GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2009 🢒 XLR 🢒 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 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:

Warning: Refer to Moving Parts and Hot Surfaces Warning 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:

Warning: Refer to Moving Parts and Hot Surfaces Warning 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 Step 6

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 11

--

6

The A/C compressor is malfunctioning.

Remove the refrigerant filter and inspect for contamination. Refer to Air Conditioning (AC) Refrigerant Filter Replacement.

Did you find metal flakes on the refrigerant filter?

Go to Step 8

Go to Step 7

7

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

Is a brown, powdery residue present?

Go to Step 9

Go to Step 10

8
  1. Replace the refrigerant filter. Refer to Air Conditioning (AC) Refrigerant Filter Replacement.
  2. Evacuate and recharge the A/C system. Refer to Refrigerant Recovery and Recharging.

Is the repair complete?

Go to Step 11

--

9
  1. Flush the A/C system. Refer to Flushing.
  2. Replace the thermal expansion valve. Refer to Air Conditioning Evaporator Thermal Expansion Valve Replacement.
  3. Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement.
  4. Replace the condenser. Refer to Air Conditioning Condenser Replacement.
  5. Evacuate and recharge the A/C system. Refer to Refrigerant Recovery and Recharging.

Is the repair complete?

Go to Step 11

--

10
  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 11

--

11

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Symptoms - HVAC Systems - Automatic