Chrysler DODGE D150 1993 Service Manual page 1451

24 - 14 HEATING AND AIR CONDITIONING
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Fig. 9 Vacuum Actuator Test
terfere with the proper operation of the air
conditioning and heating controls at high speeds and
during acceleration.
COMPRESSOR NOISE
Noises t h a t develop during air conditioning opera­
tion can often be misleading.
FOR EXAMPLE: What sounds like a failed front
bearing or connecting rod, may be caused by loose
bolts, nuts, mounting brackets or a loose clutch as­
sembly.
Improper belt tension is also often the source of an
objectionable noise and can easily be mistaken for in­
ternal compressor troubles.
Drive belts are speed sensitive. That is, at different
engine speeds, and depending upon belt tension, belts
can develop unusual noises t h a t are often mistaken
for mechanical problems within the compressor.
The adjustment procedures follows:
(1) Select a quiet area for testing. Switch compres­
sor on and off several times to clearly identify com­
pressor noise.
(2) Tighten all compressor mounting bolts, clutch
mounting bolt, clutch coil mounting screws and com­
pressor drive belts. Check t h a t plumbing is not rub­
bing other parts.
(3) Make sure t h a t matched drive belts are in
equal tension. Replace any parts t h a t are defective or
missing.
(4) Test the vehicle. If noise persists, continue
trouble shooting system for source of noise.
Refer to A/C Compressor and Clutch Diagnosis
Charts.
CLUTCH COIL TEST
(1) Verify battery state of charge (test indicator
should be green.)
(2) Connect an ammeter (0-10 ampere scale) in se­
ries with the clutch coil terminal. Use a voltmeter
(0-20 volt scale) with clip leads measuring voltage
across the battery and A/C clutch.
(3) With A/C control in A/C mode and blower at
low speed, start the engine and r u n at normal idle.
(4) The A/C clutch should engage in 11 seconds af­
ter the start. The clutch voltage should be within 2
volts of the battery voltage. If the A/C clutch does
not engage, check the fuse.
(5) The A/C coil is acceptable, if the current draw
is 2.0 to 3.7 amperes at 11.5 to 12.5 volts. The test
room temperature should be 18°C to 24°C (65°F to
75°F). Where voltage is more t h a n 12.5 volts, add
electrical loads as needed by increasing blower speed
and/or switching other electrical accessories on. If
coil current reads zero, the coil is open and should be
replaced. If the ammeter reading is 4 amperes or
more, the coil is shorted and should be replaced. If
the coil voltage is not within 2 volts of the battery
voltage, check the circuit external to the clutch coil
for excessive voltage drop and repair accordingly.
Refer to A/C Compressor and Clutch Diagnosis
Charts.