WD Catalog 2018

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Chapter 8 – Troubleshooting & Service Procedures
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2. Condenser
Condensers get dirty and the dirt reduces heat movement by insulating
the condenser. The fittings come loose or break from stress if the con-
denser or connecting hoses are not secured properly to keep the effects of
vibration at a minimum.
Heat transfer efficiency and pressure in the condenser are affected by
the amount of outside air flowing through condenser fins. A lack of air flow
can mean the refrigerant doesn’t give up enough heat energy to the
outside air (it doesn’t change state). The refrigerant arrives at the evapo-
rator as a gas and can’t pick up any heat energy from cab air. In the cab,
air from the vents is only slightly cool or warm.
One possible cause of condenser malfunction could be the engine cool-
ing system. This is why fan clutches and radiator shutters are often
controlled or overridden by AC switch function. In fact, we can add fan
clutch, radiator shutters and also fan motors to condenser problems. If
they don’t function to allow sufficient air through the condenser, pressure
inside the system may become dangerously high. A lack of air through the
condenser fins can raise high side pressure and blow out the weakest
point in a system, or damage the compressor.
3. Refrigerant Lines, Hoses and Fittings
Problems with these parts may be caused by normal deterioration, vibra-
tion damage, lack of maintenance or human error (improper installation
or replacement). All rubber parts are attacked by ozone (oxygen) in the
air. Rubber parts break down slowly and become more vulnerable to the
effects of vibration with the passage of time.
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