA, located in the control box. 208/240VAC single-phase transformers have two primary voltage taps for compatibility.
Circuit Breaker Orientation: For horizontal right-hand discharge installations, the circuit breakers for optional electric heat must be rotated 180 degrees to ensure the "ON" position is correctly oriented upwards, as required by UL 1995.

Maintenance Features

The design of the CBX25UH incorporates considerations for simplified maintenance and service.

Access Panels: The air handler features easily removable access panels, secured by screws, to allow technicians to reach internal components such as the blower assembly, coil, and control box.
Coil Accessibility: The dual slab coils, arranged in an A-configuration, are designed to easily slide out of the unit cabinet, facilitating cleaning or replacement.
TXV Bulb Relocation: The TXV bulb, factory-installed internally, can be relocated to the exterior suction line. This relocation is highly recommended for improved performance and easier access for service.
Filter Access: The unit includes a dedicated filter access point, allowing for convenient inspection and replacement of the air filter.
Electrical Connections: The control box centralizes line voltage and electric heat connections. Wiring diagrams are provided on the unit access panel and in the manual to guide technicians through electrical troubleshooting and connections.
Condensate Drain Testing: After installation, the condensate drain system should be tested by pouring water into the drain pan to ensure complete drainage and check for leaks, which helps prevent future water damage.
Sealing the Unit: Maintaining an airtight seal around electrical wires, refrigerant tubing, and condensate lines where they enter the cabinet is important. This prevents warm, moist air from entering the cabinet, which could lead to condensation and blow-off problems, especially in unconditioned spaces. Duct tape or Permagum can be used for sealing.
Safety Precautions: The manual emphasizes the importance of disconnecting all power supplies before servicing, replacing all parts and panels before operating, and using copper conductors only. It also warns about electrostatic discharge affecting electronic components and the need to neutralize static charge before performing service. Physical contact with metal edges and corners should be avoided to prevent injury.

Lennox CBX25UH Series Specifications

General

Refrigerant	R-410A
Stages	Single Stage
Blower Motor Type	ECM
Cabinet Material	Galvanized Steel
Sound Level	Quiet operation
Operating Voltage	208/230V
Unit Dimensions	Varies by model
Unit Weight	Varies by model
Cabinet	Insulated
Coil	Aluminum
Warranty	5-Year Limited Warranty on covered components
Cooling Capacity	1.5 to 5 Tons
SEER Rating	Up to 16 SEER