TRUCK SERVICE MANUAL
BODIES AND CABS
COMPRESSOR DRIVE BELT ALIGNMENT AND. TENSION
alignment and tension should be checked prior to the air
conditioning season and at least three or four times during the
Inspect drive belt(s) and replace if worn or damaged.
Check belt and pulley alignment and make any
Using belt tension gauge, check belt tension mid-way
between the compressor pulley and driving pulley.
For specified belt tension, see SPECIFICATIONS.
Belt tension adjustment procedures vary between
engine models. Some installations require movement of the
compressor on its mounting to adjust belt tensions. Some
have adjustment screws to manipulate the compressor for belt
adjustment. Others require movement of the alternator.
Certain precautions must be observed when
servicing the air conditioning system. (See
SAFETY PRECAUTIONS and also "Service
Hints" under COMPONENT REMOVAL AND
Heater and Defroster
With heater control (HTR) lever and blower switch
temperature is obtained.
With engine warmed up, heater inlet hose should feel
hot to the touch and heater outlet hose should feel
cool (or only slightly warm). If both hoses are hot,
check for a faulty or mis-adjusted heater control
cable or a faulty water flow control valve.
Set heater controls for maximum heat (HTR lever on
"HOT", blower switch on "HIGH") and operate engine
and heater for a few minutes to permit system to
normalize. Both inlet and outlet heater hoses should
flow from heater outlets. If neither hose feels hot or if
only the inlet hose is hot, refer to "No Heat" in
TROUBLE SHOOTING GUIDE.
Manipulate AIR CONTROL lever between "DEF" and
"CAB" positions and check for warm air flow from
defroster and heater outlets. If air flow is not correct
in relation to lever position, check for faulty or mis-
adjusted control cables or faulty air door seals.
Air Conditioning System
With air conditioning controls set for maximum
cooling, (A/C lever on "COLD", blower switch on
"HIGH"), operate engine and air conditioning system
for about five (5) minutes or until initial heat has been
removed from cab and an average flow of cold air is
If system does not cool, refer to "No Cooling" in TROUBLE
With system operating, feel all air conditioning
system components and refrigerant lines for proper
From the discharge side of compressor along high
pressure line, through condenser, filter-dehydrator
tank and up to expansion valve, everything should be
hot or warm to the touch. The expansion valve,
evaporator and all of the lines on the low pressure
side leading back to the compressor should be cool
to the touch. Any deviation from the above
conditions indicates a malfunction in the system.
A stoppage or severe restriction in the refrigerant
system can be located in this manner. Malfunctions
or stoppages may be indicated by extreme cold or
frosted areas (e.g., a cold filter-dehydrator tank
frosted part way up indicates a stoppage or serious
restriction in the tank).
Avoid contact with moving belts, pulleys and
fan when making this check. Beware of
extremely high temperatures at compressor
outlet (discharge) hoses and tubing.
CTS-2731 Page 20
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