HVAC Compressor Clutch Does Not Engage. Chevrolet Silverado Classic

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2007 🢒 Silverado Classic - 2WD 🢒 Power and Signal Distribution 🢒 Wiring Systems and Power Management 🢒 HVAC Compressor Clutch Does Not Engage

Diagnostic Aids

A/C compressor clutch will not engage under the following conditions:

•	The A/C high side line pressure is over 2957 kPa (429 psi).

•	The A/C low side line pressure is under 138-172 kPa (20-25 psi).

•	Throttle angle is at 100 percent.

•	Engine speed is more than 5,500 RPM.

•	Engine coolant temperature (ECT) is more than 121°C (250°F).

•	Ambient air temperature is less than 5°C (40°F).

•	Engine is idling at a low unstable RPM

Compressor clutch engagement cannot be used to determine 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.

Test Description

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

The A/C compressor output is disabled if the engine is idling at a low unstable RPM.

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.

This step ensures that the HVAC control module is receiving an input from the A/C switch.

These actions will enable the A/C compressor to operate.

This test ensures that there is sufficient refrigerant in the A/C system. The specific values come from the A/C System Performance Test in Heating, Ventilation and Air Conditioning.

The A/C Low Pressure Switch parameter is out of range when the HVAC control module interprets the signal being below 138-172 kPa (20-25 psi).

This action will simulate a closed switch condition. If the Pressure Cycle Switch parameter reads Low Pressure than there is a circuit condition or a condition with the HVAC control module.

The A/C compressor relay output from the PCM is disabled if the A/C high side system pressure is interpreted to be higher than 2 958 kPa (429 psi).

Step

Action

Values

Yes

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

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

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

Start the engine.
Set the parking brake.
Place the vehicle in drive and allow the engine to idle.
Observe the engine RPM.

Does the engine idle at a steady RPM?

Go to Step 3

Go to

•	Rough, Unstable, or Incorrect Idle and Stalling for the 4.8L, 5.3L and 6.0L Engine

•	Rough, Unstable, or Incorrect Idle and Stalling for the 4.3L Engine

•	Rough, Unstable, or Incorrect Idle and Stalling for the 8.1L Engine

Start the engine.
Observe the coolant temperature indicator.

Is the engine coolant temperature indicator illuminated?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 4

Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the A/C Switch parameter in the Heating and Air Conditioning data list.
Activate the A/C request switch.

Does the scan tool indicate that the A/C Switch parameter changes states?

Go to Step 5

Go to Step 26

Important: For A/C compressor operation, the ambient air temperature must be above 5°C (40°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 left air temperature switch in the coldest position.

Does the A/C compressor clutch engage?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 6

Park the vehicle inside or out of direct sunlight.
Open the window in order to ventilate the interior of the vehicle.
Turn OFF the ignition.
If the A/C system was operating, then wait for approximately 2 minutes.
Install J 43600 ACR 2000 Air Conditioning Service Center.
Record the ambient temperature at the vehicle.
Record readings of the low and high side STATIC pressures.
Compare the low and the high side pressure values with the allowable limits for the recorded ambient air temperature.

Are the low and the high side pressure values within the allowable limits for the recorded ambient air temperature. Are the pressure values within 103 kPa (15 psi) of each other?

Above 16°C (60°F) 345 kPa (50 psi)

Above 24°C (75°F) 483 kPa (70 psi)

Above 33°C (90°F) 690 kPa (100 psi)

Go to Step 7

Go to Leak Testing

Start the engine.
With a scan tool, observe the A/C Permission parameter in the Heating and Air Conditioning data list.

Does the A/C Permission parameter display Granted?

Go to Step 14

Go to Step 8

Turn OFF the ignition.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the Pressure Cycle Switch parameter in the Heating and Air Conditioning data list.

Does the Pressure Cycle Switch parameter display Normal?

Go to Step 12

Go to Step 9

Turn OFF the ignition.
Disconnect the A/C low pressure switch.
Turn ON the ignition, with the engine OFF.
Connect a 3-ampere fused jumper between the signal circuit and the ground circuit of the A/C low pressure switch.
Observe the Pressure Cycle Switch parameter in the Heating and Air Conditioning data list.

Does the Pressure Cycle Switch parameter display Normal?

Go to Step 23

Go to Step 10

Test the signal circuit of the A/C low pressure switch for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?