III-94
Note: If the expansion valve tests did not cause the low pressure
gauge needle to rise and drop, and if the other procedures
described did not correct the problem, the expansion
valve is defective. You must recover all refrigerant from
the system again, and replace the expansion valve and
receiver-drier. Evacuate and recharge the system with
refrigerant, then check AC operation and performance.
Expansion Valve (TXV) Stuck Open
Tip: Air from vents in the 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 evapora-
tor making it impossible for the refrigerant to vaporize and
absorb heat normally. In vehicles where the TXV and sens-
ing bulb are accessible, check the capillary tube for proper
mounting and contact with the evaporator outlet tube. Then
perform the following test. If the TXV is not accessible,
then proceed to Repair Procedure.
Test: 1. Operate the AC system on it·s coldest setting for a few
minutes. Carefully spray a little nitrogen or other cold
substance, on to the capillary tube coil (bulb) or head of
the valve.
2. 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 with your hand.
Manifold Gauge Set Readings
Figure 8-10
Gauge reading, expansion
valve (TXV) stuck open.
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