Pontiac Fiero 1988 Service Manual page 571

6E2-C10-2 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI)
c
B A
D
RELAY HARNESS
CONNECTOR
f 150
A/C
CLUTCH
DK/GRN 59
ECM
DK BLU 458
B3
LT BLU 67
W2
BLK/WHT
922
HIGH PRESSURE SWITCH
l f g T < ^ -
LOW PRESSURE SWITCH
LT GRN/BLK 901
A/C FUSE
B24
A/C REQUEST
A/C SIGNAL
FOR FAN
A/C CONTROL
L SWITCH.. „
IGN CKT
4-30-87
4-23-87
* 7 S 3 6 7 4 - 6 E A
C H A i T
C-10
A/C CLUTCH CONTROL
2.5L "P" SERIES (TBI)
Circuit Description:
When an A/C Mode is selected on the A/C control switch, ignition voltage is supplied to the compressor low
pressure switch. If there is sufficient A/C refrigerant pressure, the low pressure switch will be closed and
complete the circuit to the closed high pressure cut-off switch and to CKTs 67 and 901. The voltage on CKT 67
to the ECM is shown by the "Scan" tool as A/C request "ON" (voltage present), "OFF" (no voltage). When a
request for A/C is seen by the ECM, the ECM will ground CKT 458 of the A/C clutch control relay, the relay
contact will close, and current will flow from CKT 922 to CKT 59 and engage the A/C compressor clutch. A
"Scan" tool will show the grounding of CKT 458, as A/C clutch "ON". If voltage is seen by the ECM on CKT 901,
the cooling fan will be turned "ON".
Diagnostic Aids:
Both pressure switches are located on the high
side of the A/C System. The low pressure switch will
be closed at 40-47 psi and allow A/C clutch operation.
Below 37 psi, the low pressure switch will be open and
the A/C clutch will not operate.
At about 430 psi, the high pressure switch will
open to disengage the A/C clutch and prevent system
damage.
CKT 922 will have voltage when the ignition
switch and A/C control are "ON". The high and low
pressure switches are located at the rear of A/C
compressor.