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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1098 (Heating, Ventilation, And Air Conditioning) >> Diagnostic Information and Procedures >> Air Conditioning (A/C) Diagnostics - Pressure Zone B

Air Conditioning (A/C) Diagnostics - Pressure Zone B

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
Step Action Value 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 Refer to the pressures recorded during the A/C System Performance Test.
Inspect for the following conditions:
Do the listed conditions exist?		 - Go to Step   3  Go to Step 7 
3 The A/C system may be undercharged or have compressor or expansion valve problems.
  1. Leak test the A/C system. Refer to Leak Testing .
  2. Note any potential leaks for later repair.
  3. Recover the refrigerant charge from the vehicle. Refer to Refrigerant Recovery and Recharging .
  4. Record the weight of the recovered refrigerant.

Is the recovered amount below the specified values?		 Standard A/C 0.625 kg (1.38 lbs) Go to Step 4  Go to Step 6 
4 The system is low on refrigerant charge.
  1. Repair any leaks noted in step 3 above.
  2. Evacuate and Recharge the A/C system to specifications. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?		 - Go to Step 5  -
5
  1. Record the low and the high side pressures and the instrument panel (I/P) outlet temperatures. Refer to step 2 of the Air Conditioning (A/C) System Performance Test.
  2. Compare the panel outlet temperatures and pressures to those listed in the A/C System Performance Chart.
Are the high and low side pressures and I/P outlet temperatures within specification?		 - System OK Go to Air Conditioning (A/C) System Performance Test 
6 The thermal expansion valve needs to be replaced.
  1. Replace the thermal expansion valve. Refer to Thermal Expansion Valve Replacement .
  2. Repair any leaks noted in step 3 above.
  3. Evacuate and recharge the A/C system to specifications. Refer to Refrigerant Recovery and Recharging .


Is the repair complete?		 - Go to Step 5  -
7 Refer to the pressures recorded during the A/C System Performance Test.
Inspect for the following conditions:
Do the listed conditions exist?		 - Go to Step 8  Go to Air Conditioning (A/C) System Performance Test 
8 The system could be low charged or there could be a problem with the A/C compressor.
  1. Verify that the compressor is engaging properly.
  2. Verify that the A/C system performance data was taken with the compressor clutch engaged for more than 10 seconds.
  3. Raise the engine RPM to 1,200.
  4. Record the low and high side pressures and the I/P panel outlet temperatures. Refer to step  2 of the Air Conditioning (A/C) System Performance Test.
  5. Compare the panel outlet temperatures and pressures to those listed in the A/C System Performance Chart.

Are the high and low side pressures and I/P panel outlet temperatures within specification?		 - Go to Step 3  Go to Step 9 
9 With the engine speed raised to over 2,000 RPM and the A/C compressor clutch engaged, listen for any unusual compressor noises.
Any unusual noises heard?		 - Go to Step 3  Go to Step 10 
10
  1. Replace the A/C compressor. Refer to 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
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