HVAC Compressor Clutch Does Not Engage. GMC Truck GMC C Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 HVAC Compressor Clutch Does Not Engage

Test Description

The numbers below refer to the step numbers on the diagnostic table.

The A/C compressor relay output is disabled if engine coolant temperature is above 121°C (250°F). The engine coolant indicator will illuminate at this temperature.

The HVAC control module is inoperative when the module does not respond to any operator control requests.

When the blower motor is in the OFF position, a voltage is applied to the OFF blower motor control circuit. The A/C system will not operate if a voltage is applied to the OFF blower motor control circuit.

Step

Action

Yes

Schematic Reference: HVAC Schematics

DEFINITION: A/C compressor clutch will not engage when an A/C request has been made and a Powertrain DTC has not been set.

Important:

•

Compressor clutch engagement cannot be used to determine the status of the low pressure switch. The low pressure switch is one of several inputs to the HVAC control module for A/C request authorization. A/C request is one of several inputs to the powertrain control module (PCM) that control A/C compressor clutch engagement.

•	To accurately determine what pressure the A/C low pressure switch opens and closes at use Kent Moore GE-47742 which will allow the technician to measure the switch point pressure at the switch.

•	Using a scan tool, monitor the "low pressure switch" status while monitoring the "low side" pressure at the switch to determine the switch points of the low pressure switch.

•

The low pressure switch "connector seal" must be removed before plugging it into the switch for testing. The "plunger effect" of plugging the connector with seal into the switch induces a pressure on the back side of the switch, this pressure will skew the opening/closing characteristics of the switch 5-10 psi until the pressure bleeds off. The time required for the connection induced pressure to bleed off can take 20 minutes or longer.

Did you review the HVAC operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

Start the engine.
Observe the coolant temperature indicator.

Is the engine coolant temperature indicator illuminated?

Go to Engine Coolant Temperature Indicator Always On in Engine Cooling

Go to Step 3

Important: For A/C compressor operation, ambient air temperature must be above 3°C (38°F).

Start the engine.
Place the blower motor switch in the maximum speed position.
Place the A/C request switch in the ON position.
Place the air temperature switch in the coldest position.

Does the A/C compressor operate?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 4

Park the vehicle inside or in the shade.
Open the windows in order to ventilate the interior of the vehicle.
If the A/C system was operating, then allow the A/C system to equalize for approximately 2 minutes.
Ensure that the ignition key is in the OFF position.
Install the J 43600 ACR 2000.
Record the ambient temperature at the vehicle.
Record readings of the low and high side STATIC pressures.
Compare the pressure values with the specifications for the ambient air temperature. Refer to Air Conditioning (A/C) System Performance Test in Heating, Ventilation and Air Conditioning.

Are the pressure values within the specifications for the ambient air temperature, and within 103 kPa (15 psi) of each other?

Go to Step 5

Go to Leak Testing in Heating, Ventilation and Air Conditioning

Is the HVAC control module inoperative?

Go to Step 20

Go to Step 6

Start the engine.
With a scan tool, observe the A/C Request Signal parameter.
Place the A/C request switch in the ON position.

Does the scan tool indicate that the A/C Request Signal parameter is YES?

Go to Step 9

Go to Step 7

Does the A/C request indicator illuminate?

Go to Step 8

Go to Step 22

Important: Ensure that the blower motor switch is not in the OFF position during this step.

Turn OFF the ignition.
Disconnect the A/C high pressure switch.
Connect a 3-amp fused jumper wire between the A/C request circuits at the A/C high pressure switch connector.
Start the engine.
With a scan tool, observe the A/C Request Signal parameter.
Place the A/C request switch in the ON position.

Does the scan tool indicate that the A/C Request Signal parameter is YES?

Go to Step 33

Go to Step 27

Does the scan tool indicate the A/C Compressor Cycling Switch parameter is closed?

Go to Step 11

Go to Step 10

Turn OFF the ignition.
Disconnect the A/C low pressure switch.
Connect a 3-amp fused jumper wire between the A/C low pressure switch signal and ground circuits.
Start the engine.
With a scan tool, observe the A/C Compressor Cycling Switch parameter.

Does the scan tool indicate the A/C Compressor Cycling Switch parameter is normal?

Go to Step 30

Go to Step 23

With a scan tool, command the A/C compressor clutch relay ON and OFF.

Does the A/C compressor clutch relay turn ON and OFF with each command?

Go to Step 17

Go to Step 12

Turn OFF the ignition.
Disconnect the A/C compressor clutch relay.
Turn ON the ignition, with the engine OFF.
Probe the coil side voltage supply circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 13

Go to Step 28

Connect a test lamp between the control circuit of the A/C compressor clutch relay and the coil side voltage supply circuit of the A/C compressor clutch relay.
With a scan tool, command the A/C compressor clutch relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 29

Go to Step 14

Does the test lamp remain illuminated with each command?

Go to Step 16

Go to Step 15

Test the control circuit of the A/C compressor clutch relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?