Maintenance And Adjustments - GMC 1976 ZEO 6083 Maintenance Manual

1- 6 2 AIR CONDITIONING SYSTEM
Bubbles present in sight glass.
System low on charge . Check with
leak detector . Correct leak, if
any, and fill system to proper
charge .
No appreciable temperature dif-
ferential noted at compressor .
System empty or nearly empty.
Turn off engine and connect
Charging Station. Induce 1/2# of
refrigerant in system (if system
will not accept charge, start
engine and draw 1/2# in through
low pressure side). Check system
with leak detector .
If refrigerant in sight glass
remains clear for more than 45
seconds (before foaming and then
setting away from sight glass)
an overcharge is indicated.
Verify with a performance check.
The system makes use of a thermostatic switch
with an air sensing capillary. This capillary controls
the switch by sensing the temperature of the air leav-
ing the fins .
CHECKING FOR PROPER OPERATION
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.
a. 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 .
b. 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. Re-
place the switch .
c. Check the switch adjusting screw for
stripped or otherwise damaged threads.
No bubbles. Sight glass clear.
System is either fully charged or empty. Feel high
and low pressure pipes at compressor. High pressure
pipe should be warm ; low pressure pipe should be
cold .
Temperature differential noted at compressor .
Even though a differential is noted, there exists
a possibility of overcharge . An overfilled
system will result in poor cooling during low speed
operation (as a result of excessive head pressure),
An overfill is easily checked by disconnecting the
compressor clutch connector while observing the
sight glass.
If refrigerant foams and then settles away from
sight glass in less than 45 seconds, it can be
assumed that there is a proper charge of re-
frigerant in system . Continue checking out system
using performance checks outlined previously .
MAINTENANCE AND ADJUSTMENTS
THERMOSTATIC SWITCH
ADJUSTING SWITCH
If, after the above checks, the switch seems to be
operating properly, adjust for proper setting if neces-
sary, as follows:
1 . Vehicle must be set up as described in "Per-
formance 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 "General
Repair Procedures" section.
4. Remove the switch non-metal end plate to gain
access to the switch adjusting screw.
5 . If the outlet temperature was less than the
prescribed temperature at the end of each cooling
cycle, turn the adjusting screw a partial turn counter
clockwise (figure 30). If the outlet temperature was
more than prescribed temperature, turn the adjust-
ing screw clockwise.
NOTE:
One turn of the adjusting screw will