Auxiliary Engine Coolant Fan A/C Pressure Switch (P42 Diesels and all P32)
The air conditioning (A/C) fan pressure switch is located on top of the receiver/dryer. The switch is normally open, but closes as a result of rising pressure. When the switch closes, the fan relay is energized. The switch requires 1620 kPa (235 psi) +/- 206.8 kPa (30 psi) in order to close.
A/C Compressor High Pressure Cutoff Switch
The high pressure cut-off switch is located on the rear cover of the compressor. This switch is normally closed, but opens at pressures of 2827-3103 kPa (410-450 psi) in order to interrupt the voltage to the air conditioning (A/C) clutch circuit. When the high pressure switch opens, the compressor stops cycling and the pressure relief valve is prevented from discharging refrigerant and oil.
A/C Compressor Refrigerant Pressure Switch
The evaporator (low) pressure switch is located on the suction line near the evaporator. The switch is normally open, but will close at 185 kPa (27 psi) +/- 35 kPa (5 psi). At pressures below 38 kPa (5.5 psi) +/- 24 kPa (3.5 psi), the switch opens and interrupts the air conditioning (A/C) clutch circuit.
A/C Compressor Relay
This relay is controlled by the VCM (Gas), PCM (Diesel, electronic fuel injection) or by the pressure switches (Diesel, mechanical fuel injection).This relay controls power to the A/C compressor clutch.
