Manifold Gauge Set Readings
If the expansion valve tests did not cause the
Note:
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 sys-
tem again, and replace the expansion valve and
receiver-drier. Evacuate and recharge the sys-
tem with refrigerant, then check AC operation
and performance.
Expansion Valve (TXV) Stuck Open
Figure 8-10
Gauge reading, expansion
valve (TXV) stuck open.
Air from vents in the cab is warm or only slightly
Tip:
cool.
The expansion valve is stuck open and/or the capil-
Cause:
lary 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 TXV and sensing 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.
1. Operate the AC system on it's coldest setting for a
Test:
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.
8-15
