Lennox XP19-024 - User Manual

The Lennox XP19 is a high-efficiency residential split-system heat pump unit designed for heating and cooling applications. It features a two-step scroll compressor and uses R410A refrigerant. The unit is intended for use with an expansion valve in the indoor unit and is available in 2, 3, 4, and 5-ton sizes.

Function Description

The XP19 operates on a two-stage modulated scroll compressor, which allows for smooth and continuous compression of gas. The compressor draws gas into crescent-shaped pockets formed by two scrolls, one stationary and one orbiting. As the orbiting scroll moves, the gas is forced toward the center, compressing it before discharge. This design provides efficient operation with fewer moving parts.

The unit incorporates a variable speed condenser fan motor, which adjusts its RPM to maintain constant airflow (CFM) and static pressure against the fan blade. This precise control of motor speed, achieved through pulse-width modulation, allows the motor to compensate for varying load conditions.

The XP19 utilizes a defrost control board that manages normal operation, calibration, and defrost cycles. In normal mode, the board monitors the O line, system operating mode (heat/cool), outdoor ambient temperature, coil temperature, and compressor run time to determine when a defrost cycle is needed. Calibration occurs after a defrost cycle to ensure no ice on the coil, establishing the temperature differential required for defrost. Defrost cycles are initiated based on frost detection (compressor runs longer than 34 minutes with a significant temperature difference between clear and frosted coil temperatures) or time (6 hours of heating mode compressor run time with coil temperature below 35°F).

A Lennox System Operation Monitor (LSOM) is integrated into the unit, providing diagnostic information through LED indicators. This 24-volt powered module helps troubleshoot system problems by indicating power status (GREEN), abnormal conditions (YELLOW flash codes), and thermostat demand without compressor operation (RED). The LSOM also manages the second-stage compressor solenoid output, energizing it when a Y2 call is received or when outdoor ambient temperature conditions warrant.

Usage Features

The XP19 is designed for residential use, providing both heating and cooling. Its two-step scroll compressor allows for efficient operation across different demand levels. The unit is charged with R410A refrigerant, and specific charging procedures are outlined for various line set lengths and outdoor ambient temperatures, using either the subcooling method or the approach method.

For charging, the system requires careful leak testing and evacuation to remove noncondensables and moisture, which can corrode internal components. The use of a thermocouple or thermistor electronic vacuum gauge calibrated in microns is recommended for accurate evacuation.

The unit's control system includes safety features such as a low pressure switch (S87) and a high pressure switch (S4) to protect the compressor from extreme operating conditions. These switches automatically reset and are ignored during initial startup, defrost, and specific temperature conditions to ensure proper operation.

Maintenance Features

Maintenance of the XP19 involves regular checks and procedures to ensure optimal performance and longevity. Key maintenance tasks include:

Coil Cleaning: The outdoor coil should be cleaned and inspected, potentially flushed with a water hose, after ensuring power is disconnected.
Fan Motor: The outdoor unit fan motor is prelubricated and sealed, requiring no further lubrication.
Leak Inspection: All connecting lines, joints, and coils should be visually inspected for oil leaks.
Wiring Checks: All wiring should be checked for loose connections.
Voltage and Amp-Draw: Verify correct voltage at the unit and check the amp-draw on the outdoor fan motor and compressor (both high and low capacity).
Drain Holes: Inspect and clean drain holes in the coil compartment base.
Refrigerant Charge: If insufficient cooling is reported, the refrigerant charge should be gauged and checked according to the provided charging instructions.
Component Replacement: If the system needs to be opened for service, such as compressor or filter drier replacement, strict precautions must be taken to prevent moisture from entering the system. This includes using nitrogen to break vacuum, quickly sealing components, and evacuating the system. Filter drier replacement is crucial to eliminate moisture from polyol ester oil.
Brazing Procedures: When making line set connections, dry nitrogen purging is required to prevent oxidation. Specific brazing rod types (silver alloy) are recommended, and wet rags should be used to protect nearby components from heat damage during brazing.

The defrost control board also includes diagnostic LEDs that indicate various operational conditions and fault codes, aiding in troubleshooting. These codes help identify issues such as power problems, sensor faults, low or high pressure faults, and circuit board failures. Resetting alert codes can be done manually by cycling 24VAC power to the LSOM or automatically when conditions return to normal.

The manual emphasizes that maintenance and service must be performed by a qualified installer or service agency to prevent property damage, personal injury, or loss of life. Electrical power must be disconnected before any service work to avoid shock hazards.

Lennox XP19-024 Specifications

General

Model	XP19-024
Type	Heat Pump
Cooling Capacity (BTU)	24000
Cooling Capacity (tons)	2
Heating Capacity (BTU)	24000
Heating Capacity (tons)	2
SEER Rating	19
HSPF Rating	10
Refrigerant	R-410A
Compressor Type	Variable Speed
Stages	Variable
Voltage	208/230
Phase	1
Unit Weight (Outdoor) lbs	220