20 - 2
Air Conditioning
Pressure Switches
The 12V supply is fed from the thermostat to the
compressor clutch via the low and high pressure switches
which are wired in series.
The low pressure switch requires a minimum refrigerant
charge level to close its contact. The high pressure switch
requires the charge level to remain below the maximum limit
to keep its contact closed.
Both pressure switch contacts must be closed for the
compressor clutch to operate. If the compressor clutch will
not operate when air conditioning is selected, the fault may
be either electrical or system pressure.
Pressure Switch Testing
1 Switch the engine off so that the air conditioning
system cannot operate.
2 Disconnect the pressure switch harness from the main
vehicle harness and connect an external 12V power
supply to the pressure switch harness connector. If
both pressure switches are working correctly, and the
system is at the correct charge level, the compressor
clutch will operate.
If the compressor clutch does not operate with the
external power supply, one of the pressure switches is
faulty or the level of refrigerant charge is insufficient to
close the low pressure switch.
High Pressure Switch Testing
1 Disconnect the air conditioning harness male/female
connectors from the high pressure switch 1.
2 Connect an external 12V power supply to the harness
connector - wire 688. If the compressor clutch
operates, renew the high pressure switch.
If the clutch does not operate check the low pressure
switch.
Low Pressure Switch Testing
1 If the refrigerant charge level in the system is correct,
but the clutch will still not function, disconnect the air
conditioning harness male/female connectors from the
low pressure switch 2.
2 Connect an external 12V power supply to the harness
connector - wire 686. If the compressor clutch
operates, renew the low pressure switch.
Note: If both pressure switches operate correctly, check all
electrical connections and the compressor clutch relay.
Removal and Replacement
!!
WARNING
Goggles and rubber gloves must be worn when pressure
switches are removed or fitted. A small amount of
refrigerant is released which can be harmful to the skin
and eyes.
BF 1-10
Removal
1 Disconnect the electrical connections and unscrew the
pressure switch.
Replacement
Note: The high pressure switch has a red body, the low
pressure switch has a bronze body, both have 1/4 UNF
female threads.
1 Screw the pressure switch into the pressure switch port
and torque tighten sufficiently to form a gas-tight seal.
2 Run the air conditioning and check the pressure
switches for leaks. If any leaks are found, tighten the
pressure switch further until the leaking stops.
Section B Body & Framework
9803/7130
Section B
20 - 2
Issue 1
Service Procedures
S193171
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