High Pressure Sensor / Switch, HVAC

Stage 1:
Allows the compressor to work at temperatures
down to +0 °C (32 °F)
Pressure in the system at this temperature
is about 2 bar (29 psi)

Stage 2:
For R12 refrigerant starts the engine's electric radiator fan at a pressure
of about 15 bar (210 psi)
and disconnected
at 11 bar (155 psi)

For R134a refrigerant, the fan is started
at 16.5 bar (239 psi)
and disconnected
at 12.5 bar (181 psi)

Stage 3:
This is a safety feature which breaks the electrical circuit to the compressor if pressure exceeds:
for R12 refrigerant 27 bar (380 psi)
and reconnected when pressure is
below 6 bar (90 psi)

for R134a refrigerant the switch breaks
at 30 bar (435 psi)