20 - 7
Air Conditioning
Binary Pressure Switch Testing
The binary pressure switch assembly comprises a low
pressure switch designed to open at 1.96 bar (28.4 lbf/in
2
)
and a high pressure switch designed to open at
27.5 bar (400 lbf/in
2
)
When the refrigerant pressure is within the 1.96 and 27.5 bar
limits the switches will be closed and providing the freeze
protection thermostat and ON/OFF switches are closed, a
current will be supplied to the field coil of the clutch.
Through electro- magnetic action the field coil clutch will be
pulled towards the compressor's clutch and the refrigeration
cycle will commence.
If the fault finding table indicates that the pressure switch
assembly is defective the fault may be electrical or due to
incorrect system pressure.
Refer to
Checking Refrigerant Charge Level
. If the
refrigerant charge level is OK use the following electrical test
procedures.
1
Switch the engine off so that the air conditioning
system cannot operate.
2
Disconnect the binary pressure switch harness from the
side console harness and connect an external 12V
power supply between the pressure switch harness
connector and chassis. 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 in
the assembly is faulty or the level of refrigerant charge
is insufficient to close the low pressure switch.
3
Replace the pressure switch assembly. Refer to
Binary
Pressure Switch - Removal and Replacement
. If the
clutch still fails to operate check all electrical
connections.
Section B
9803/3280
Section B
20 - 7
Issue 1
Service Procedures
