Refrigerant Quick-Check Procedure; Checking Oil; Checking Compressor Oil Charge - Chevrolet 10 1971 Series Chassis Service Manual

HEATER AND AIR CONDITIONING 1A-22

REFRIGERANT QUICK-CHECK PROCEDURE

The following procedure can be used to quickly de­
termine 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.
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.
I
No appreciable tempera­
ture differential noted at
compressor.
I
System empty or nearly
empty. Turn off engine
and connect charging sta­
tion. Induce 1/2# of re­
frigerant 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 (be­
fore foaming and then set­
tling away from sight
glass) an overcharge is
indicated. Verify with a
performance check.
under " Purging the System."
while performing the following operation.
2. After system has been purged, connect the vacuum
line to the vacuum pump, turn on pump and open
Vacuum Control Valve (3) - See "General Note"
under "Evacuating and Charging the System." Con­
tinue to run pump for 15 minutes after the system
reaches 28-29 inches vacuum.
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 dur­
ing low speed operation
(as a result of excessive
head pressure). An over­
fill is easily checked by
disconnecting the com­
pressor 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 as­
sumed that there is a
proper charge of refriger­
ant in system. Continue
checking out system using
performance checks out­
lined previously.
Refer to Figure 30
If 28-29 inches cannot be obtained,
NOTE:
close Vacuum Control Valve (3) and shut off
vacuum pump. Open Refrigerant Control Valve
(4) and allow 1/2 pound of R-12 to enter system.
Locate and repair all leaks.
pound and re-evacuate for 5 minutes.
3. Only after evacuating as above, is system ready for
charging. Note reading on sight glass of charging
cylinder. If it does not contain a sufficient amount
for a full charge, fill to the proper level.
4. With High and Low pressure Valves (1 and 2)
open, close Vacuum Control Valve (3) and open
Refrigerant Control Valve (4).
If the charge will not transfer com­
NOTE:
pletely from the station to the system, close
the high pressure valve at the gauge set, set
the air conditioning controls for cooling, check
that the engine compartment is clear of ob­
structions, and start the engine.
operation will decrease the low side pressure
in the system.
System is now charged and should be performance
tested before removing gauges.

CHECKING OIL

In the six cylinder compressor it is not recommended
that the oil be checked as a matter of course. Generally,
compressor oil level should be checked only where
there is evidence of a major loss of system oil such as
might be caused by:
• A broken refrigerant hose.
• A severe hose fitting leak.
• A very badly leaking compressor seal.
• Collision damage to the system components.
As a quick check on compressor oil charge, with the
engine off, carefully crack open the oil drain plug on the
bottom of the compressor.
pressor has the required amount of oil. To further check
the compressor oil charge, should the above test show
insufficient oil, it is necessary to remove the compressor
from the vehicle, drain and measure the oil.
The oil may appear foamy. This is con­
NOTE:
sidered normal.
To further check the compressor oil charge, should the
above test show insufficient oil, it is necessary to remove
the compressor from the vehicle, drain and measure
the oil as outlined under " Checking Compressor Oil
Charge/'

Checking Compressor Oil Charge

1. Run the system for 10 minutes at 500-600 engine
rpm with controls set for maximum cooling and high
blower speed.
2. Turn off engine, discharge the
compressor from vehicle, place it in a horizontal
position with the drain plug downward. Remove the
drain plug and, tipping the compressor back and
forth and rotating the compressor shaft, drain the
oil into a clean container, measure and discard the
oil.
3. a. If the quantity drained was 4 fluid oz. or more,
Purge this 1/2
Compressor
If oil comes out, the com­
system, remove
10-30 CHEVROLET TRUCK SERVICE MANUAL