energized, it magnetically draws the clutch into con-
tact with the 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.
The compressor clutch and coil are the only serviced
parts on the compressor.
The compressor clutch engagement is controlled by
several components: the heater-A/C mode control
switch, the electronic cycling clutch switch, the low
pressure cut-off switch, the high pressure cut-off
switch, the compressor clutch relay, and the Power-
train Control Module (PCM). The PCM may delay
compressor clutch engagement for up to thirty sec-
onds. Refer to Group 14 - Fuel System for more infor-
mation on the PCM controls.
COMPRESSOR CLUTCH RELAY
DESCRIPTION
The compressor clutch relay is an International
Standards Organization (ISO) micro-relay. The termi-
nal designations and functions are the same as a con-
ventional ISO relay. However, the micro-relay
terminal orientation (footprint) is different, the cur-
rent capacity is lower, and the relay case dimensions
are smaller than those of the conventional ISO relay.
OPERATION
The compressor clutch relay is an electromechani-
cal device that switches battery current to the com-
pressor clutch coil when the Powertrain Control
Module (PCM) grounds the coil side of the relay. The
PCM responds to inputs from the heater-A/C mode
control switch, the electronic cycling clutch switch,
the low pressure cut-off switch, and the high pres-
sure cut-off switch. See Compressor Clutch Relay in
the Diagnosis and Testing section of this group for
more information.
The compressor clutch relay is located in the Power
Distribution Center (PDC) in the engine compart-
ment. Refer to the PDC label for relay identification
and location.
The compressor clutch relay cannot be repaired
and, if faulty or damaged, it must be replaced.
CONDENSER
DESCRIPTION
The condenser is located in the air flow in front of
the engine cooling radiator. The condenser is a heat
exchanger that allows the high-pressure refrigerant
gas being discharged by the compressor to give up its
heat to the air passing over the condenser fins.
OPERATION
When the refrigerant gas gives up its heat, it con-
denses. When the refrigerant leaves the condenser, it
has become a high-pressure liquid refrigerant. The
volume of air flowing over the condenser fins is crit-
ical to the proper cooling performance of the air con-
ditioning system. Therefore, it is important that
there are no objects placed in front of the radiator
grille openings in the front of the vehicle or foreign
material on the condenser fins that might obstruct
proper air flow. Also, any factory-installed air seals or
shrouds must be properly reinstalled following radia-
tor or condenser service.
The condenser cannot be repaired and, if faulty or
damaged, it must be replaced.
ELECTRONIC CYCLING CLUTCH SWITCH
DESCRIPTION
The Electronic Cycling Clutch Switch (ECCS) is
mounted to the outboard side of the thermal expan-
sion valve in the engine compartment. A thermistor
probe within a capillary tube on the switch is
inserted into a well on the side of the expansion
valve filled with a thermally-conductive grease. This
arrangement allows the ECCS to monitor the tem-
perature of the expanded refrigerant entering the
evaporator.
OPERATION
The function of the ECCS is to prevent refrigerant
temperatures from becoming so low that condensa-
tion freezes on the evaporator fins. This condition is
referred to as evaporator icing. Evaporator icing
reduces air conditioning system air flow and cooling
performance.
The ECCS is connected in series electrically with
the heater-A/C mode control switch, the low pressure
cut-off switch and the high pressure cut-off switch
between ground and the Powertrain Control Module
(PCM). The ECCS will open when it monitors a
refrigerant temperature below about 2.9° C (37.2° F),
and will close again when the refrigerant tempera-
ture reaches about 4.3° C (39.7° F). The opening and
closing of the ECCS signals the PCM to cycle the
compressor clutch on and off through the compressor
clutch relay.
The ECCS is a factory sealed and calibrated unit
and cannot be adjusted or repaired. If faulty or dam-
aged, the ECCS must be replaced.
DN HEATING AND AIR CONDITIONING 24 - 5
DESCRIPTION AND OPERATION (Continued)
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