GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 Jimmy - 2WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 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 prevents 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 in order 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

Did you perform the Functional Check?

--

Go to Step 2

Go to Functional Check

2

Inspect the following components of the A/C system:

    • The fuses
    • The hood rear seal
    • The wire connectors
    • The blower fan operation

Did you find and repair a condition?

--

Go to Functional Check

Go to Step 3

3

Inspect the drive belt.

Does the drive belt operate properly?

--

Go to Step 4

Go to Step 5

4

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 8

Go to Step 12

5

Has the compressor seized?

--

Go to Step 6

Go to Step 7

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

Are the repairs complete?

--

Go to Functional Check

--

7

Replace the belt.

Is the repair complete?

--

Go to Step 4

--

8

Feel the liquid line before the orifice tube.

Is the liquid line cold?

--

Go to Step 9

Go to Step 10

9
  1. Inspect the high side of the system for a frost spot in order to locate a restriction.
  2. Charge the system.
  3. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  4. Evacuate the system.
  5. Repair the restriction.

Is the repair complete?

--

Go to Functional Check

--

10
  1. Feel the evaporator inlet pipe.
  2. Feel the evaporator outlet pipe.

Is the inlet pipe slightly colder than the outlet pipe?

--

Go to Step 11

Go to Step 25

11
  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?

--

Go to Functional Check

Go to Step 21

12
  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 13

Go to Step 19

13
  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 14

Go to Step 16

14

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 15

Go to Step 11

15
  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?

--

Go to Functional Check

--

16

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

Does the compressor operate?

--

Go to Step 17

Go to Step 18

17
  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?

--

Go to Functional Check

--

18
  1. Inspect the pressure switch for an open circuit or a broken wire.
  2. Complete any necessary repairs.

Is the repair complete?

--

Go to Functional Check

--

19

Apply an external ground to the compressor.

Does the compressor clutch engage?

--

Go to Functional Check

Go to Step 20

20

Rebuild the compressor.

Is the repair complete?

--

Go to Functional Check

--

21
  1. Add sufficient 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 22

Go to Step 23

22
  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?

--

Go to Functional Check

--

23
  1. Feel the evaporator inlet pipe.
  2. Feel the evaporator outlet pipe.

Is the inlet pipe colder than the outlet pipe?

--

Go to Step 24

Go to Functional Check

24
  1. Leak test the system. Perform any repairs as necessary.
  2. Add sufficient refrigerant to the system.
  3. Feel the evaporator inlet pipe.
  4. Feel the evaporator outlet pipe.

Is the inlet pipe warmer than the outlet pipe?

--

Go to Step 22

Go to Functional Check

25
  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 26

Go to Step 28

26

Does the compressor cycle off within the specified value range?

140-190 kPa (20-28 psi)

Go to Step 27

Go to Step 28

27
  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?

--

Go to Functional Check

Go to Step 32

28

Does the compressor cycle high on above the specified value?

350 kPa (51 psi)

Go to Step 29

Go to Step 30

29

Does the compressor cycle OFF below the specified value?

140 kPa (20 psi)

Go to Step 17

Go to Step 32

30
  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 17

Go to Step 31

31

Reconnect the blower motor wire.

Is the wire reconnected?

--

Go to Step 27

--

32

Observe the compressor cycling.

Does the compressor cycle on continuously?

--

Go to Step 33

Go to Step 22

33
  1. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  2. Inspect the orifice tube for restrictions or missing seals.

Is the orifice missing?

--

Go to Step 34

Go to Step 35

34
  1. Install the orifice.
  2. Evacuate the system.
  3. Charge the system.

Is the repair complete?

--

Go to Functional Check

--

35

Inspect the suction line.

Is the suction line restricted?

--

Go to Step 36

Go to Step 37

36

Repair the suction line, as required.

Is the repair complete?

--

Go to Functional Check

--

37
  1. Evacuate the system.
  2. Charge the system.

Is the repair complete?

--

Go to Functional Check

--