TRUCK SERVICE MANUAL
BODIES AND CABS
Determine that system is operating properly.
(See "Physical Checks" under SERVICE
Observe sight glass for bubbles (Fig. 33).
Sight glass should appear clear (no bubbles).
Bubbles indicate a low refrigerant charge.
Add refrigerant. (See "Adding Refrigerant to
System" under SERVICE OPERATIONS.)
Fig. 33 Sight Glass Indications
Shut off engine and check air conditioning system for
refrigerant leaks using an electronic leak detector.
Follow equipment manufacturer's instructions.
OFF SEASON CARE
It is a good practice to operate the heater
occasionally during the summer season. This will circulate
coolant through the heater core to remove any trapped air and
flush out possible accumulations of sediment.
An important facet of off-season care of the air
conditioning system is periodic operation of the unit.
Operating the unit for five minutes twice a month after engine
warm-up keeps the compressor seals lubricated. If the seals
dry out, they may crack and leak.
Also, if the system is not operated periodically, clutch
and compressor bearings could become brinnelled. This is
caused by the continual hammering effect on the bearing
surface in the same spot from normal vibration during vehicle
operation. Do not remove the compressor drive belt during
In general, the system will function with less trouble if
it is not permitted to remain idle over long periods.
AIR FILTER REPLACEMENT
The air conditioning system air filter element should
be replaced every year at the beginning of the operating
season. More frequent replacement may be required on
vehicles operated in dusty areas.
Replace air filter as follows:
Remove cover from right side of instrument panel.
Remove cover from heater/evaporator unit.
Remove seal mounting strip (with seal) from blower
housing (Fig. 34).
Remove old filter element.
Fig. 34 Replacing Air Filter
Install new filter element. Be sure arrow on element
frame points in direction of air flow (away from
Inspect seal and replace if damaged. Attach new
seal to mounting strip with weatherstrip adhesive.
Install seal mounting strip (with seal) on blower
CTS-2731 Page 19
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