Checking the A/C System
CHECKING A/C SYSTEMGeneral
^ The fault-tracing procedure described below applies only to that section of the A/C system which is controlled by the Multiport Fuel Injection (MFI) and Distributor Ignition (DI) Systems.
Conditions
^ No DTCs present.
^ Fault is permanent.
Fault sources:
^ Busbar 15 supply short-circuited to ground.
^ Open-circuit in busbar 15 supply.
^ Open-circuit in lead between A/C relay and switch, blower switch, control module or high-pressure switch.
^ Open-circuit in lead between pressostat and compressor or high-pressure switch.
^ Faulty A/C relay, A/C switch, blower switch, high pressure switch, pressostat or compressor clutch.
TESTING PROCEDURE
Preliminary Check
^ START engine.
^ Switch ON A/C.
^ Operate blower at low speed.
^ Display MONITOR TEST, SCROLL DI and note status of A/C relay as indicated by Scan Tool (ST).
^ Display MONITOR TEST, SCROLL MFI and note status of A/C compressor as indicated by Scan Tool (ST).
Compare indications with those in table to continue fault tracing.
Checking Fuse
^ Remove fuse No. 31 and check that it is intact.
If fuse is intact:
- Proceed to: Checking Signal Lead.
If fuse is faulty:
- Check circuit for short circuit to ground.
Checking Signal Lead
^ Switch OFF ignition.
^ Remove glove compartment.
^ Unplug A/C relay (2/22).
^ Connect ohmmeter between relay base terminal 4 and ground.
Instrument should indicate approx. 5K Ohms.
If reading is correct:
- Proceed to: Checking Supply to Relay Base Terminal 1.
If reading is incorrect:
- Check lead between ICM B28 and relay base terminal 4 for open circuit.
Checking Supply to Relay Base Terminal 1
^ Switch ON A/C.
^ Switch ON ignition.
^ Unplug A/C relay.
^ Connect voltmeter between relay base terminal 1 and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Proceed to: Checking Supply to Relay Base Terminal 2, section below.
If reading is incorrect.
- ECC equipped cars:
Check lead between fuse No. 31 and A/C relay (2/22) terminal 1 for open-circuit.
- MCC equipped cars:
Proceed to: Checking Supply From A/C Switch.
Checking Supply From A/C Switch.
^ Remove blower control panel.
^ Switch ON A/C.
^ Switch ON ignition.
^ Connect voltmeter between A/C switch (3/54) terminal 2 and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Check lead between A/C switch terminal 2 and A/C relay terminal 1 for open circuit.
If reading is incorrect:
- Proceed to: Checking Supply to A/C Switch.
Checking Supply to A/C Switch.
^ Switch ON ignition.
^ Connect voltmeter between A/C switch terminal 1 and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Try with new A/C switch.
If reading is incorrect:
- Check lead between fuse 31 and A/C switch terminal 1 for open circuit.
Checking Supply to Relay Base Terminal 2
^ Switch ON ignition.
^ Run blower at low speed.
^ Unplug A/C relay.
^ Connect voltmeter between relay base terminal 2 and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Proceed to: Checking A/C Relay.
If reading is incorrect:
- ECC equipped cars:
Check lead between A/C relay terminal 2 and ECC ECM (4/30) B11 for open circuit.
- MCC equipped cars:
Proceed to: Checking Supply From Blower Switch, section below.
Checking A/C Relay
^ Switch ON ignition.
^ Plug in A/C relay (if unplugged).
^ Switch ON A/C.
^ Run blower at low speed.
^ START engine and allow to idle.
^ Connect voltmeter between terminal 3 on underside of relay base (2/22) and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Proceed to: Checking Supply to High-Pressure Switch.
If reading is incorrect:
- Try with new A/C relay
Checking Supply to High-Pressure Switch
^ START engine and allow to idle.
^ Run blower at low speed.
^ Switch ON A/C.
^ Undo high-pressure switch connector (C/EB).
^ Connect voltmeter between connector terminal 4 (car wiring harness side) and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Proceed to: Checking Resistance of High-Pressure Switch.
If reading is incorrect:
- Check lead between relay (2/22) terminal 3 and switch connector (C/EB) terminal 4 for open-circuit.
Checking Resistance of High-Pressure Switch
^ Switch OFF ignition.
^ Undo high-pressure switch connector (C/EB).
^ Connect ohmmeter between connector terminals 3 and 4 (on high-pressure switch side).
Instrument should indicate approx. 0 Ohms.
If reading is correct:
- Check lead between switch terminal 3 and pressostat (7/53) terminal 1 for open-circuit.
If reading is incorrect:
- Check A/C system pressure.
Checking Supply From Blower Switch
^ Remove heater control panel.
^ Run blower at low speed.
^ Switch ON ignition.
^ Connect voltmeter between blower switch terminal 1B and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Check lead between blower switch terminal 1B and A/C relay terminal 2 for open-circuit.
If reading is incorrect:
- Proceed to: Checking Supply to Blower Switch.
Checking Supply to Blower Switch
^ Switch ON ignition.
^ Connect voltmeter between blower switch terminal 4A and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Try with new blower switch.
If reading is incorrect:
- Check lead between fuse 31 and blower switch terminal 4A for open circuit.
Checking Supply to Pressostat
^ Switch ON ignition.
^ Run blower at low speed.
^ Switch ON A/C.
^ START engine.
^ Disconnect pressostat (7/53) connector.
^ Connect voltmeter between connector terminal 1 and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Proceed to: Checking Pressostat Resistance.
If reading is incorrect:
- Check lead between high-pressure switch (7/83) connector terminal 3 and pressostat (7/53) connector terminal 1 for open-circuit.
Checking Pressostat Resistance
^ Switch OFF ignition.
^ Disconnect pressostat connector.
^ Connect ohmmeter between both pressostat terminals.
Instrument should indicate approx. 0 Ohms.
If reading is correct:
- Check lead between pressostat (7/53) connector terminal 2 and compressor (8/3) connector for open-circuit.
If reading is incorrect:
- Check A/C system pressure.
Checking Supply to Compressor
^ Switch OFF ignition
^ Undo compressor single-pin connector.
^ Connect ohmmeter between cylinder block and connector (compressor side).
If resistance is approx. 0 Ohms:
- Compressor clutch is faulty.
- Replace Compressor clutch.
If resistance is 2 - 5 Ohms.
- Check lead between pressostat (7/53) connector terminal 2 and compressor connector for open-circuit.
If resistance is infinite:
- Either compressor temperature switch or clutch is faulty.
- Repair as required.