Chevrolet 1977 light duty truck, Service Manual

Page: 78 / 861

REFRIGERANT Q U IC K -C H EC K PROCEDURE
The following procedure can be used to quickly determ ine w hether or not an air conditioning system has a p roper charge
o f refrigerant. This check can be m ade in a m anner o f m inutes thus facilitating system diagnosis by pinpointing the problem
to th e am ount o f charge in th e system o r by elim inating this possibility from the overall checkout.
C-K Models
1. Engine m ust be warm (th erm o stat open).
2. H ood and body doors open.
3. Selector lever set at A/C.
4. T em perature lever at first d eten t to the right o f COLD (set
for outside air).
5. Blower on HI.
6. Engine idling at 1000 RPM.
7. Feel tem perature of evaporator inlet and accum ulator o u t­
let pipes with com pressor engaged (fig. 52).
a. If b o th are cold this is a p roper condition.
b. If inlet pipe is cooler than o u tlet pipe, system is low on
charge.
• A dd a slight am o u n t o f refrigerant until b o th pipes
feel th e same (system stabilized — 3-5 m inutes).
• Then add 15 oz. (1 can) additional refrigerant.
G M odels and M otor H om e Chassis Units
S tart engine and place on fast idle. Set controls for
m axim um cold w ith blow er on high.
Bubbles present in sight
glass.
System low on charge.
Check w ith leak d etector.
C orrect leak, if any, and
fill s y s te m to proper
charge.
No bubbles. Sight glass
clear.
S y s te m is either fully
charged or em pty. Feel
high a n d low p r e s s u r e
pipes at com pressor. High
pressure pipe should be
warm ; low pressure pipe
should be cold.
I""
No appreciable tem pera­
ture differential noted at
com pressor. |
System em pty or nearly
em pty. Turn o ff engine
a n d c o n n e c t Charging
Station. Induce 1 / 2 # of
refrigerant in system (if
system will n o t accept
charge, start engine and
draw 1 /2 # in through low
p r e s s u r e s i d e ) . Check
system w ith leak detector.
T e m p e ra tu re differential
noted at com pressor.
I
Even though a differential
is noted, there exists a
possibility o f overcharge.
An overfilled system will
result in po o r cooling du r­
ing low speed operation
(as a result o f excessive
head pressure). An overfill
is easily checked by dis­
connecting the com pressor
c l u t c h connector while
observing the sight glass.
I
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 w ith a perform ance
check.
If refrigerant foam s and
then settles away from
sight glass in less than 45
seconds, it can be assumed
th at there is a proper
charge of refrigerant in
system . C ontinue checking
out system using p erfor­
m a n c e checks outlined
previously.