Chapter 8 -Troubleshooting & Service Procedures
An expansion valve malfunction could mean the
Cause:
valve is stuck in the closed position, the filter
screen is clogged (block type expansion valves do
not have filter screens), moisture in the system has
frozen at the expansion valve orifice, or the sens-
ing bulb is not operating. In vehicles where the
TXV and sensing bulb are accessible, perform the
following test. If not accessible, then proceed to
Repair Procedure.
1. Warm diaphragm and valve body in your hand or
Test:
carefully with a heat gun. Activate system and
watch to see if the low pressure gauge rises.
2. Next, carefully spray a little nitrogen, or any sub-
stance below 32 degrees Fahrenheit, on the capil-
lary 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 part way 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.
3. Clean the surfaces of the evaporator outlet and the
capillary coil or bulb. Make sure the coil or bulb is
securely clamped to the evaporator outlet tube and
the insulation is in place. Next proceed with recov-
ering refrigerant from the system.
Repair Procedure:
Inspect the expansion valve screen (except block
type valves). To do this you must recover all refrig-
erant from the system. Disconnect the inlet hose
fitting from the expansion valve. Remove, clean
and replace the screen, then reconnect the hose.
Any signs of contamination will require flushing
the system. Next, replace the receiver-drier. Then
evacuate and recharge the system with refriger-
ant, and check AC operation and performance.
8-14
