GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Yukon - 4WD 🢒 HVAC 🢒 Heating, Ventilation, and Air Conditioning 🢒 Air Conditioning (A/C) Diagnostics - Pressure Zone B

Step

Action

Yes

No

DEFINITION: The low side pressure is higher than normal and the high side pressure is lower than normal.

    • Malfunctioning A/C Compressor
    • Refrigerant Under Charge

1

Were you sent here from the A/C System Performance Test?

Go to Step 2

Go to Air Conditioning (A/C) System Performance Test

2

After continued operation of the air conditioning (A/C) system, do the low and the high side pressures equalize or become static?

Go to Step 5

Go to Step 3

3

Refer to the pressures recorded during the A/C System Performance Test.

Inspect for the following conditions:

Caution: Refer to Moving Parts and Hot Surfaces Caution in the Preface section.

    • The low side pressure is equal to or greater than the specified pressure range of the A/C Performance Table. Refer to Air Conditioning (A/C) System Performance Test .
    • The high side pressure is less than the specified pressure range of the A/C Performance Table. Refer to Air Conditioning (A/C) System Performance Test .
    • The low side refrigerant line at the compressor feels cool-to-warm.
    • The high side refrigerant line at the compressor feels warm-to-hot.

Do the listed conditions exist?

Go to Step 5

Go to Step 4

4

Refer to the pressures recorded during the A/C System Performance Test.

Inspect for the following conditions:

Caution: Refer to Moving Parts and Hot Surfaces Caution in the Preface section.

    • The low side pressure is greater than the specified pressure range of the A/C Performance Table. Refer to Air Conditioning (A/C) System Performance Test .
    • The high side pressure is less than the specified pressure range of the A/C Performance Table. Refer to Air Conditioning (A/C) System Performance Test .
    • The low side refrigerant line at the compressor feels warm.
    • The high side refrigerant line at the compressor feels warm to hot.

Do the listed conditions exist ?

Go to Step 5

Go to Air Conditioning (A/C) System Performance Test

5

The A/C system has a low refrigerant charge.

Evacuate and recharge the A/C system. Refer to Refrigerant Recovery and Recharging .

Is the procedure complete?

Go to Step 6

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6
  1. Record the low and the high side pressures as well as the instrument panel (I/P) air outlet temperature after you perform the repairs.
  2. Compare the pressures and the panel outlet temperature to those listed in the A/C Performance Chart. Refer to Air Conditioning (A/C) System Performance Test .

Are the readings within the specified ranges found on the A/C Performance Chart?

Go to Step 13

Go to Step 7

7

The A/C compressor is malfunctioning.

Remove the expansion device and inspect for contamination. Refer to Expansion (Orifice) Tube Replacement .

Did you find metal flakes on the expansion device?

Go to Step 9

Go to Step 8

8

Inspect the expansion device for a brown, powdery residue indicating desiccant in the A/C system.

Is a brown, powdery residue present?

Go to Step 11

Go to Step 12

9
  1. Remove the suction and the discharge lines from the compressor. Refer to Suction Hose Replacement and to Discharge Hose Replacement .
  2. Inspect for metal flake contamination at the line connections and the compressor ports.

Is metal flake contamination present?

Go to Step 10

Go to Step 12

10
  1. Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement .
  2. Install an A/C refrigerant filter. Refer to Air Conditioning (AC) Refrigerant Filter Replacement .
  3. Replace the orifice tube. Refer to Expansion (Orifice) Tube Replacement .
  4. Evacuate and recharge the A/C system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

Go to Step 13

--

11
  1. Flush the A/C system. Refer to Flushing .
  2. Replace the orifice tube. Refer to Expansion (Orifice) Tube Replacement .
  3. Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement .
  4. Replace the accumulator. Refer to Air Conditioning Accumulator Replacement .
  5. Evacuate and recharge the A/C system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

Go to Step 13

--

12
  1. Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement .
  2. Evacuate and recharge the A/C system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

Go to Step 13

--

13

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Symptoms - HVAC Systems - Automatic