Komatsu 830E-AC Shop Manual page 967

PROBLEM: Air and/or Moisture in the System
Indications:
Low side pressure - HIGH
High side pressure - HIGH
Discharge air is only slightly cool.
Possible Causes
- Leaks in system.
PROBLEM: Expansion Valve Stuck or Plugged
Indications:
Low side pressure - VERY LOW or in a Vacuum
High side pressure - HIGH
Discharge air only slightly cool.
Expansion valve body is frosted or sweaty.
Possible Causes
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
frozen at the expansion valve orifice, or the
sensing bulb is not operating. If the sensing bulb
is accessible, perform the following test. If not,
proceed to the Repair Procedure.
N04031 10/06
Suggested Corrective Actions
Test for leaks, especially around the compressor
shaft seal area. After leaks are found, recover
refrigerant from the system and repair leaks. Re-
place the receiver-drier. Check the compressor
and replace any oil lost due to leakage. Evacuate
and recharge the system using a scale to ensure
proper quantity. Check A/C operation and perform-
ance.
Suggested Corrective Actions
Test: Warm diaphragm and valve body with your
hand, or very carefully with a heat gun. Activate
the system and watch to see if the low pressure
gauge rises. Next, carefully spray a little nitrogen,
or any substance below 32° F, on the capillary coil
(bulb) or valve diaphragm. The low side gauge
needle should drop and read at a lower (suction)
pressure on the gauge. This indicates the valve was
partially open and that your action closed it. Repeat
the test, but first warm the valve diaphragm 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,
remove all refrigerant from the system. Disconnect
the inlet hose fitting from the expansion valve.
Remove, clean, and replace the screen. Reconnect
the hose and replace the receiver-drier. Evacuate
and recharge the system with refrigerant using a
scale. Check AC operation and performance. If the
expansion valve tests did not cause the low press-
ure gauge needle to rise and drop, and if the other
procedure described did not correct the problem,
the expansion valve is defective. Replace the valve.
Operator Comfort N4-41