Opel Frontera UBS. Manual - part 287

6E–54

ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Control Circuit Diagnosis

D06RW085

Circuit Description

When air conditioning and blower fan are selected, and if
the system has a sufficient refrigerant charge,  a 12-volt
signal is supplied to the A/C request input of the
powertrain control module (PCM).  The A/C request
signal may be temporarily canceled during system
operation by the electronic thermostat in the evaporator
case.  The electronic thermostat may intermittently
remove the control circuit ground for the A/C thermostat
relay to prevent the evaporator from forming ice. When
the A/C request signal is received by the PCM, the PCM
supplies a ground from the compressor clutch relay if the
engine operating conditions are within acceptable
ranges.  With the A/C compressor relay energized,
voltage is supplied to the compressor clutch coil.
The PCM will enable the compressor clutch to engage
whenever A/C has been selected with the engine running,
unless any of the following conditions are present:

D

The throttle is greater than 90%.

D

The ignition voltage is below 10.5 volts.

D

The engine speed is greater than 4500 RPM for 5
seconds or 5400 RPM.

D

The engine coolant temperature (ECT) is greater than
125 

°

C (257 

°

F).

D

The intake air temperature (IAT) is less than 5

°

C

(41

°

F).

D

The power steering pressure switch signals a cramped
position.

Diagnostic Aids

To diagnose an the intermittent fault, check for the
following conditions:

D

Poor connection at the PCM–Inspect connections for
backed-out terminals, improper mating, broken locks,
improperly formed or damaged terminals, and poor
terminal-to-wire connection.

6E–55

ENGINE DRIVEABILITY AND EMISSIONS

D

Damaged harness–Inspect the wiring harness for
damage.  If the harness appears to OK, observe the
A/C clutch while moving connectors and wiring
harnesses related to the A/C.  A sudden clutch
malfunction will indicate the source of the intermittent
fault.

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.

9. The blower system furnishes a ground for the A/C

control circuit, and it also shares a power source
through the Heater and A/C Relay.  The blower
must be “ON” in order to test the A/C system.

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 45

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?

—

Refer to

Diagnostic

Aids

Go to 

Step 6

6E–56

ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Control Circuit Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

6

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

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

—

Go to 

Step 34

Go to 

Step 7

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

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

switch wire (BRN).

Was voltage equal to the specified value?

+B

Go to 

Step 15

Go to 

Step 14

14

Repair the open wire (BRN) between the A/C switch
and the A/C fuse.

Is the action complete?

—

Verify repair

—

15

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

PNK/GRN wire at the thermostat.

4. A/C “ON.”
5. Blower “ON.”

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

—

Go to 

Step 16

Go to 

Step 23

16

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 20

Go to 

Step 17

17

Check for an open (LT GRN) between the thermostat
and the A/C switch.

Was the wire open?

—

Go to 

Step 18

Go to 

Step 19

18

Repair the open wire (LT GRN) between the thermostat
and the A/C switch.

Is the action complete?

—

Verify repair

—

6E–57

ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Control Circuit Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

19

Replace the A/C switch.

Is the action complete?

—

Verify repair

—

20

Use an ohmmeter to check continuity between the
electronic A/C thermostat and the blower switch.

Was there an open circuit?

—

Go to 

Step 21

Go to 

Step 22

21

Repair the open wire (GRN/YEL) between the
thermostat and the blower switch.

Is the action complete?

—

Verify repair

—

22

Replace the electronic A/C thermostat.

Is the an action complete?

—

Verify repair

—

23

Check for an open circuit between A/C thermostat relay
and PCM A/C request terminal (E-15).

Was there an open circuit?

—

Go to 

Step 24

Go to 

Step 25

24

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

Is the action complete?

—

Verify repair

—

25

Check for an open circuit between the A/C switch (LT
GRN) and the A/C thermostat relay (LT GRN).

Was there an open circuit?

—

Go to 

Step 26

Go to 

Step 27

26

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

Is the action complete?

—

Verify repair

—

27

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

switch (BRN).

Was voltage equal to the specified value?

+B

Go to 

Step 29

Go to 

Step 28

28

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

Is the action complete?

—

Verify repair

—

29

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

Was the circuit open?

—

Go to 

Step 30

Go to 

Step 31

30

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

Is the action complete?

—

Verify repair

—

31

Check for damaged pin or terminal at E-15 of the PCM.

Was a damaged pin or terminal found?

—

Go to 

Step 32

Go to 

Step 33

32

Repair the damaged pin or terminal.

Is the action complete?

—

Verify repair

—

33

Replace the PCM.

IMPORTANT: The replacement PCM must be
programmed.  Refer to 

UBS 98model year Immobilizer

Workshop Manual.

Is the action complete?

—

Verify repair

—