Subaru A/C System Dead, Compressor Won't Engage

I had a similar issue with my 2006 Impreza Diesel last summer and can share my experience with fixing A/C problems (medium experience level with car repairs). The A/C system completely failed to engage, and after some initial checks, I took it to a workshop. The diagnostic revealed an undervoltage issue that was preventing the A/C compressor from engaging properly. The root cause was a failing pressure switch in the HVAC system, combined with some wiring issues that were causing voltage drops. The total repair came to 240€, which included: Replacing the faulty pressure switch, Fixing wiring connections, Testing the A/C system, Checking for refrigerant leaks, Full system pressure test Before suggesting specific solutions, could you share: Have you checked the fuses related to the A/C system? Does the blower motor work when you turn on the ventilation? Are there any other electrical issues in your vehicle? What specific error code did your diagnostics show? This information would help determine if your issue matches what I experienced or if its something different in your A/C system components.

Thanks for the detailed response. My vehicle was last serviced at 34507 KM and the technician checked the fuses which were all good. The blower motor works fine on all settings. The error code points to low pressure in the A/C system. After reading your experience, I checked the connections around the A/C compressor and noticed the belt tensioner seems a bit loose. However, the main concern remains with the pressure sensor and pressure switch readings being inconsistent. The ventilation system works normally until I try engaging the A/C compressor. This makes me think its either the pressure switch or a failing compressor clutch causing the system to stay disengaged as a safety measure.

Thanks for providing those additional details. Based on what you described, your symptoms sound very similar to what I encountered, but with a slight variation. The pressure switch issue on my Impreza was initially misdiagnosed as a compressor clutch problem. However, the inconsistent pressure readings you mentioned strongly point toward a faulty pressure sensor or switch, which matches my experience exactly. When my A/C system showed low pressure readings, we first suspected a refrigerant leak. After proper testing, it turned out the pressure switch was sending incorrect signals, making the system think pressure was too low to operate safely. This false reading prevented the A/C compressor from engaging. While your loose belt tensioner should definitely be addressed, I dont think its the primary cause. In my case, replacing the pressure switch and recalibrating the system sensors resolved the engagement issues completely. The repair was significantly cheaper than replacing the A/C compressor. A proper diagnosis should include: Pressure testing the entire A/C system, Electronic testing of the pressure switch, Checking the compressor clutch engagement, Verifying refrigerant levels This systematic approach helped avoid unnecessary parts replacement in my case and might save you money too.

Thanks for the input. After considering the symptoms and your experiences, I've decided to book an appointment with a repair shop next week. The fact that my pressure switch is showing inconsistent readings, just like in your case, gives me a good starting point. I'll make sure to mention the error code and the pressure sensor issues when I take it in. The loose belt tensioner will also need fixing, but I agree its probably not the main culprit for the A/C compressor not engaging. I feel more confident now about what to expect and appreciate knowing that it might not require a complete A/C compressor replacement. Will definitely ask them to check the relay switch and run a full pressure test on the air conditioning system before replacing any parts. I'll update once I get it fixed in case anyone else runs into similar A/C problems. Thanks again for sharing your repair experiences, really helped narrow down the likely causes.