GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2000 🢒 S/T Isuzu - 2WD 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 CCOT Air Conditioning (A/C) System Diagnosis

The Cycling Clutch Orifice Tube (CCOT) refrigerant system is used on vehicles that are equipped with 4.3L engines. The CCOT refrigeration system cycles a compressor ON and OFF. The cycles maintain desired cooling and prevent evaporator freeze-up. Passenger compartment comfort is maintained by selecting the following on the control assembly:

    • The mode
    • The fan speed
    • The air temperature

The refrigeration cycle is controlled by a switch that senses low-side pressure as an indicator of evaporator pressure. The switch is the freeze protection device in the system that senses refrigerant pressure on the suction side of the system. The switch is located on the low-side service fitting, which is standard for this system. The equalized pressures within the charged air conditioning system close the contacts of the pressure switch when the air temperature is between 16°-26°C (60°-80°F).

Voltage is supplied to the compressor coil switch when an air conditioning mode is selected. The compressor reduces the evaporator pressure to approximately 175 kPa (25 psi). The pressure switch then opens, which de-energizes the compressor clutch. As the pressure system equalizes and the pressure reaches approximately 315 kPa (46 psi), the pressure switch contacts close. This re-energizes the clutch coil.

Under certain conditions, cycling may cause increases and decreases of engine speed. This is a normal condition. The system is designed to maintain desired cooling, which prevents evaporator freeze-up.

The operating characteristics of the low-side pressure cycling switch provides additional compressor protection. Low-side pressures could be insufficient to close the contacts of the pressure switch under the following conditions:

    • A massive discharge occurs in the low side of the system
    • The orifice tube becomes unplugged

If a low charge occurs, insufficient cooling accompanied by rapid compressor clutch cycling will be noticed at high air temperatures.

When the engine is turned OFF while the air conditioning system is operating, the refrigerant in the system will continue to flow. The refrigerant will flow from the high-pressure side of expansion tube (orifice) to the low pressure side until the pressure is equalized. The equalization can be detected as a hissing sound for 30-60 seconds. This is a normal condition.

Step

Action

Value(s)

Yes

No

1

Inspect the following components of the A/C system:

    • The fuses
    • The wire connectors
    • The blower fan operation

Did you find and repair a condition?

--

System OK

Go to Step 2

2

Inspect the drive belt.

Does the drive belt operate properly?

--

Go to Step 3

Go to Step 4

3

Important: The ambient temperature must be above 10°C (50°F) for completion of this diagnostic procedure.

Inspect the compressor clutch engagement by following these steps:

  1. Start the engine.

    2. Idle the engine.

  2. Push the A/C push-button to the ON position.
  3. Turn the mode control knob to the UPPER position.
  4. Turn the blower knob to the MAX position.
  5. Observe the clutch operation for a period of 5 minutes.

Does the clutch engage or cycle?

--

Go to Step 7

Go to Step 11

4

Has the compressor seized?

--

Go to Step 5

Go to Step 6

5
  1. Replace the compressor assembly. Refer to Air Conditioning Compressor Replacement .
  2. Replace the orifice.
  3. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  4. Evacuate the system.
  5. Charge the system.
  6. Inspect the system for leaks.

Are the repairs complete?

--

System OK

--

6

Tighten or replace the belt, as necessary.

Is the repair complete?

--

Go to Step 3

--

7

Feel the liquid line before the orifice tube.

Is the liquid line cold?

--

Go to Step 8

Go to Step 9

8
  1. Inspect the high side of the system for a frost spot in order to locate a restriction.
  2. Repair the restriction.
  3. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  4. Evacuate the system.
  5. Charge the system.

Is the repair complete?

--

System OK

--

9
  1. Feel the evaporator inlet pipe.
  2. Feel the evaporator outlet pipe.

Is the inlet pipe colder than the outlet pipe?

--

Go to Step 10

Go to Step 24

10
  1. Conduct a leak test of the system.
  2. Repair any leaks, as necessary.
    3. 2.1. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
    2.2. Evacuate the system.
    2.3. Charge the system.

Did you find and repair a leak?

--

System OK

Go to Step 20

11
  1. Connect a fused jumper wire from the compressor hot lead to the positive battery post.
  2. Observe the compressor operation.

Does the compressor clutch engage?

--

Go to Step 12

Go to Step 18

12
  1. Remove the jumper.
  2. Inspect the refrigerant pressure at the accumulator fitting.

Is the pressure below the specified value?

345 kPa (50 psi)

Go to Step 13

Go to Step 15

13

Inspect the refrigerant pressure on the high side of the system.

Is the pressure above the specified value?

345 kPa (50 psi)

Go to Step 14

Go to Step 10

14
  1. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  2. Inspect for the following conditions:
    3. 2.1. A plugged orifice
    2.2. A restriction in the high side of the system
  3. Complete the necessary repairs, or replace the orifice.
  4. Evacuate the system.
  5. Charge the system.

Is the repair complete?

--

System OK

--

15

Connect a fused jumper wire between the pressure switch and the positive battery post.

Does the compressor operate?

--

Go to Step 16

Go to Step 17

16
  1. Replace the pressure switch.

    2. Important: Do not recover the refrigerant.

  2. Conduct a leak test at the Schrader Valve®.

Is the repair complete?

--

System OK

--

17
  1. Inspect the pressure switch for an open circuit or a broken wire.
  2. Complete any necessary repairs.

Is the repair complete?

--

System OK

--

18

Apply an external ground to the compressor.

Does the compressor clutch engage?

--

System OK

Go to Step 19

19

Rebuild the compressor.

Is the repair complete?

--

System OK

--

20
  1. Add 0.45 kg (1 lb) of refrigerant to the system.
  2. Inspect the clutch cycle rate.

Is the clutch cycle rate greater than the specified value?

8 cycles/minute

Go to Step 21

Go to Step 22

21
  1. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  2. Inspect for a plugged orifice.
  3. Repair the orifice as necessary.
  4. Evacuate the system.
  5. Charge the system.

Is the repair complete?

--

System OK

--

22
  1. Feel the evaporator inlet pipe.
  2. Feel the evaporator outlet pipe.

Is the inlet pipe colder than the outlet pipe?

--

Go to Step 23

System OK

23
  1. Add 0.45 kg (1 lb) of refrigerant to the system.
  2. Feel the evaporator inlet pipe.
  3. Feel the evaporator outlet pipe.

Is the inlet pipe colder than the outlet pipe?

--

Go to Step 21

System OK

24
  1. Install a gauge set.
  2. Inspect the compressor cycling pressure.

Does the compressor cycle on within the specified value range?

280-350 kPa (41-51 psi)

Go to Step 25

Go to Step 27

25

Does the compressor cycle off within the specified value range?

140-190 kPa (20-28 psi)

Go to Step 26

Go to Step 27

26
  1. Push the A/C push-button to the ON position.
  2. Turn the mode control knob to the upper vents position.
  3. Turn the blower knob to the HI position.
  4. Close the doors and windows of the vehicle.
  5. Stabilize the engine speed for 5 minutes.
  6. Install a thermometer in the A/C outlet.
  7. Perform the Performance Test. Refer to System Performance Test .

Is the temperature performance within the limits of the test specifications?

--

System OK

Go to Step 31

27

Does the compressor cycle high ON above the specified value?

350 kPa (51 psi)

Go to Step 28

Go to Step 29

28

Does the compressor cycle OFF below the specified value?

140 kPa (20 psi)

Go to Step 16

Go to

29
  1. Disconnect the blower wire.
  2. Determine when the compressor cycles OFF.

Does the compressor cycle OFF below the specified value range?

140 kPa (20 psi)

Go to Step 16

Go to Step 30

30

Reconnect the blower motor wire.

Is the wire reconnected?

--

Go to Step 26

--

31

Observe the compressor cycling.

Does the compressor cycle on continuously?

--

Go to Step 32

Go to Step 21

32
  1. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  2. Inspect the orifice.

Is the orifice missing?

--

Go to Step 33

Go to Step 34

33
  1. Install the orifice.
  2. Evacuate the system.
  3. Charge the system.

Is the repair complete?

--

System OK

--

34

Inspect the suction line.

Is the suction line restricted?

--

Go to Step 35

Go to Step 36

35

Repair the suction line, as required.

Is the repair complete?

--

System OK

--

36
  1. Evacuate the system
  2. Charge the system

Is the repair complete?

--

System OK

--