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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 Savana 🢒 Body and Accessories 🢒 Wiring Systems 🢒 CCOT Air Conditioning (A/C) System Diagnosis

The Cycling Clutch Orifice Tube (CCOT) refrigerant system is used on this vehicle. The CCOT refrigeration system cycles a compressor on and off. The cycling maintains 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 A/C accumulator. 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 plugged.

If a low charge occurs, insufficient cooling accompanied by rapid compressor clutch cycling will be noticed at high ambient 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 Function Test?

--

Go to Step 2

Go to Function Test

2

Inspect the following components of the A/C system:

    • Blown or missing fuses
    • Loose or broken connectors
    • The blower fan operation

Did you find and repair a condition?

--

Go to Function Test

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. Turn the A/C 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 expansion (orifice) tube. Refer to Expansion (Orifice) Tube Replacement .
  3. Replace the compressor assembly. Refer to Air Conditioning Compressor Replacement .
  4. Evacuate and charge the system. Refer to Refrigerant Recovery and Recharging .
  5. Inspect the system for leaks. Refer to Leak Testing .

Are the repairs complete?

--

Go to Function Test

--

7

Replace the drive 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. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
  3. Repair the restriction.
  4. Evacuate the system. Refer to Refrigerant Recovery and Recharging .
  5. Charge the system.

Is the repair complete?

--

Go to Function Test

--

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. Refer to Leak Testing .
  2. If a leak is present recover the refrigerant.
  3. Evacuate and charge the system. Refer to Refrigerant Recovery and Recharging .

Did you find and repair a leak?

--

Go to Function Test

Go to Step 21

12
  1. Connect a fused jumper wire from the coil connector and jump both terminals.
  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 and charge the system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

--

Go to Function Test

--

16

Connect a fused jumper wire between the pressure switch and jump both terminals of the pressure switch connector.

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®. Refer to Leak Testing .

Is the repair complete?

--

Go to Function Test

--

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 Function Test

--

19

Apply an external ground to the compressor.

Does the compressor clutch engage?

--

Go to Function Test

Go to Step 20

20

Rebuild or Replace the compressor. Refer to Air Conditioning Compressor Replacement .

Is the repair complete?

--

Go to Function Test

--

21
  1. Add sufficient refrigerant to the system.
  2. Inspect the clutch cycle rate.

Is the clutch cycle rate greater than the specified value?

6 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 and charge the system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

--

Go to Function Test

--

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 Function Test

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 Function Test

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 System Performance Test. Refer to System Performance Test .

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

--

Go to Function Test

Go to Step 32

28

Does the compressor cycle 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. Refer to Expansion (Orifice) Tube Replacement .
  2. Evacuate and charge the system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

--

Go to Function Test

--

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 Function Test

--

37

Evacuate and charge the system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

--

Go to Function Test

--