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SYSTEM PERFORMANCE TEST
This test is performed to establish the condition of all
components in the system. Observe these conditions
during testing:
1. Start engine and operate at 1200 to 1500 RPM.
2. Place fan in front of condenser to simulate normal
ram air flow and allow system to stablize.
3. Place a thermometer in air conditioning vent clos-
est to evaporator.
4. Evaluate the readings obtained from the gauges
to see if they match the readings for the ambient
temperature.
As preliminary steps to begin checkout of the system,
perform the following:
1. Close all windows and doors to the cab.
2. Set air conditioning system at maximum cooling
and blower speed operation.
3. Readings on the two manifold gauges should be
within normal range, adjust for ambient tempera-
ture.
4. Compare evaporator discharge air temperature
reading to see if it matches the recommended
temperature for the ambient temperature and
gauge readings obtained.
5. Carefully feel the hoses and components on the
high side. All should be warm-hot to the touch.
Check the inlet and outlet of receiver-drier for even
temperatures, if outlet is cooler than inlet, a re-
striction is indicated.
Use extreme caution when placing hands on high
side components and hoses. Under certain condi-
tions these items can be extremely hot.
6. Feel the hoses and components on the low side.
They should be cool to the touch. Check connec-
tions near the expansion valve, inlet side should
be warm and cold-cool on the outlet side.
7. If these conditions are met, the system is consid-
ered normal. Shut down engine. Remove gauges
and install the caps on the service valves.
M09010 6/97
SYSTEM LEAK TESTING
Refrigerant leaks are probably the most common
cause of air conditioning problems, resulting from im-
proper or no cooling, to major internal component
damage. Leaks most commonly develop in two or
three places. The first is around the compressor shaft
seal, often accompanied by an indication of fresh re-
frigerant oil. If a system is not operated for a while
(winter months), the shaft seal may dry out and leak
slightly. The centrifugal force of the clutch pulley spin-
ning can also cause the problem. When the system is
operated and lubricant wets the seal, the leak may stop.
Such leaks can often be located visually, or by feeling
with your fingers around the shaft for traces of oil. (The
R-134a itself is invisible, odorless, and leaves no trace
when it leaks, but has a great affinity for refrigerant oil.)
A second common place for leaks is the nylon and
rubber hoses where they are crimped or clamped to
the fittings, or where routing allows abrasion. Other
threaded joints or areas where gaskets are used should
be visually and physically examined. Moving your fin-
gers along the bottom of the condenser and evapora-
tor, particularly near the drain hole for the condensate
will quickly indicate the condition of the evaporator.
Any trace of fresh oil here is a clear indication of a leak.
Usually, a 50% charged system is enough to find most
leaks. If the system is empty, connect the manifold
gauge set to the system and charge at least one (1) lb.
of refrigerant into the system.
Use extreme caution leak testing a system while
the engine is running.
In its natural state, refrigerant is a harmless, color-
less gas, but when combined with an open flame,
it will generate toxic fumes (phosgene gas), which
can cause serious injuries or death.
NOTE: The refrigerant is heavier than air and will move
down when it leaks. Apply pickup hose or test probe
on the undersurface of all components to locate leak.
Electronic leak detector
(Refer to Figure 9-4). As the test probe is moved into
an area where traces of refrigerant are present, a visual
or audible announcement indicates a leak. Audible
units usually change tone or speed as intensity
changes.
Air Conditioning System
for HFC 134a Refrigerant
M9-15
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Troubleshooting
