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Discussion Starter · #1 ·
07 M3 hatch with 275K miles.

Strange question right? It's happened at least twice maybe 3 times. I take it through the local Tommy Johns auto car wash. I get "The works" which sprays/washes the car from all angles including underneath. First time it happened, had it checked and freon was a little low. Happened again, took it back they said freon level was fine. AC started working again fine for two weeks. Took it through the wash this afternoon, and blam. Notice the air wasn't really that cold on the way home and it got progressively warmer. This is when it clicked that the car wash might have something to do with it.

Got home, popped the hood. Compressor is spinning, but no cold air. Is there any explanation for this? AC might start working in a day or two I guess but where would the car wash water be going that might cause this to happen?
 

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You said the compressor was spinning. Are you absolutely sure? Because you were probably just looking at the clutch.

Check your under hood relay, it may be going bad.

It's right next to the horn relay, and they are the same part number. Next time you have no AC, switch them, see if the compressor turns on.
 

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Discussion Starter · #3 ·
Are you saying the clutch can be engaged without the compressor running??

If i shine a flashlight down the left side of the engine, I can see the compressor at the bottom. The clutch was engaged and spinning. When it's not engaged, it's not spinning.

I guess I can't say for sure the compressor was running, but that the clutch was definitely engaged and spinning.

Already swapped those relays around, and no obvious signs of water in the relay/fuse box.
 

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Discussion Starter · #6 ·
I'll have to check that out. The water is doing something, I'm just not sure what. The shop that originally recharged the system and then checked it again suggested there might be something electrical going on, but I hadn't put my finger on the car wash yet. Would the OBDII system provide any info on the AC?
 

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I've had the same issue a few times with my '07 Speed3, but for me it happens on very hot days, and it seems to happen after getting held up in traffic. It just stops blowing cold air, and turning it on and off after traffic starts moving again doesn't help. I think damn it went out again, but the next morning it's blowing cold air again like nothing happened.
 

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I've had the same issue a few times with my '07 Speed3, but for me it happens on very hot days, and it seems to happen after getting held up in traffic. It just stops blowing cold air, and turning it on and off after traffic starts moving again doesn't help. I think damn it went out again, but the next morning it's blowing cold air again like nothing happened.
Best Guess..... with limited information and not physically checking the car myself..... This sounds like your super heat relay is shutting off the compressor. This is also a radiator fan related issue. Either your engine is just running hotter than it should (thermostat , coolant or water pump concern) or the fan is not doing its job or the super heat switch on the AC system is at fault.
 

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Superheated switch? Where in the system is this located at?
It also called a super heat sensor. You would need to look up in a factory service guide/manual where your specific one is located. And depending on your car may use a ambient Temperature sensor. Either or would be in the factory service manual and both can cause the AC to work inconsistently or not at all.
 
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