HVAC Compressor Controls Circuit Description

HVAC Compressor Controls Circuit Description

The engine drives the compressor for the HVAC system. The following components drive the compressor:

* A belt drive
* The A/C compressor clutch

The A/C compressor clutch permits the A/C compressor to disengage when the air conditioning is not used.

The A/C mode that is selected at the HVAC controller determines the operation of the compressor.

When the ignition switch is in the RUN position, system voltage is supplied through the A/C circuit breaker to the coil and the contacts of the A/C compressor relay.

The following conditions exist when the A/C is in the ON position:

* Terminal K of the HVAC controller is grounded.
* The A/C compressor relay is grounded.
* The contacts of the relay close.
* System voltage is supplied to the coil of the A/C compressor clutch.
* The coil is energized.
* The A/C compressor clutch engages.

The following sequence of events occurs when the A/C compressor is operating:

* The A/C system is charged with high pressure refrigerant.
* The refrigerant charge reaches the high setpoint.
* The A/C compressor refrigerant pressure switch opens.
* The A/C compressor clutch is de-energized.
* The refrigerant charge reaches the low setpoint.
* The A/C compressor refrigerant pressure switch closes.
* The A/C compressor clutch is re-energized.

The following actions occur if the A/C refrigerant pressure drops to a point that may cause icing of the evaporator:

* The A/C compressor cycling switch opens.
* The A/C compressor clutch is de-energized.

The following actions occur when the refrigerant pressure rises to a point that requires cooling:

* The A/C compressor cycling switch closes.
* The A/C compressor clutch is re-energized.

The A/C compressor clutch diode is connected across the terminals of the A/C compressor clutch.

The magnetic field around the clutch collapses whenever the clutch is de-energized. This action generates an induced voltage in the clutch coil. The diode provides a path for the current that results from the induced voltage. This action ensures that the other circuit components are not damaged.