PROBLEM: Expansion Valve Stuck Open
Indications:
Low side pressure - HIGH
High side pressure - Normal
Air from vents in the cab seems warm
Possible Causes
Suggested Corrective Actions
PROBLEM: High Pressure Side Restriction
Indications:
Low side pressure - LOW
High side pressure - Normal to HIGH
Discharge air is only slightly cool.
Look for sweat or frost on high side hoses
Possible Causes
Suggested Corrective Actions
Kink in a line, collapsed hose liners, plugged
or only slightly cool.
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 imposs-
ible for the refrigerant to vaporize and absorb
heat normally. 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.
Test: Operate the AC system on it's coldest
setting for a few minutes. Carefully spray
nitrogen or another cold substance on the cap-
Repair Procedure: If the test did not result in
illary 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. Repeat the test,
but first warm the valve diaphragm 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 insulation
material. Operate the system and check perform-
ance.
proper operation of the expansion valve, the valve
is defective and must be replaced. Recover all
refrigerant from the system and replace the expan-
sion valve and the receiver-drier. Evacuate and
recharge the system with refrigerant using a
scale. Check AC operation and performance.
and tubing. The line will be cool to the touch
near the restriction.
receiver-drier or condenser, etc.
Repair Procedure: After you locate the defective
component containing the restriction, recover all
of the refrigerant. Replace the defective compo-
nent and the receiver-drier. Evacuate and recharge
the system with refrigerant, then check AC
operation and performance.
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