Tech Tip: What to do when A/C blows hot air

Oct. 19, 2021

Technician was advised the A/C system uses a compressor with a variable solenoid to control compressor engagement instead of a traditional clutch.

Richard Diegle

Vehicle: 2008 Volkswagen R32 4Motion (1K1), V6-3.2L (CBRA), Automatic Transmission/Transaxle

Mileage: 135,750

Problem: The owner of this R32 complained that the A/C was "not blowing cold air." It was an automatic HVAC system. The compressor appeared to be engaged.

Case Details: The technician scanned for diagnostic trouble codes (DTCs) and found:

DTC 00819 - High Pressure Sensor (G65) Circuit Open/Short to Ground.

An ALLDATA Tech-Assist consultant advised the technician that this A/C system uses a compressor with a variable solenoid to control compressor engagement instead of a traditional clutch. It will always appear to be engaged.

He recommended testing the A/C high pressure sensor. The black (BLK) wire was ground, the black/green (BLK/GRN) wire was B+ or battery power and the green/black (GRN/BLK) wire was the signal circuit.

The consultant further advised that once the technician verified that the power and ground were good at the sensor, he should back probe the signal circuit and monitor the voltage. If it was low, the sensor was probably shorted.

The technician inspected the wiring as advised and found power and ground to the high-pressure sensor was okay. When he back probed the signal circuit, there were only 0.04V. He verified that the signal circuit integrity was good.

Confirmed Repair: The technician replaced the A/C high pressure sensor (G65), cleared the DTC and verified that the A/C operated as designed. No DTCs returned.

Information provided by ALLDATA.

About the Author

Richard Diegle | Senior Automotive Editor for ALLDATA

Rich Diegle has been in the automotive industry since 1978. After graduating from a local community college, he began working at a Nissan dealership as a used car technician. Since then, he’s worked as a Nissan and ASE master automotive technician, shop owner, marketing copywriter, automotive editor, public relations manager, instructor, ALLDATA Tech-Assist team manager, and a senior automotive editor.