Excessive Air And/Or Moisture In The System; Expansion Valve Stuck Or Plugged - Komatsu 930E-2 Shop Manual

Excessive Air and/or Moisture in the System

Indications:
Gauge Reading- Low Side High
High Side High
Air from the vents in the cab is only
slightly cool.
Cause- System contains excessive air and/or mois-
ture.

Expansion Valve Stuck or Plugged

Indications:
Gauge Reading- Low Side Low or Vac-
uum
High Side High
Air from vents in the cab is only slightly
cool.
The expansion valve body is frosted or
sweating.
Cause- An expansion valve malfunction could mean
the valve is stuck in the closed position, the filter
screen is clogged (block expansion valves do not
have filter screens), moisture in the system has fro-
zen at the expansion valve orifice, or the sensing
bulb is not operating. If the sensing bulb is accessi-
ble, perform the following test. If not then proceed to
the Repair Procedure.
M09010 6/97
Repair Procedure: Test for leaks, recover refriger-
ant from the system and repair the leak. De-
pending on the type of system, replace the
receiver-drier or accumulator. Check and re-
place any compressor oil lost due to leakage.
Evacuate and recharge the system, then check
AC operation and performance.
Test: Warm diaphragm and valve body with your
hand, or very carefully with a heat gun. Activate
system and watch to see if the low pressure
gauge rises.
Next, carefully spray a little nitrogen, or any sub-
stance below 32° F, on the capillary coil (bulb)
or valve diaphragm. The low side gauge needle
should drop and read at a lower (suction) pres-
sure on the gauge. This indicates the valve was
part way open and that your action closed it.
Repeat the test, but first warm the valve dia-
phragm or capillary with your hand. If the low
side gauge drops again, the valve is not stuck.
Repair Procedure: Inspect the expansion valve
screen (except block type valves). To do this, re-
move all refrigerant from the system. Discon-
nect the inlet hose fitting from the expansion
valve. Remove, clean and replace the screen,
then reconnect the hose. Replace the receiver-
drier. Then evacuate and recharge the system
with refrigerant, and check AC operation and
performance. If the expansion valve tests did
not cause the low pressure gauge needle to rise
and drop, and if the other procedure described
did not correct the problem, the expansion
valve is defective. Follow the procedure for com-
ponent replacement.
Air Conditioning System
for HFC 134a Refrigerant
M9-23