Isuzu Trooper (1998-2002 year). Service 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
—
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