Pressure Switch

Pressure monitor

In car air conditioning, the pressure switch monitors the A/C loop’s high pressure level and enables or disables the compressor according to two pressure thresholds. The pressure switch can be screwed to the pipe, dryer or condenser. 

One additional circuit controls the air conditioner’s cooling fan, securing the condensation process by forcing air flow through the condenser. In essence, the pressure switch is a safety device for the A/C loop. It is located on the high pressure side of the air conditioning loop.

 

Roles of the pressure switch

The pressure switch has three main roles:

• It monitors the loop’s high pressure and detects if it is too high (P2 > 27 to 32 bars)
• It monitors and detects when pressure is too low (P1 2 bars)
• It includes one additional threshold to activate the maximum speed of the cooling fan (P3 > 16 bars).

 

Pressure switch can be disassembled without emptying the system, and Schrader type valve protects the circuit against loss of the refrigerant.

 

The main failures observation linked with pressure switch:

Fan is turned on permanently or does not turn on at all

• Too high pressure in the system 
• Fan defect/failure
• Pressure switch microswitch failure
• Blown fan fuse
• Pressure sensor defect 

 

Compressor does not turn on, air conditioning does not work

• System without refrigerant
• Defective compressor clutch
• Pressure sensor defect