Air conditioning not cooling
A/C blows warm or barely cool air — checking via OBD-II and spotting a refrigerant leak.
The A/C system is one area where OBD-II genuinely helps. Most modern cars use ECU-controlled compressor clutches with pressure-based safety cutoffs.
Causes: (1) low refrigerant pressure from a leak — compressor shuts off by safety switch; (2) faulty compressor clutch — you hear the click at A/C-on but the compressor doesn't engage; (3) dirty condenser (in front of the radiator) — poor heat exchange; (4) faulty A/C temperature sensor.
OBD-II may show B1 codes or a Climate Control Module fault. Check the AC Request PID — does the ECU see you requesting cooling? Also check RPM with A/C on vs off — a 50-150 RPM drop is normal when the compressor loads up.
First diagnostic steps
- Visually verify the compressor clutch engages when A/C is on
- Measure system pressures (manifold gauges): LP ~20-40 PSI / HP ~175-250 PSI
- Read OBD-II B-codes and check AC Request PID
- Clean the condenser of bugs and debris
- Check the compressor clutch fuse and relay
Likely fault codes
B1000P0532P0533P0534B1485 Click a code for detailed description, causes, and diagnostic plan.