Chevrolet Light Duty Truck 1973, Service Manual

Page: 77 / 979

HEATER A N D AIR C O N D IT I O N I N G 1A-51
Fig. 52-Checking Evaporator Inlet and Accumulator
Outlet Temperatures
M A IN TE N A N C E A N D ADJUSTMENTS
THERMOSTATIC SWITCH
All systems make use of a thermostatic switch with either
an air or fin sensing capillary. This capillary controls the
switch by sensing the temperature of the air leaving the
fins (G and Motor Home Units) or temperature of the
fins (C-K models).
Checking for Proper Operation
G and Motor Home Chassis Units
1. Install the gauge set and set up the vehicle as
described under "Performance Test."
2. Movement of the temperature control knob should
result in a definite change in suction pressure and
cycling of the compressor clutch.
• If compressor continued to operate regardless of
the knob adjustment, it indicates that the switch
points are fused which will lead to evaporator
freeze-up. Replace the switch.
• If the compressor does not operate, regardless of
the position of the knob, a loss of the power
element charge is indicated (provided that it has
been established that power is supplied to the
switch). This, of course, results in no cooling.
Replace the switch.
• Check the switch adjusting screw for stripped or
otherwise damaged threads.
C-K Models
1. Install the gauge set and set up the vehicle as
described under "Performance Test".
2. Set the control at A/C, HI blower, max COLD and
run the engine at 2000 rpm.
• The thermostatic switch should cycle the
compressor off when the low limit of the outlet
air temperature is reached (see Performance
Data). If it does not, the switch points are fused
which will lead to evaporator freeze up. Replace
the switch.
• If the compressor does not operate, a loss of
power element charge is indicated (provided that
it has been established that power is supplied to
the switch). This, of course, results in no cooling.
Replace the switch.
• Check the switch adjusting screw for stripped or
otherwise damaged threads.
Adjusting Switch
If, after the above checks, the switch seems to be
operating properly, adjust for proper setting if necessary,
as follows:
1. Vehicle must be set up as described in "Perform­
ance Test."
2. The suction side of the system, read on the low
pressure gauge, should pull down to the pressure
shown in the chart in "Performance Data" under
the ambient temperature at the time the switch is
being set.
3. Remove the switch as outlined in the "Component
Part Replacement" section of this manual.
4. Remove the switch non-metal end plate to gain
access to the switch adjusting screw.
LIGHT DUTY TRUCK SERVICE MANUAL