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Home >> Volvo >> 1998 >> S70 L5-2.4L VIN 55 B5254S >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Symptom Related Diagnostic Procedures >> Idling Problems >> Engine Speed Dips When A/C Is Switched On >> Checking A/C Relay Signal and A/C Compressor Signal
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Checking A/C Relay Signal and A/C Compressor Signal





Checking The A/C Relay Signal
- Start the engine and idle it.
- A/C button on.
- Blower fan on.
- Select scrolling values.
- Read the A/C relay status.
- Is the A/C relay on?

Yes:
^ Proceed to test step below.

No:
^ Proceed to Checking The A/C Relay Signal Cable section below.





Checking The A/C Compressor Signal
- Start the engine and idle it.
- A/C button on.
- Blower fan on.
- Select scrolling values.
- Read off A/C compressor status while the compressor is running.
- Is the compressor on?

Yes:
^ Proceed to test step below.

No:
^ Proceed to Checking The A/C Compressor Signal Cable section below.





Cleaning Idle Air Control Valve Connector
- Clean and grease engine control module (ECM) and idle air control (IAC) valve connectors.
- Check if engine speed still dips.
- Do the fault symptoms persist?

Yes:
^ Try a new idle air control valve.

No:
^ Operation done.





Checking The A/C Compressor Signal Cable
- Ignition off.
- Connect the test box and check ground terminals.
- Connect engine control module.
- A/C button on.
- Blower fan on.
- Start engine
- Connect a voltmeter between # 6 (# B6) and # 28 (# B28) on the test box.
- When the compressor is running the voltmeter should read battery voltage.

If reading is OK:
^ The cause of the engine speed dipping was contact resistance in the engine control module connector. Clean and grease engine control module connector.

If reading is incorrect:
^ Check cable between # B6 and pressure switch (Pressostat) connector (7/53) terminal 2 for an open-circuit.





Checking The A/C Relay Signal Cable
- Ignition off.
- Connect the test box and check ground terminals.
- Connect engine control module.
- A/C button on.
- Blower fan on.
- Start engine.
- Connect a voltmeter between # 25 (# B25) and # 28 (# B28) on the test box.
- When the compressor is running the voltmeter should read battery voltage.

If reading is OK:
^ The cause of the engine speed dipping was contact resistance in the engine control module connector. Clean and grease engine control module connector.

If reading is incorrect:
^ Check cable between # B25 and pressure switch (Pressostat) connector (7/53) terminal 1 for an open-circuit.

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