Expansion Valve Stuck Open; System High Pressure Side Restriction - Komatsu 930E-2 Shop Manual

Expansion Valve Stuck Open

Indications:
Gauge Reading- Low Side High
High Side Normal
Air from vents in cab is warm or only
slightly cool.
Cause- The expansion valve is stuck open and/or the
capillary tube (bulb) is not making proper contact
with the evaporator outlet tube. Liquid refrigerant
may be flooding the evaporator making it impossible
for the refrigerant to vaporize and absorb heat nor-
mally. In vehicles where the expansion valve sensing
bulb is accessible, check the capillary tube for
proper mounting and contact with the evaporator
outlet tube. Then perform the following test if the
valve is accessible. If it is not, proceed to the Repair
Procedure.

System High Pressure Side Restriction

Indications:
Gauge Reading- Low Side Low
High Side Normal to High
Air from vents in the cab is only slightly
cool.
Look for sweat or frost on high side
hoses and tubing, and frost appearing
right after the point of restriction.
The hose may be cool to the touch near
the restriction.
Cause- There could be a kink in a line, or other re-
striction in the high side of the system.
M9-24
Test: Operate the AC system on it's coldest setting
for a few minutes. Carefully spray a little nitro-
gen or other cold substance, on the capillary
tube coil (bulb) or head of the valve.
The low pressure (suction) side gauge needle
should now drop on the gauge. This indicates
the valve has closed and is not stuck open. Re-
peat the test, but first warm the valve dia-
phragm by warming with hands.
If the low side gauge shows a drop again, the
valve is not stuck. Clean the surfaces of the
evaporator outlet and the capillary coil or bulb.
Make sure the coil or bulb is securely fastened
to the evaporator outlet and covered with insula-
tion material. Operate the system and check
performance.
Repair Procedure: If the test did not result in
proper operation of the expansion valve, the
valve is defective and must be replaced. Re-
cover all refrigerant from the system and re-
place the expansion valve and the
receiver-drier. Evacuate and recharge the sys-
tem with refrigerant, then check AC operation
and performance.
Repair Procedure: After you locate the defective
component containing the restriction, recover
all of the refrigerant. Replace the defective com-
ponent and the receiver-drier. Evacuate and re-
charge the system with refrigerant, then check
AC operation and performance.
Air Conditioning System
for HFC 134a Refrigerant
M09010 6/97