Pontiac Fiero 1988 Service Manual page 1062

AIR CONDITIONING: COMPRESSOR CONTROLS
C60, M A N U A L
C: A / C C O M P R E S S O R F U N C T I O N
C O N T R O L T E S T
Measure: VOLTAGE
A t : A/C CONTROL HEAD CONNECTOR
(Connected)
Conditions:
• Ignition Switch: RUN (Engine need not
be running)
• A/C Mode: NORM
• Temperature Outside Car: ABOVE 60°F
(16°C)
Measure
Between
N (BRN) &
Ground
G (LT GRN) &
Ground
Correct
Voltage
Battery
Battery
For Diagnosis
S e e l
See 2
• If both voltages are correct, go to CI.
1. Check for open HTR A/C Fuse or open
BRN (50) wire.
2. Replace A/C Control Head.
CI. Measure the voltage at terminal A of the
A/C Compressor Control Relay with a fused
jumper connected across the terminals of
the Pressure Cycling Switch connector
(disconnected).
• If battery voltage is not present with the
jumper connected, check the wiring be-
tween the switches back to the A/C Con-
trol Head (see schematic).
• If battery voltage is present, refer to
Section IB to check for normal re-
frigerant charge. If refrigerant charge is
normal, replace the Pressure Cycling
Switch.
C I R C U I T O P E R A T I O N
The Compressor for the Air Conditioning
System is belt driven by the engine through the
A/C Compressor Clutch. The clutch allows the
Compressor to be disengaged when air condi-
tioning is not required, and also allows the air
conditioning load to be removed from the
engine when needed.
Operation of the Compressor depends on the
particular mode selected by the driver. When the
A/C Mode Selector is in MAX, NORM, BI-
LEVEL, or DEF, battery voltage is applied
through the HTR A/C Fuse and A/C Control
Head Selector to the A/C Compressor Control
Relay.
L4
VIN R
For vehicles equipped with the L4 VIN R
engine, the path to the A/C Compressor Control
Relay is through the A/C Low Pressure Switch
and the A/C High Pressure Cut-Out Switch,
which are both normally closed. The A/C Low
Pressure Switch opens if the refrigerant charge
is too low to operate the A/C Compressor with-
out possible damage to it. The A/C High Pres-
sure Cut-Out Switch opens when refrigerant
pressure is too high for normal operation.
The A/C Compressor Control Relay is oper-
ated by the ECM. When the ECM receives the
A/C On signal at terminal 2, it grounds terminal
3, energizing the Relay. When the Relay is
energized, voltage is applied to the A/C Com-
pressor Clutch through the contact of the relay.
If the ECM determines that engine load should
be reduced, such as during full throttle, the A/C
Compressor Control Relay is de-energized. This
removes voltage from the A/C Compressor and
removes the A/C load from the engine.
V6 VIN 9
The voltage path from the A/C Control Head is
through the Pressure Cycling Switch to the coil
of the A/C Compressor Control Relay. Voltage is
also applied to terminal B8 of the Electronic
Control Module (ECM). When the ECM receives
the voltage input at terminal B8, it will ground
terminal 02 to energize the A/C Compressor
Control Relay. The Pressure Cycling Switch
opens when the refrigerant pressure is less than
165 kPa (24 psi). It closes again when the pres-
sure rises enough to indicate that additional
cooling is required. This operation causes the
Compressor to cycle on and off so that the
evaporator temperature does not drop low
enough to cause icing.
When the A/C Compressor Control Relay op-
erates, it applies voltage from the A/C Power
Relay through its contacts to the A/C Com-
pressor Clutch. The ECM will remove the
ground at terminal C2 to de-energize the A/C
Compressor Control Relay when the air condi-
tioning load should be removed from the engine,
such as during wide open throttle.
The A/C Compressor Clutch is grounded
through the normally closed A/C High Pressure
Cut-Out Switch which opens if refrigerant pres-
sure rises too high.