Chevrolet Light Duty Truck 1973 Service Manual page 76

1A-50 HEATER A N D AIR C O N D IT IO N IN G
The following procedure can be used to quickly determine whether or not an air conditioning system has a proper charge
of refrigerant. This check can be made in a manner of minutes thus facilitating system diagnosis by pinpointing the problem
to the amount of charge in the system or by eliminating this possibility from the overall checkout.
C-K Models
1. Engine must be warm (thermostat open).
2. Hood and body doors open.
3. Selector lever set at A/C.
4. Temperature lever at first detent to the right of COLD (set
for outside air).
5. Blower on HI.
6. Engine idling at 1000 RPM.
7. Feel temperature of evaporator inlet and accumulator out­
let pipes with compressor engaged (fig. 52).
a. If both are cold this is a proper condition.
b. If inlet pipe is cooler than outlet pipe, system is low on
charge.
• Add a slight amount of refrigerant until both pipes
feel the same (system stabilized — 3-5 minutes).
• Then add 15 oz. (1 can) additional refrigerant.
REFRIGERANT QUICK-CHECK PROCEDURE
G Models and Motor Home Chassis Units
Start engine and place on fast idle. Set controls for
maximum cold with blower on high.
Bubbles present in sight
glass. ?
System low on charge.
Check with leak detector.
Correct leak, if any, and
fill system to proper
charge.
r 11— 1 1
No appreciable tempera­
ture differential 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.
r 1 " "1 . ...
If refrigerant in sight glass
remains clear for more
than 45 seconds (before
foaming and then settling
away from sight glass) an
overcharge is indicated.
Verify with a performance
check.
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.
I
Even though a differential
is noted, there exists a
possibility of overcharge.
An overfilled system will
result in poor cooling dur­
ing low speed operation
(as a result of excessive
head pressure). An overfill
is easily checked by dis­
connecting 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 refrigerant in
system. Continue checking
out system using perfor­
m ance checks outlined
previously.
LIGHT DUTY TRUCK SERVICE MANUAL