A/C Signal Circuits Check (Vehicle with A/C)

A/C Signal Circuits Check (Vehicle with A/C)










Troubleshooting

1. Check evaporator temp. sensor resistance.

Disconnect ECM connectors with ignition switch at OFF position.
Check resistance between terminals "G04-20" and "G04-18" and terminals "G04-6" and "G04-18".

At 0 °C 6.3 - 6.9 kohms
At 25 °C 1.8 - 2.2 kohms





Is it within specification?
YES
Go to Step 2.
NO
Faulty A/C evaporator temp. sensor or its circuit.

2. Check A/C switch signal.

Check voltage at terminal "G04-28" under each condition given as follows.

Ignition switch ON A/C switch OFF: 10 - 14 V
Ignition switch ON A/C switch ON: 0 - 1 V

Is check result as specified?
YES
Go to Step 3.
NO
"GRN/BLK" wire open or short
Poor "G04-28" terminal connection
If wire and connection are OK, substitute a known-good ECM and recheck.
Go to Step 3.

3. Check A/C condenser fan control system.

Is A/C cooling fan started when A/C switch and heater blower switch turned ON?
YES
Go to Step 7.
NO
Go to Step 4.

4. Check A/C condenser fan control relay and its circuit.

Check voltage at terminal "G04-32" under each condition given as follows.

Ignition switch ON A/C switch OFF: 10 - 14 V
Ignition switch ON A/C switch ON: 0 - 1 V

Is check result satisfactory?
YES
Go to Step 5.
NO
"BLU/YEL" wire open or short
Poor G04-32 terminal connection
If wire and connection are OK, substitute a known-good ECM and recheck.
Go to Step 5.

5. Check A/C condenser fan control relay.

Turn ignition switch OFF and remove A/C condenser fan control relay (1).
Check for proper connection to relay at terminals "c" and "d".
If OK, check that there is continuity between "c" and "d" when battery is connected to terminals "a" and "b".






Is check result satisfactory?
YES
Go to Step 6.
NO
Replace A/C condenser fan control relay.

6. Check A/C condenser fan.

Turn ignition switch OFF.
Disconnect A/C condenser fan motor connector (1).
Check for proper connection to motor at "RED/BLU" and "BLK" terminals.
If OK, connect battery to motor and check for operation.






Is it in good condition?
YES
"RED/BLU" or "BLK" circuit open.
NO
Replace A/C condenser fan motor.

7. Check A/C compressor control system.

Is A/C compressor started when A/C switch and heater blower switch turned ON while engine running?
YES
A/C control system is in good condition.
NO
Go to Step 8.

8. Check voltage at "C45-21" terminal under each condition given as follows.

While engine running
A/C switch OFF: 10 - 14 V
A/C switch ON: 0 - 1 V

NOTE:
When A/C evaporator thermistor temp. is below 2.5 °C (36.5 °F), A/C remains OFF ("C45-21" terminal voltage becomes 0 - 1 V). This condition is not abnormal.

Is check result satisfactory?
YES

NO
"BRN/YEL" wire open or short.
Poor "C45-21" terminal connection.
If wire and connection are OK, substitute a known-good ECM and recheck.
Go to Step 9.

9. Check A/C compressor control relay.

Turn ignition switch OFF and remove A/C compressor control relay (1).
Check for proper connection to relay at terminals "c" and "d".
If OK, check that there is continuity between "c" and "d" when battery is connected to terminals "a" and "b".






Is check result satisfactory?
YES
Check A/C compressor referring to Compressor Removal and Installation.
NO
Replace A/C compressor control relay.