The heart of the AC system. Belt-driven pump that compresses low-pressure refrigerant vapor into high-pressure vapor.

Heat exchanger that dumps heat from refrigerant to ambient air. With the cooling package or on the tailgate and is often dirty.

Cold heat exchanger inside HVAC box. Absorbs heat from cab air. Includes freeze protection and drain system for condensate removal. Often plugged with debris and requires cleaning.

Stores liquid refrigerant, filters debris, and removes moisture with desiccant. Sometimes includes 535 psi pressure relief valve. Must be replaced when system is opened.

TXV (Thermal Expansion Valve) that meters refrigerant flow. Creates pressure drop that makes evaporator cold. Critical for proper system operation.

High-side pressure switch cuts out below 28 psi and above 384 psi. Prevents compressor operation under unsafe pressure conditions. Can be bypassed for testing with proper procedures.

AC switch, clutch, MCC (Electronic De-icing Thermostat), Auto HVAC Controller. Voltage-drop testing critical for AC switch diagnosis.

Fresh air and recirculating cab filters. Restricted airflow mimics low charge symptoms. Critical for proper evaporator performance and freeze prevention.

Heater control valve and temperature blending system. Hot coolant bypass can cause warm duct complaints even when AC is working properly. Watch for system to never cycle when you think it should. Duct temperature greater than ambient temperature.