Checking the A/C System
CHECKING THE A/C SYSTEMGeneral
^ This fault tracing procedure applies only to that part of the A/C system which is regulated by Motronic 4.3 ECM.
^ For other fault tracing procedures, see Heating and Air Conditioning.
Preconditions
^ DTCs absent.
^ The fault is permanent.
Fault Sources
^ 15-supply short circuited to ground.
^ Break in 15-supply.
^ Break in lead between A/C relay and A/C switch, blower switch, control module or pressostat.
^ Break in lead between pressostat and compressor.
^ Faulty A/C relay, A/C switch, blower switch, pressostat or compressor clutch.
TESTING PROCEDURE
Preliminary Check
^ START the engine.
^ A/C switch ON.
^ Blower at low speed.
^ Note what the Scan Tool displays regarding the A/C compressor and A/C relay.
^ Compare the values with the following table to continue fault tracing.
Checking the Fuse
^ Remove fuse 31 and check that it is intact.
If the fuse is OK:
- Check the signal lead.
If the fuse has blown:
- Check the circuit for signs of short circuiting to ground.
Checking the Signal Lead
^ Connect the break-out box and check the ground connections.
^ Remove the glove box.
^ Disconnect the A/C relay (2/22).
^ Connect an ohmmeter between relay base terminal 4 and #40 (ECM B40) on the break-out box.
The ohmmeter should show approx. 0 Ohms.
If the reading is OK:
- Check the voltage supply to relay base terminal 1.
If the ohmmeter shows infinite resistance:
- Check the lead between ECM B40 and relay base terminal 4 for signs of a break.
Checking the Voltage Supply to Relay Base Terminal 1
^ A/C switch ON.
^ Ignition ON.
^ A/C relay disconnected.
^ Connect a voltmeter between relay base terminal 1 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Check the voltage supply to relay base terminal 2.
If the reading is incorrect.
- With ECC: Check the lead between fuse 31 and A/C relay (2/22) connector 1 for signs of a break.
- With MCC: Check the voltage supply from A/C switch.
Checking the Voltage Supply From A/C Switch
^ Ignition OFF.
^ Remove the heater controls.
^ A/C switch ON.
^ Ignition ON
^ Connect a voltmeter between A/C switch (3/54) connector 2 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Check the lead between A/C switch connector 2 and A/C relay connector 1 for signs of a break.
If the reading is incorrect:
- Check the voltage supply to the A/C switch.
Checking the Voltage Supply to the A/C Switch
^ Ignition ON.
^ Connect a voltmeter between A/C switch connector 1 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Test with a new A/C switch.
If the reading is incorrect:
- Check the lead between fuse 31 and A/C switch connector 1 for signs of a break.
Checking the Voltage Supply to Relay Base Terminal 2
^ Ignition ON.
^ Blower at low speed.
^ A/C relay disconnected.
^ Connect a voltmeter between relay base terminal 2 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Check the A/C relay.
If the reading is incorrect:
- With ECC: Check the lead between A/C relay connector 2 and the ECC control module (4/30) ECM B11 for signs of a break.
- With MCC: Proceed to: Checking the Voltage Supply From the Blower Switch section below.
Checking the A/C Relay
^ Ignition OFF.
^ Connect the A/C relay.
^ Ignition ON.
^ A/C switch ON.
^ Blower at low speed.
^ START the engine and let it run at idling speed.
^ Connect a voltmeter between the underneath of the relay base terminal (2/22) connector 3 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Proceed to: Checking the Voltage Supply to the Pressostat section below.
If the reading is incorrect:
- Test with a new A/C relay.
Checking the Voltage Supply From the Blower Switch
^ Ignition OFF.
^ Remove the heater controls.
^ Blower at low speed.
^ Ignition ON.
^ Connect a voltmeter between blower switch connector B1 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Check the lead between blower switch connector B1 and A/C relay connector 2 for signs of a break.
If the reading is incorrect:
- Check the voltage supply to blower switch.
Checking the Voltage Supply to Blower Switch
^ Ignition ON.
^ Connect a voltmeter between blower switch connector A4 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Test with a new blower switch.
If the reading is incorrect:
- Check the lead between fuse 31 and blower switch connector A4 for signs of a break.
Checking the Voltage Supply to the Pressostat
^ Ignition OFF.
^ Disconnect the pressostat's (7/53) connector.
^ Blower at low speed.
^ A/C switch ON.
^ START the engine.
^ Connect a voltmeter between pressostat connector 1 and ground.
The voltmeter should show battery voltage.
If the reading is OK:
- Check the pressostat resistance.
If the reading is incorrect:
- Check the lead between relay (2/22) connector 3 and pressostat (7/53) connector 1 for signs of a break.
Checking the Pressostat's Resistance
^ Ignition OFF.
^ Pressostat disconnected.
^ Connect an ohmmeter between the pressostat's two connectors.
The ohmmeter should show approx. 0 Ohms.
If the reading is OK:
- Check the lead between pressostat (7/53) connector 2 and compressor (8/3) connector for signs of a break.
If the reading is incorrect:
- Check the pressure in the A/C system.
Checking the Voltage Supply to the Compressor
^ Ignition OFF.
^ Open up the compressor's single-pin connector.
^ Connect an ohmmeter between the engine block and the connector (compressor side).
If the ohmmeter shows approx. 0 Ohms:
- The compressor clutch is faulty, replace clutch.
If the ohmmeter shows 2 - 5 Ohms:
- Check the lead between pressostat (7/53) connector 2 and the compressor's connector for signs of a break.
If the ohmmeter shows infinite resistance:
- The thermoswitch or the compressor clutch is faulty.
- Rectify as necessary.