III-93
Cause: An expansion valve malfunction could mean the 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 sensing 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.
Test: 1. Warm diaphragm and valve body in your hand or care-
fully 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 substance
below 32 degrees Fahrenheit, on the capillary 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 cap-
illary 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 recovering refrigerant
from the system.
Repair Procedure:
Inspect the expansion valve screen (except block type
valves). To do this you must recover all refrigerant from the
system. Disconnect the inlet hose fitting from the expan-
sion valve. Remove, clean and replace the screen, then re-
connect the hose. Any signs of contamination will require
flushing the system. Next, replace the receiverdrier. Then
evacuate and recharge the system with refrigerant, and
check AC operation and performance.
Troubleshooting & Service Procedures
To Next Page
Loading...
Need help?
General
