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Home >> Volvo >> 1998 >> V70 GL L5-2.4L VIN 55 B5254S >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Component Tests and General Diagnostics >> Other Electrical Fault Tracing >> Checking the A/C System

Checking the A/C System

Checking The A/C System

General
- This fault-tracing procedure applies only to that part of the A/C system regulated by the Motronic 4.4 engine control module (ECM).

Condition
- Diagnostic trouble codes (DTCs) absent
- Fault is permanent.

Possible Source(s)
- Short-circuit to ground in 15-supply
- Open-circuit in 15-supply
- Open-circuit in cable between A/C relay and A/C switch, blower switch, control module or pressure switch (Pressostat)
- Open-circuit in cable between pressure switch (Pressostat) and compressor.
- Defective A/C relay, A/C switch, blower switch, pressure switch (Pressostat) or compressor clutch.





Preliminary Check
- Start engine.
- A/C switch on.
- Blower fan at low-speed.
- Select scrolling values.
- Note Volvo Scan Tool (ST) reading for A/C compressor and A/C relay.

- Compare the A/C COMP A/C RELAY display parameters to continue fault-tracing.

Parameter
^ OFF OFF - Select Alternative 1
^ OFF ON - Select Alternative 2
^ ON ON - Select Alternative 3

- Select an alternative.

Alternative 1:
^ Proceed to Checking Fuse section below.

Alternative 2:
^ Proceed to Checking The Power Supply To The Pressure Switch (Pressostat) section below.

Alternative 3:
^ Proceed to Checking The Power Supply To The Compressor section below.





Checking Fuse
- Remove fuse 31 and check that it is intact.
- Is the fuse intact?

Yes:
^ Proceed to test step below.

No:
^ Check the circuit for a short-circuit to ground.





Checking Signal Cable
- Connect the test box and check ground terminals.
- Remove glove compartment.
- Disconnect the A/C relay (2/22).
- Connect an ohmmeter between relay base terminal 4 and on the test box # 40 (# B40).
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ Check cable between #B40 and relay base terminal 4 for an open-circuit.





Checking The Power 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 read battery voltage.

If reading is OK:
^ Proceed to Checking The Power Supply To Relay Base Terminal 2 section below.

If reading is incorrect:
^ If equipped with ECC: Check cable between fuse 31 and A/C relay (2/22) terminal 1 for an open-circuit.

^ If equipped with MCC: Proceed to test step below.





Checking The Power 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) terminal 2 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Check cable between A/C switch terminal 2 and A/C relay terminal 1 for an open-circuit.

If reading is incorrect:
^ Proceed to test step below.





Checking The Power Supply To The A/C Switch
- Ignition on.
- Connect a voltmeter between A/C switch terminal 1 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Try a new A/C switch.

If reading is incorrect:
^ Check cable between fuse 31 and A/C switch terminal 1 for an open-circuit.





Checking The Power Supply To Relay Base Terminal 2
- Ignition on.
- Blower fan at low-speed.
- A/C relay disconnected.
- Connect a voltmeter between relay base terminal 2 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ If equipped with ECC: Check cable between A/C relay terminal 2 and the ECC control module (4/30) # B11 for an open-circuit.

^ If equipped with MCC: Proceed to test step below.

If reading is OK:
^ Proceed to test step below.





Checking The A/C Relay
- Ignition off.
- Connect the A/C relay.
- Ignition on.
- A/C switch on.
- Blower fan at low-speed.
- Start the engine and idle it.
- Connect a voltmeter between the underneath of the relay base (2/22) terminal 3 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Proceed to Checking The Power Supply To The Pressure Switch (Pressostat) section below.

If reading is incorrect:
^ Try a new A/C relay.





Checking The Power Supply From The Blower Tan Switch
- Ignition off.
- Remove the heater controls.
- Blower fan at low-speed.
- Ignition on.
- Connect a voltmeter between blower fan switch terminal B1 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Check cable between blower fan switch terminal B1 and A/C relay terminal 2 for an open-circuit.

If reading is incorrect:
^ Proceed to test step below.





Checking The Power Supply To The Blower Fan Switch
- Ignition on.
- Connect a voltmeter between blower fan switch terminal A4 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Try a new blower fan switch.

If reading is incorrect:
^ Check cable between fuse 31 and blower fan switch terminal A4 for an open-circuit.





Checking The Power Supply To The Pressure Switch (Pressostat)
- Ignition off.
- Disconnect the pressure switch (Pressostat) (7/53) connector.
- Blower fan at low-speed.
- A/C switch on.
- Start engine.
- Connect a voltmeter between pressure switch (Pressostat) connector 1 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ Check cable between relay (2/22) terminal 3 and pressure switch (Pressostat) (7/53) terminal 1 for an open-circuit.





Checking The Pressure Switch (Pressostat) Resistance
- Ignition off.
- Pressure switch (Pressostat) disconnected.
- Connect an ohmmeter between both pressure switch (Pressostat) terminals.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Check cable between pressure switch (Pressostat) (7/53) terminal 2 and compressor (8/3) connector for an open-circuit.

If reading is incorrect:
^ Check pressure in A/C system.





Checking The Power Supply To The Compressor
- Ignition off.
- Open up the single-pin compressor connector.
- Connect an ohmmeter between the engine block and the connector (compressor side).

If the ohmmeter reads approx. 0 ohms.
^ Select Alternative 1.

If The ohmmeter reads 2 - 5 ohms:
^ Select Alternative 2.

If the ohmmeter reads infinite resistance:
^ Select Alternative 3.

- Select a suitable alternative.

Alternative 1:
^ The compressor clutch is faulty, replace clutch.

Alternative 2:
^ Check cable between pressure switch (Pressostat) (7/53) terminal 2 and compressor connector for an open-circuit.

Alternative 3:
^ Defective thermoswitch or compressor clutch. Remedy as necessary.
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