Operation and maintenance manual

Section 260-0130
SM 1405 Rev 2 11-04
1
DESCRIPTION
Temperature Control Switch
A thermostat switch senses the temperature of the
evaporator and engages or disengages the
compressor clutch. The control for this switch is
located in the cab.
Compressor
The compressor is designed to compress vapour and
can be damaged by non-compressibles such as dirt,
moisture, liquid refrigerant (R-134a), etc. The
compressor draws vaporized R-134a from the
evaporator (which maintains the low pressure
necessary for proper evaporation) and compresses
the vapour to a high pressure, which is necessary for
condensation. The high pressure vapour then moves
into the condenser where heat can be radiated to
change the R-134a back to liquid.
Note: R-134a designates the type of refrigerant used
in heavy duty vehicle air conditioning systems.
Compressor Drive Clutch
The R-134a compressor systems use an electronically
actuated clutch to engage and disengage drive to the
compressor. The 'V' belt pulley is mounted on a bearing
and is free to rotate without turning the compressor
crankshaft any time electrical power is disconnected.
The compressor is not operating when the pulley is
freewheeling. The field coil is energized by supplying
electrical current to the exposed wire. The other end of
the coil winding is grounded to the compressor and
equipment frame. Energizing the coil creates a magnetic
force that locks the driven disk to the pulley and drives the
compressor.
Condenser
The purpose of the condenser is to radiate enough
heat energy from the compressed high pressure
vaporized R-134a so that the R-134a changes from
vapour to liquid. During normal operation all the high
pressure section of the system will be warm or hot, but
large quantities of heat should be radiating from the
condenser. Nothing should be permitted to stop or
Fig. 1 - Typical Air Conditioning Flow Diagram
SM - 2430
1 - Compressor
2 - Condenser
3 - Receiver Drier
4 - Expansion Valve
5 - Evaporator
OPERATORS COMPARTMENT - Air Conditioning
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