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If the compressor is running the relay should be ok. The ehc control unit has a timeout function to protect itself from burning out which it doesn't do very well. If the compressor can be heard without listening hard it has probably failed, they become noisy when overworked.
I suspect the ehc knows the compressor is not inflating the bag and turns it off.
The compressor has a hard plastic piston ring and when bags are slightly leaky the compressor has to over work but not to the degree to timeout so it wears prematurely. There is also attached to the compressor a valve block that get stuck and won't let air in or sometimes out.
I would guess at some point the bags were leaking for a while gentry before replacement which wore the compressor early now it's just failed.
As an aside all the aftermarket compressors are much cheaper but usually come without the valve block so if this the issue that needs changing too. The genuine bmw ones are expensive but come with valve blocks. Valve blocks not available as separate part from bmw but can be found on eBay etc.
If it was me I would get a quality replacement compressor like bilstein or arnott and a valve bloack from eBay and replace as one.
Also bear in mind there are two valve blocks as some ehc pipes are different sizes.
I have changed loads of these bags and only once did I do it as per instructions where I cut the pipe and pushed it in and that was the only one that ever leaked. I always undo the brass fitting with a 10mm from the old bag then hand tighten it into the new bag as to not pick up the plastic threads (the air pipe makes it feel funny going in) then nip up with a spanner.
Always spray the system with soapy water and check for bubbles forming, if you can't access use your phone camera to reach.
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