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

DIAGNOSIS PROCEDURE

Step	Action	YES	NO
1	Check evaporator temp. sensor resistance  Disconnect ECM connectors with ignition switch at OFF position. Check for proper connection to "G04-34", "G04-26" and "G04-15" terminals of ECM connector. If OK, measure resistance between "G04-34" terminal and "G04-15" terminal of ECM connector, between "G04-26" terminal and "G04-15" terminal of ECM connector. Evaporator temp. sensor resistance  At 0°C 6.3 - 6.9 kohm  At 25°C 1.8 - 2.2 kohm    Is it within specification?	Go to Step 2.	Faulty A/C evaporator temp. sensor or its circuit.
2	Check A/C switch signal  Remove ECM from vehicle body referring to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION and connect connectors to ECM. Check voltage between "G04-12" terminal and vehicle body ground under each condition given as follows. A/C switch signal  Ignition switch ON A/C switch OFF: 10 - 14 V  Ignition switch ON A/C and blower switch ON: 0 - 1 V  Is check result as specified?	Go to Step 3.	Faulty A/C pressure switch, HVAC control module or these circuit.
3	Check A/C condenser fan control system  Is A/C cooling fan started when A/C switch and heater blower switch turned ON?	Go to Step 7.	Go to Step 4.
4	Check A/C condenser fan control relay and its circuit  Check voltage at "C45-1" terminal of ECM connector under each condition given as follows. Voltage at "C45-1" terminal of ECM connector  Ignition switch ON A/C switch OFF: 10 - 14 V  Ignition switch ON A/C switch ON and blower switch: 0 - 1 V  Is check result satisfactory?	Intermittent trouble. Check for intermittent referring to INTERMITTENT AND POOR CONNECTION INSPECTION . If OK, go to Step 5.	Go to Step 2 to 11 of A/C CONDENSER FAN CONTROL SYSTEM INSPECTION . If OK, go to Step 5.
5	Check A/C compressor control system  Is A/C compressor started when A/C switch and heater blower switch turned ON while engine running?	Intermittent trouble. Check for intermittent referring to INTERMITTENT AND POOR CONNECTION INSPECTION . If OK, substitute a knowngood ECM and recheck.	Go to Step 6.
6	Check voltage at "C45-28" wire terminal of ECM connector under each condition given as follows. While engine running  A/C switch OFF: 10 - 14 V  A/C switch and blower switch ON: 0 - 1 V  NOTE: When A/C evaporator thermistor temp. is below 2.5°C (36.5°F), A/C remains OFF ("C45-28" terminal voltage becomes 10 - 14 V). This condition is not abnormal. Is check result satisfactory?	Intermittent trouble.	Go to Step 7. Check for intermittent referring to INTERMITTENT AND POOR CONNECTION INSPECTION . If OK, substitute a knowngood ECM and recheck.
7	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?	Go to Step 8.	Replace A/C compressor control relay.
8	Check A/C compressor control relay and its circuit  Disconnect connectors from ECM with ignition switch turned OFF. Measure resistance between "C45-28" terminal of ECM connector and vehicle body ground. Is resistance infinity?	Go to Step 9.	"BRN/YEL" wire shorted to ground.
9	Check A/C compressor control relay and its circuit  Measure voltage between "C45-28" terminal of ECM connector and vehicle body ground with ignition switch turned ON. Is voltage 0 - 1 V?	Go to Step 10.	"BRN/YEL" wire shorted to power supply circuit.
10	Check A/C compressor control relay and its circuit  Connect connectors to ECM with ignition switch turned OFF. Connect A/C compressor control relay to relay/fuse box. With ignition switch, A/C switch and blower switch turned ON, measure voltage between "C45-28" terminal of ECM connector and vehicle body ground. Is voltage 10 - 14 V?	Go to Step 11.	Open or high resistance wire in "BRN/YEL" circuit.
11	Check A/C compressor control relay and its circuit  Disconnect connector from A/C compressor with ignition switch turned OFF. Run engine and A/C switch and blower switch turned ON. Measure voltage between "WHT" wire terminal of A/C compressor connector and vehicle body ground. Is voltage 10 - 14 V?	Check A/C compressor referring to .	Open or high resistance wire in "WHT" circuit.