Compressor HVAC: Description and Operation

A/C Compressor Relay On Conditions:

COMPRESSOR CONTROL
When the air conditioning switch is pushed in -- A/C switch: ON -- or the air outlet change-over control knob is moved to the DEF or DEF/FOOT position -- defroster switch: ON -- the air conditioning system operates and compressor control starts.

The fin thermo sensor, which senses the temperature of the air flowing out of the evaporator, is deactivated with temperature 3.2°C (38°F) or below.

Here the engine coolant temperature sensor senses the temperature of engine coolant, and it is turned off at 115°C (239°F) or higher temperatures.

The dual pressure switch turns OFF when the refrigerant pressure becomes excessively high or low, thus protecting the system.

When these two sensors are both activated, the dual pressure switch is ON and the ignition switch, blower switch, and air conditioning switch -- or defroster switch -- are ON, the A/C compressor relay is energized.