Relays and Switches

VDOT Refrigerant Lines And Switches:

High Pressure Relief Valve

The compressor is equipped with a pressure relief valve which is placed in the system as a mechanical safety device. Under certain conditions, refrigerant pressure on the compressor discharge side may exceed the designed operating level. To prevent system damage, the valve is designed to open automatically at approximately 3654 + 483 kPa (530 + 69 psi) and vent refrigerant to the atmosphere. Any condition that causes this valve to open should be corrected, and the refrigerant oil and refrigerant should he replaced as necessary.

A/C Pressure Sensor

An electronic A/C pressure transducer is mounted on the discharge line (high side) of the A/C compressor hose assembly. Its output to the PCM is variable and is dependent upon pressure inside the line. A higher pressure results in a higher voltage output. A/C pressure is constantly monitored to:

^ Disengage the A/C clutch if the pressures are high-2700 kPa (430 psi).
^ Disengage the A/C clutch if pressures are too low-below 303 kPa (35 psi).
^ Control cooling fan operation of low and high speed.

A/C Compressor Control Relay

The A/C compressor control relay cycles the compressor on and off by energizing/de-energizing the compressor clutch coil.

With the key on, 12 volts is applied to the relay common contact and one coil terminal. The second coil terminal is grounded by the PCM when the driver selects A/C or defrost modes, and the pressure cycling switch is closed.

When the relay is energized current passes through the relay contacts which energizes the compressor clutch coil.