A/C Signal Circuit Troubleshooting
A/C Signal Circuit Troubleshooting
NOTE:
Do not use this troubleshooting procedure if any of the following items are operative with the A/C button and the fan control dial ON: The A/C condenser fan, the radiator fan, or the A/C compressor. Refer to the symptom troubleshooting index.
Do not use this troubleshooting procedure if the A/C system pressure is abnormal.
Before doing symptom troubleshooting, check for PGM-FI DTCs.
1.
PGM-FI system parameter check:

PGM-FI system parameter check
?1.
Connect the HDS to the DLC.

?2.
Turn the vehicle to the ON mode. Make sure the A/C system is OFF.

?3.
Check the parameter(s) below with the HDS.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
A/C SWITCH
OFF
      

Do the current condition(s) match the threshold?

     
YES
     
     
     
Go to step 2.
     
NO
     
     
     
Go to step 3.
2.
Shorted wire check (ACS line):

Shorted wire check (ACS line)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Disconnect the following connectors.
Under-dash fuse/relay box connector H (20P)
A/C switch 7P connector

?3.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Under-dash fuse/relay box connector H (20P): disconnected
A/C switch 7P connector: disconnected
Test point 1
A/C switch 7P connector No. 2
Test point 2
Body ground


Is there continuity?

     
YES
     
     
     
Repair a short to ground in the wire between the under-dash fuse/relay box and the A/C switch.?
     
NO
     
     
     
The ACS wire is not shorted. Replace the under-dash fuse/relay box.?
3.
Heater control system check:

Heater control system check
?1.
Start the engine.

?2.
Set the A/C button and the fan control dial to ON.

?3.
Check the parameter(s) below with the HDS.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
A/C SWITCH
ON
      
A/C CLUTCH
ON
      

Do the current condition(s) match the threshold?

     
YES
     
     
     
     
NO
     
     
     
A/C SWITCH is OFF, go to step 6.
     
NO
     
     
     
A/C SWITCH is ON and A/C CLUTCH is OFF, go to step 4.
4.
A/C pressure threshold check:

A/C pressure threshold check
?1.
Check the parameter(s) below with the HDS.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
A/C PRESSURE SENSOR
196?3,138
kPa
    
2.00?32.00
kgf/cm2
28.4?455.1
psi

Do the current condition(s) match the threshold?

     
YES
     
     
     
Go to step 5.
     
NO
     
     
     
5.
Evaporator temperature sensor check:

Evaporator temperature sensor check
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Jump the SCS line with the HDS.

NOTE: This step must be done to protect the PCM from damage.

?3.
Disconnect the following connector.
PCM connector A (51P)

?4.
Measure the resistance between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
PCM connector A (51P): disconnected
Test point 1
PCM connector A (51P) No. 39
Test point 2
PCM connector A (51P) No. 42

Is resistance less than 24 k??

     
YES
     
     
     
Update the PCM if it does not have the latest software, or substitute a known-good PCM, and recheck. If the symptom/indication goes away with a known-good PCM, replace the original PCM.?
     
NO
     
     
     
6.
Determine possible failure area (ACS line, others):

Determine possible failure area (ACS line, others)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Disconnect the following connector.
A/C switch 7P connector

?3.
Turn the vehicle to the ON mode.

?4.
Measure the voltage between test points 1 and 2.
Test condition
Vehicle ON mode
A/C switch 7P connector: disconnected
Test point 1
A/C switch 7P connector No. 2
Test point 2
Body ground


Is there battery voltage?

     
YES
     
     
     
Go to step 7.
     
NO
     
     
     
Go to step 13.
7.
A/C switch check:

A/C switch check
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Test the A/C switch.

Is the A/C switch OK?

     
YES
     
     
     
Go to step 8.
     
NO
     
     
     
A/C switch is faulty. Replace the heater control base.?
8.
Open wire check (A/C SW- line):

Open wire check (A/C SW- line)
?1.
Disconnect the following connector.
Heater fan switch 8P connector

?2.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
A/C switch 7P connector: disconnected
Heater fan switch 8P connector: disconnected
Test point 1
A/C switch 7P connector No. 5
Test point 2
Heater fan switch 8P connector No. 6


Is there continuity?

     
YES
     
     
     
The A/C SW- wire is OK. Go to step 9.
     
NO
     
     
     
Repair an open in the wire between the A/C switch and the heater fan switch.?
9.
Heater fan switch check:

Heater fan switch check
?1.
Test the heater fan switch.

Is the heater fan switch OK?

     
YES
     
     
     
Go to step 10.
     
NO
     
     
     
10.
Evaporator temperature sensor check:

Evaporator temperature sensor check
?1.
Test the evaporator temperature sensor.

Is the evaporator temperature sensor OK?

     
YES
     
     
     
Go to step 11.
     
NO
     
     
     
11.
Determine possible failure area (TEVA line, others):

Determine possible failure area (TEVA line, others)
?1.
Turn the vehicle to the ON mode.

?2.
Measure the voltage between test points 1 and 2.
Test condition
Vehicle ON mode
A/C switch 7P connector: disconnected
Heater fan switch 8P connector: disconnected
Evaporator temperature sensor 2P connector: disconnected
Test point 1
Evaporator temperature sensor 2P connector No. 2
Test point 2
Body ground


Is there about 5 V?

     
YES
     
     
     
The TEVA wire is not shorted. Go to step 12.
     
NO
     
     
     
Go to step 14.
12.
Open wire check (SG5 line):

Open wire check (SG5 line)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Jump the SCS line with the HDS.

NOTE: This step must be done to protect the PCM from damage.

?3.
Disconnect the following connector.
PCM connector A (51P)

?4.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
PCM connector A (51P): disconnected
A/C switch 7P connector: disconnected
Heater fan switch 8P connector: disconnected
Evaporator temperature sensor 2P connector: disconnected
Test point 1
PCM connector A (51P) No. 39
Test point 2
Evaporator temperature sensor 2P connector No. 1


Is there continuity?

     
YES
     
     
     
The SG5 wire is OK. Update the PCM if it does not have the latest software, or substitute a known-good PCM, then recheck. If the symptom/indication goes away with a known-good PCM, replace the original PCM.?
     
NO
     
     
     
Repair open in the wire between the PCM and the evaporator temperature sensor.?
13.
MICU check:

MICU check
?1.
Measure the voltage between test points 1 and 2.
Test condition
Vehicle ON mode
A/C switch 7P connector: disconnected
Test point 1
Under-dash fuse/relay box connector H (20P) No. 3
Test point 2
Body ground

Is there battery voltage?

     
YES
     
     
     
Repair an open in the wire between the under-dash fuse/relay box and the A/C switch.?
     
NO
     
     
     
14.
Open wire check (TEVA line):

Open wire check (TEVA line)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Jump the SCS line with the HDS.

NOTE: This step must be done to protect the PCM from damage.

?3.
Disconnect the following connector.
PCM connector A (51P)

?4.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
PCM connector A (51P): disconnected
A/C switch 7P connector: disconnected
Heater fan switch 8P connector: disconnected
Evaporator temperature sensor 2P connector: disconnected
Test point 1
PCM connector A (51P) No. 42
Test point 2
Evaporator temperature sensor 2P connector No. 2


Is there continuity?

     
YES
     
     
     
The TEVA wire is OK. Update the PCM if it does not have the latest software, or substitute a known-good PCM, then recheck. If the symptom/indication goes away with a known-good PCM, replace the original PCM.?
     
NO
     
     
     
Repair open in the wire between the PCM and the evaporator temperature sensor.?