Last year while trying to improve the anemic air conditioning in my 2004 R53 with 120K I tried one of those DIY refrigerant-in-a-cans. While following the directions, and monitoring the pressure on the can's gauge, there was a sudden 'pffft' from the vicinity of the compressor. It sounded as if some pressure relief valve had been actuated. Thereafter the system lacked any cooling whatsoever, although the compressor still engaged and ran normally, which says to me that there remains enough refrigerant in the system to satisfy the low-pressure sensor and that the clutch is not bad. I took it to the dealer and they told me nothing other than the compressor is bad, and would cost $1,500 to replace.

Before I do anything to get this working again, is anyone aware of any such relief valve on the compressor, and if so is it a repairable part?

TIA.

 

No relief valve that I know of.
Is your low speed radiator fan working? I replaced the compressor myself for <$400 several years ago. $1500 is about right for dealer, independents will be $900-1100.

 

Yes my low speed radiator fan is working.

 

An AC shop should be able to test it, but it you've got refrigerant, and the clutch is functional that says bad compressor to me.
In my case the low speed fan went out, and it is postulated that the AC compressor overheats at low speeds because the fan is not on to cool it.

 

Next question: what are the chances that the expansion valve has also gone bad?

 

That's another issue I've heard of, but I went straight to the compressor, which fixed the issue. Not sure of the diagnostic steps to test for the expansion valve function.