A/C COMPRESSOR CLUTCH/
COIL
DESCRIPTION
The A/C compressor clutch assembly consists of a
stationary electromagnetic A/C clutch field coil with a
zener diode, a pulley bearing and pulley assembly,
and a clutch plate (Fig. 1). These components provide
the means to engage and disengage the A/C compres-
sor from the engine accessory drive belt.
The A/C clutch field coil and the pulley bearing
and pulley assembly are both retained on the nose of
the A/C compressor with snap rings. The clutch plate
is splined to the compressor shaft and secured with a
bolt.
OPERATION
The A/C compressor clutch components provide the
means to engage and disengage the compressor from
the engine serpentine accessory drive belt. When the
electromagnetic A/C clutch field coil is energized, it
magnetically draws the clutch plate into contact with
the clutch pulley and drives the compressor shaft.
When the coil is not energized, the pulley freewheels
on the clutch hub bearing, which is part of the pulley.
A zener diode is connected in parallel with the A/C
clutch field coil. This diode controls the dissipation of
voltage induced into the coil windings by the collaps-
ing of the electromagnetic fields that occurs when the
compressor clutch is disengaged. The zener diode dis-
sipates this induced voltage by regulating a current
path to ground. This arrangement serves to protect
other circuits and components from potentially dam-
aging voltage spikes in the vehicle electrical system
that might occur if the voltage induced in the clutch
coil windings could not be dissipated.
The A/C compressor clutch engagement is con-
trolled by several components: the heater-A/C con-
trols in the passenger compartment, the A/C pressure
transducer on the liquid line, the evaporator temper-
ature sensor on the A/C expansion valve, the power-
train
control
module
(PCM)
in
the
engine
compartment, and the A/C compressor clutch relay in
the integrated power module (IPM). The PCM may
delay compressor clutch engagement for up to thirty
seconds (Refer to 8 - ELECTRICAL/ELECTRONIC
CONTROL
MODULES/POWERTRAIN
CONTROL
MODULE - DESCRIPTION - PCM OPERATION).
DIAGNOSIS AND TESTING
A/C COMPRESSOR CLUTCH COIL
The A/C compressor clutch coil electrical circuit is
controlled by the powertrain control module (PCM)
through the A/C clutch relay. The A/C clutch coil can
be tested by either measuring cluch field coil resis-
tance or by measuring current draw. Begin testing of
a suspected compressor clutch coil problem by per-
forming the preliminary checks.
PRELIMINARY CHECKS
(1) If the A/C compressor clutch will not engage,
verify the refrigerant charge level (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
DIAGNOSIS
AND
TESTING
-
REFRIGERANT
CHARGE LEVEL). If the refrigerant charge level is
OK, go to Step 2. If the refrigerant charge level is not
OK, adjust the refrigerant charge as required.
(2) If the A/C compressor clutch still will not
engage, disconnect the headlamp and dash wire har-
ness connector for the A/C pressure transducer and
check for battery current at the connector with the
engine running and the A/C-heater control set to the
A/C mode. If OK, go to TESTS. If not OK, refer
toBody Diagnostic Procedures to perform further
diagnosis.
TESTS
(1) Verify the battery state of charge (Refer to 8 -
ELECTRICAL/BATTERY
SYSTEM/BATTERY
-
DIAGNOSIS AND TESTING).
(2) Connect an ammeter (0 to 10 ampere scale
selected) in series with the clutch coil feed terminal.
Connect a voltmeter (0 to 20 volt scale selected) to
measure voltage across the battery and the clutch
coil.
Fig. 1 A/C Compressor Clutch
1 - BOLT
2 - CLUTCH PLATE
3 - PULLEY AND BEARING
4 - FIELD COIL
5 - SNAP RING (2)
6 - SHIM
CS
CONTROLS - FRONT
24 - 13