Chapter 8 -Troubleshooting & Service Procedures
Heavy duty vehicle vibration causes stress on all lines, fittings and
connections. Regular maintenance includes checking and tightening any
suspect line, or hose retainers, or grommet position where the grommet is
protecting a line or hose from abrasion. Any insulating material wrapped
around hoses must be in place and securely fastened.
4. Refrigerant Metering Valves
When you consider valve problems there are obvious differences in valve
construction and what can go wrong. If a valve is clogged with sludge or
other obstruction, the result is a valve problem but the cause is contami-
nation in the system. Valves get stuck open or closed, although most often
closed when the gas charge is lost from the diaphragm housing in a
traditional TXV. The capillary tube can vibrate loose from the evaporator
outlet tube. The capillary can break and the small quantity of tempera-
ture sensitive gas can escape. The diagnosis of a valve as defective calls
for replacement.
5. Other Problems--Leaks, Moisture, and Adding Refrigerant
Before any refrigerant was put inside the AC system, someone used a
vacuum pump to evacuate any air and moisture. Vacuum is really a force
pulling against all hoses, fittings and components from the inside. When
the system is charged with refrigerant, the pressure goes from minus (a
vacuum) to plus pressure inside the hoses and all components. The
refrigerant and refrigeration oil are trying to escape from the system at
all times.
Technicians frequently add refrigerant to a system, replacing refriger-
ant seepage through system connections or fittings. If the system has
been maintained regularly (every three to six months), adding a small
amount of refrigerant may result in normal system function. However,
the best procedure is to check all connections and look for, find and repair
any leaks before adding refrigerant.
When your leak detector indicates the presence of a leak, you can't tell
how long the system has been leaking. Finding one leak doesn't mean
there are not others. Until you have some AC system work experience, it
will be hard to guess how much refrigerant may have leaked. If you have
to top a system off with a half pound of refrigerant or more, adding
refrigerant is not the answer.
Find the leak. Recover all of the refrigerant and repair the system. The
moisture absorbing capacity of any desiccant material is limited and
cannot be measured. For that reason, replace the receiver-drier or accu-
mulator. Then evacuate the system for an hour and recharge with refrig-
erant.
When a compressor shaft seal has leaked oil and the refrigerant charge
is a little low, the shaft seal may have leaked because the air conditioner
was not used. The seal can get a little out of round from the weight of the
crankshaft and leak above the shaft. Running the compressor may cause
the seal to swell and close up the leak. The shaft rotation exerts force all
around the seal and puts life back into it. To prevent this from happening,
manufacturers recommend regular AC system operation a minimum of
every couple of weeks even in cool weather.
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