AC compressor noise only when car is hot

Question

I recently noticed that my car is making a consistent noise when AC is engaged. Furthermore I found that this noise occurs only when car is hot. Belt doesn't seem to be slipping.

Car is 16 Subaru WRX. Found several similar issues online for Forester and Crosstrek though. Here's one similar noise problem on a Forester https://www.youtube.com/watch?v=cQJuVlMgGJs

Nobody seems to have a clear conclusion of reason or fix. Before I take it to the dealership and spend $1,200 for a new AC compressor, is there any budget friendly fix I can try at home?

Al_ · Answer

The noise in the video sounds like a scroll/vane compressor lubrication issue to me rather than a worn compressor per se. The refrigerant is what brings the lubricant around the system whenever the compressor lacks a sump so less refrigerant means less oil returning back to the compressor.

You might be either low on refrigerant or compressor lubricant or both. You might try having the system tested for leaks and the original refrigerant charge restored if no leaks are found and see if it somewhat reduces the noise.

Keep in mind that scroll/vane compressors are less tolerant of reduced lubrication than piston ones, so the compressor might be already damaged.

Try also letting AC run with max heat, recirculation hot and max blower on on a warm engine and see if the noise is different from when you run it on max cool, recirculation on and lowest blower speed.

AC compressor noise only when car is hot

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