GMC TRUCK A/C RANDOMLY STOPS WORKING DIAGNOSIS & FIX

Introduction

This tutorial provides a step-by-step guide to diagnosing and fixing an intermittent air conditioning (A/C) issue in a 2005 GMC Sierra with a 5.3L V8 engine. If your A/C randomly stops blowing cold air, this guide will help you identify the problem and understand how to address it effectively.

Step 1: Initial Assessment

• Start the vehicle and let it idle for about 15 minutes to check if the A/C is functioning.
• Observe the temperature of the air blowing from the A/C vents.
• If the A/C is blowing cold air, you will need to take the vehicle for a test drive to replicate the issue.

Step 2: Monitor A/C System Data

• Connect a scan tool to the vehicle’s OBD-II port.
• Monitor the following data pins while driving:
  • A/C Pressure Switch: Should read around 200 psi when the A/C is engaged.
  • A/C Relay Command: Should indicate that the relay is on.
  • A/C Request Signal: Should show "yes" when the A/C button is pressed.

Step 3: Conduct a Test Drive

• Drive the vehicle and pay attention to changes in A/C performance.
• If the A/C stops blowing cold air, check the scan tool readings again.
• Note any changes in the A/C pressure and relay command.

Step 4: Visual Inspection of A/C Compressor

• Once back at the garage, pop the hood and visually inspect the A/C compressor.
• Check if the clutch is engaged. If it is not engaged, the compressor may not be functioning properly.

Step 5: Check for Power at the Compressor Clutch

• Use a multimeter to test the power and ground at the compressor clutch connector:

  • Back probe both pins of the connector.
  • Set up your meter to monitor voltage and ground while driving.

• Look for the following readings:

  • Power Feed: Should be around 12-14 volts.
  • Ground: Should have minimal millivolts, indicating a solid ground connection.

Step 6: Analyze Readings

• After the A/C stops blowing cold air again, check the meter readings:
  • If you have good voltage and ground but the clutch is not engaging, the A/C compressor clutch is likely faulty.

Step 7: Replace the A/C Compressor (if needed)

• If diagnostics confirm a faulty clutch, prepare to replace the compressor:

  • Raise the vehicle and remove the front wheel to access the compressor via the wheel well.
  • Remove the serpentine belt and any necessary components to access the compressor.
  • Replace the compressor, dryer, and orifice tube as a kit, which often includes a warranty.

• Ensure to evacuate the A/C system properly before disconnecting lines, using a recovery service if you lack a recovery machine.

Conclusion

Diagnosing an intermittent A/C issue involves monitoring system data, checking the compressor, and verifying power and ground at the clutch. If a faulty compressor is confirmed, replacement is necessary. By following these steps, you can efficiently troubleshoot and resolve A/C problems in your GMC Sierra. Always remember to prioritize safety and consult a professional if you're unsure about any steps in the repair process.