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

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Step Action Value Yes No
DEFINITION: The high and low side pressures may be normal or slightly less than normal.
  • Air Delivery Concern
  • Slight Refrigerant Under Charge
  • Refrigerant Contamination
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 (Diesel Engine)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/ Electric Cooling Fan)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/Engine Driven Fan) 
2 Refer to the panel air outlet temperatures recorded during the A/C system performance test.
Does the discharge air temperature between the right and left center panel outlets vary by more than 1-2°C (2-3°F)?		 - Go to Step 7  Go to Step 3 
3 Did the customer mention that the A/C system output temperatures are good at first, but then turn warm during extended drives? - Go to Step 4  Go to Step 5 
4 Increase engine speed to 2000 RPM.
During extended operation of the A/C system, does the low side pressure decrease, possibly accompanied by heavy frost on the liquid line between the expansion device and the evaporator?		 - Go to Air Conditioning (A/C) Diagnostics - Pressure Zone D  Go to Step 5 
5
  1. Refer to the pressures recorded during the A/C system performance test.
  2. Inspect for the following conditions:
Do the listed conditions exist?		 - Go to Step 7  Go to Step 6 
6
  1. Refer to the pressures recorded during the A/C system performance test.
  2. Inspect for the following conditions:
Do the listed conditions exist?		 - Go to Step 8  Go to Diagnostic Starting Point - Heating, Ventilation and Air Conditioning 
7 The A/C system may be undercharged.
  1. Leak test A/C system. Refer to Leak Testing .
  2. Recharge the A/C system to specifications. Refer to Refrigerant Recovery and Recharging .

Is the action complete?		 - Go to Step 14  -
8 The A/C system may be contaminated.
View the information screen on J 43600  ACS 2000 Air Conditioning Service Center for detection of foreign gases in the A/C system. See Special Tools .
Do foreign gases exist?		 - Go to Step 9  Go to Step 10 
9
  1. Evacuate the A/C system to a scavenging tank. Refer to Refrigerant Recovery and Recharging .
  2. Recharge the A/C system to specifications.
Is the action complete?		 - Go to Step 14  -
10 The A/C system may contain too much moisture or air.
  1. Evacuate and recharge the A/C system to specifications. Refer to Refrigerant Recovery and Recharging .
  2. Operate the A/C system and inspect the panel outlet air temperatures. Refer to Air Conditioning (A/C) System Performance Test (Diesel Engine)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/ Electric Cooling Fan)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/Engine Driven Fan) .

Are the panel outlet temperatures within the specified ranges of the A/C Performance Test Table?		 - Go to Step 15  Go to Step 11 
11 The A/C system may contain too much refrigerant oil.
  1. Recover the refrigerant from the A/C system. Refer to Refrigerant Recovery and Recharging .
  2. Remove the accumulator. Refer to Air Conditioning Accumulator Replacement (Non-HP2) .
  3. Drain and measure the refrigerant oil from the accumulator.

Was more than the specified amount of refrigerant oil drained from the accumulator?		 148 ml (5 oz) Go to Step 12  Go to Step 13 
12
  1. Reinstall the accumulator. Refer to Air Conditioning Accumulator Replacement (Non-HP2) .
  2. Flush the A/C system. Refer to Flushing .
  3. Recharge the A/C system. Refer to Refrigerant Recovery and Recharging .
Are the actions complete?		 - Go to Step 14  -
13
  1. Add the specified amount of refrigerant oil to the accumulator. Refer to Refrigerant System Capacities .
  2. Install the accumulator. Refer to Air Conditioning Accumulator Replacement (Non-HP2) .
  3. Recharge the A/C system. Refer to Refrigerant Recovery and Recharging .
Are the actions complete?		 - Go to Step 14  -
14
  1. Record the low and high side pressures and the I/P outlet air temperature.
  2. Compare the outlet temperatures to those listed in the A/C System Performance Chart. Refer to Air Conditioning (A/C) System Performance Test (Diesel Engine)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/ Electric Cooling Fan)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/Engine Driven Fan) .
Are the high and low side pressures and I/P panel outlet temperatures within specifications?		 - Go to Step 15  Go to Air Conditioning (A/C) System Performance Test (Diesel Engine)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/ Electric Cooling Fan)  or Air Conditioning (A/C) System Performance Test (Gas Engine w/Engine Driven Fan) 
15 Operate the system in order to verify the repair.
Did you find and correct the condition?		 - System OK Go to Symptoms - HVAC Systems - Manual
or
Go to Symptoms - HVAC Systems - Automatic
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