Isuzu Trooper (1998-2002 year). Manual - part 424

6E–66

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Diagnosis

This chart should be used for diagnosing the electrical
portion of the A/C compressor clutch circuit.  A Tech 2 will
be used in diagnosing the system.  The Tech 2 has the
ability to read the A/C request input to the PCM.  The
Tech 2 can display when the PCM has commanded the
A/C clutch “ON”.  The Tech 2 should have the ability to
override the A/C request signal and energize the A/C
compressor relay.

Test Description

IMPORTANT:

Do not engage the A/C compressor

clutch with the engine running if an A/C mode is not
selected at the A/C control switch.
The numbers below refer to the step numbers on the
Diagnostic Chart:

3. This a test determine is the problem is with the

refrigerant system.  If the switch is open, A/C
pressure gauges will be used to determine if the
pressure switch is faulty or if the system is partially
discharged or empty.

4. Although the normal complaint will be the A/C clutch

failing to engage, it is possible for a short circuit to
cause the clutch to run when A/C has not been
selected.  This step is a test for that condition.

7. There is an extremely low probability that both relays

will fail at the same time, so the substitution process
is one way to check the A/C Thermostat relay.  Use
a known good relay to do a substitution check.

A/C Clutch Control Circuit Diagnosis

 

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to 

Step 2

Go to 

OBD

System

Check

2

Are any other DTCs stored?

—

Go to the

other DTC

chart(s) first

Go to 

Step 3

3

1. Disconnect the electrical connector at the pressure

switch located on the receiver/drier.

2. Use an ohmmeter to check continuity across the

pressure switch.

Is the pressure switch open?

—

Go to Air

Conditioning

to diagnose

the cause of

the open
pressure

switch

Go to 

Step 4

4

IMPORTANT: Before continuing with the diagnosis, the
following conditions must be met:

D

The intake air temperature must be greater than
15

°

C. (60

°

F).

D

The engine coolant temperature must be less
than 119

°

C (246

°

F).

1. A/C “OFF”.
2. Start the engine and idle for 1 minute.
3. Observe the A/C compressor.

Is the A/C compressor clutch engaged even though
A/C has not been requested?

—

Go to 

Step 37

Go to 

Step 5

5

1. Idle the engine.
2. A/C “ON”.
3. Blower “ON”.
4. Observe the A/C compressor.

Is the A/C compressor magnetic clutch engaged?

—

Check the

Procedure

Refer to

Diagnostic

Aids

Go to 

Step 6

6

1. Engine idling.
2. A/C “ON”.
3. Blower “ON”.
4. Observe the “A/C Request” display on the Tech 2.

(Refer to the Miscellaneous test)

Does the tool “A/C Request” display indicate “Yes”?

—

Go to 

Step 26

Go to 

Step 7

6E–67

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Control Circuit Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

7

Temporarily substitute the A/C compressor relay in
place of the A/C thermostat relay, then repeat Step 5.

Did the “A/C Request” display indicate “Yes”?

—

Go to 

Step 8

Go to 

Step 9

8

Replace the original A/C thermostat relay.

Is the action complete?

—

Verify repair

—

9

Does the blower operate?

—

Go to 

Step 10

Go to 

Step 11

10

Repair the blower.

Is the action complete?

—

Verify repair

—

11

Check for a faulty 10A A/C fuse in the underdash fuse
panel.

Was the 10A fuse OK?

—

Go to 

Step 13

Go to 

Step 12

12

Check for short circuit and make repairs if necessary.
Replace the 10A A/C fuse.

Is the action complete?

—

Verify repair

—

13

1. Remove the glove box to gain access to the A/C

thermostat.

2. Disconnect the thermostat connector.
3. Attach a fused jumper between ground and the

thermostat wire.

4. A/C “ON”.
5. Blower “ON”.

Dose A/C request indicate “YES” on the Tech 2?

—

Go to 

Step 14

Go to 

Step 17

14

1. Ignition “ON”.
2. Use a DVM to check voltage at the electronic A/C

thermostat.

Was voltage equal to the specified value?

B+

Go to 

Step 17

Go to 

Step 15

15

Check for open wire between the thermostat and the
A/C switch.

Was the wire open?

—

Go to 

Step 16

Go to 

Step 17

16

Repair the open wire between the thermostat and the
A/C switch.

Is the action complete?

—

Verify repair

—

17

Check for an open circuit between A/C thermostat relay
and PCM A/C request terminal (F45).

Was there an open circuit?

—

Go to 

Step 18

Go to 

Step 19

18

Repair the open circuit between the PCM and A/C
thermostat relay.

Is the action complete?

—

Verify repair

—

19

1. Ignition “ON”.
2. Use a DVM to check voltage at the A/C pressure

switch.

Was voltage equal to the specified value?

B+

Go to 

Step 21

Go to 

Step 20

20

Repair the open circuit between the 10A A/C fuse and
the pressure switch.

Is the action complete?

—

Verify repair

—

6E–68

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Control Circuit Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

21

Use an ohmmeter to check continuity between the
pressure switch and the A/C thermostat relay.

Was the circuit open?

—

Go to 

Step 22

Go to 

Step 23

22

Repair the open circuit between the pressure switch
and the A/C thermostat relay.

Is the action complete?

—

Verify repair

—

23

Check for damaged pin or terminal at F45 of the PCM.

Was a damaged pin or terminal found?

—

Go to 

Step 24

Go to 

Step 25

24

Repair the damaged pin or terminal.

Is the action complete?

—

Verify repair

—

25

Replace the PCM.

IMPORTANT: The replacement PCM must be
programmed.  Refer to 

On-Vehicle Service in

Powertrain Control Module Sensors for procedures.

And also refer to latest Service Bulletin.

Check to see if the Latest software is released or not.
And then Down Load the LATEST PROGRAMMED
SOFTWARE to the replacement PCM.

Is the action complete?

—

Verify repair

—

26

1. Remove the A/C compressor relay.
2. Ignition “ON”.
3. Use a DVM to check voltage at both of the wires at

the A/C compressor relay socket.

Is the voltage equal to the specified value?

B+

Go to 

Step 28

Go to 

Step 27

27

Repair the faulty wire between the A/C fuse and the
A/C compressor relay .

Is the action complete?

—

Verify repair

—

28

1. A/C compressor relay removed.
2. Engine idling.
3. A/C “ON”.
4. Blower “ON”.
5. Use a DVM to measure voltage between the wire at

the A/C compressor relay socket and battery

±

.

Did the DVM indicate the specified value?

B+

Go to 

Step 32

Go to 

Step 29

29

Check for an open wire between PCM terminal F4 and
the A/C compressor relay.

Was the wire open?

—

Go to 

Step 30

Go to 

Step 31

30

Repair the open wire between the PCM and the A/C
compressor relay.

Is the action complete?

—

Verify repair

—

31

Check for a damaged pin or terminal at F4 of the PCM.

Was a damaged pin or a terminal found?

—

Go to 

Step 24

Go to 

Step 25

6E–69

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Control Circuit Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

32

1. A/C compressor relay removed.
2. Connect a fused jumper at the A/C compressor

relay socket with either wire.

3. Engine idling.
4. A/C “ON”.
5. Blower “ON”.

Did the compressor magnetic clutch engage?

—

Go to 

Step 33

Go to 

Step 34

33

Repair the A/C compressor relay.

Is the action complete?

—

Verify repair

—

34

Check for an open circuit between the A/C compressor
relay and the A/C clutch.

Was an open circuit found?

—

Go to 

Step 35

Go to 

Step 36

35

Repair the open circuit between the compressor Clutch
and the A/C compressor relay.

Is the action complete?

—

Verify repair

—

36

Service the compressor clutch or replace the
compressor due to a faulty internal overheat switch.

Is the action complete?

—

Verify repair

—

37

1. Remove the A/C compressor relay.
2. Idle the engine.

Is the compressor clutch still engaged when A/C is not
selected?

—

Go to 

Step 38

Go to 

Step 39

38

Repair the short to voltage between the A/C clutch and
A/C compressor relay.

Is the action complete?

—

Verify repair

—

39

1. Reinstall the A/C compressor relay.
2. Remove the A/C thermostat relay.
3. Engine idling.

Is the compressor clutch still engaged when A/C is not
selected?

—

Go to 

Step 40

Go to 

Step 42

40

Use a DVM to check for a short to ground between the
A/C compressor relay and F4 of the PCM.

Was a short detected?

—

Go to 

Step 41

Go to 

Step 25

41

Repair the short to ground between the PCM and A/C
compressor relay.

Is the action complete?

—

Verify repair

—

42

Repair the short to ground between the A/C thermostat
relay and the electronic thermostat.

Is the action complete?

—

Verify repair

—