AC doesn't work. Any ideas?

I took the car to an AC/Radiator shop because the AC isn't working (button lights up but no cold air) and I was hoping it could just be refilled with freon. Air blowing in car just in general seems a lot warmer even with AC off but maybe it's just in my head. Tech said the high side pressure seemed good and he couldn't get to the low side without taking the air intake out and he didn't think that was worth it because he suspected that won't be the problem and suggested I take it to a BMW specialist.

So now I am going to attempt to figure out what's going on myself before taking it to anyone. I don't recall the last time I used AC and it worked because I didn't have a need for it until now in the summer months but it did work when I bought it late 2019.


Scanned the car for codes and it has Code A670, signal above threshold. Apparently this is the condensation sensor between the rear view mirror and the glass. Sensor is cheap enough I'll probably attempt to fix it in the off chance this is related?

Also the seats were swapped in the past and now I have heated front seats so I needed an HVAC with the correct buttons. Bought one off Ebay and didn't actually test if AC worked after that, just saw the button light go on and assumed it worked. So maybe I should swap back to the old one and see what happens. Could I have shorted out something during the swap?

Fuses are something else I can check. I did verify there seem to be fuses where there should be for AC to work but not sure if they are blown or what so I'll just swap for all new ones anyway.

I also installed a new plenum so I guess it's possible I hit some kind of sensor in the engine area that would throw the AC out of whack? Not aware of anything here that would stop the AC from working.


If I can't figure it out will a BMW specialist be able to pull more specific codes than the A670 I am seeing? That's all I see.

Any suggestions?

The HVAC control module in the cabin can cause issues with temperature. I had a problem in the past where my ac would stop blowing cold air intermittently, usually after the car had been running for a while. No error codes, no issues with condenser or gas pressure. Turns out the HVAC control module was faulty, and replacing it with a used unit fixed it immediately.

That said, there are many different versions of the HVAC control module and only the specific one works with your car. I would try to swap back the old module first and see if that solves your ac problem.

If the high pressure side is good when it's running then your compressor is coming on but probably pumping air. Some compressors have low pressure cut off switches on the low side and will kill the compressor if it's low on r134. I don't recall if BMW's do or not. Your low side stub is right there behind bank 2. Sounds like the tech couldn't find it? You don't have to remove the plenum to get to its. When your ac is out of gas you can hear it in the cabin too.. sounds like an air leak as a little bit of gas is bubbling off in the evaporator when it's on

Redd wrote

The HVAC control module in the cabin can cause issues with temperature. I had a problem in the past where my ac would stop blowing cold air intermittently, usually after the car had been running for a while. No error codes, no issues with condenser or gas pressure. Turns out the HVAC control module was faulty, and replacing it with a used unit fixed it immediately.

That said, there are many different versions of the HVAC control module and only the specific one works with your car. I would try to swap back the old module first and see if that solves your ac problem.

Well mine is a fucking X3 one lol so maybe that's the issue. I could just get the lower buttons below the hvac that control heated seat and put back my old HVAC. Or actually get the one from an M3 or e90 with heated seat buttons. Guess I will make sure the e90 version is the same as one in M3 before I do that.

I KNEW I kept my old HVAC controls for a reason!

I have the same issue w my M3. Recently had the compressor replaced by a local shop ($2700) and month later no cold air. It also does not blow with the same power.
Took it back to the shop, they said compressor is ok but I might have a leak that would require removing the dash to get to it...

The BMW tech did the recal on the blower motor wiring today too after they diagnosed it is a leak.
What a mess.. probably looking at a crazy repair estimate. Will get it tomorrow.

Any other way to fix this?

I hate to mention this possibility, but there is a known A/C issue with BMW E9x M3's that the evaporator will fail
It's a $100 part, but it's down underneath the middle/bottom of your dash, which means to replace it you have to take apart the ENTIRE dashboard
A very difficult time consuming process, and the labor for that alone can run into thousands of dollars

You can do your own search, but I'll provide a couple of links below to get you started:

https://www.m3post.com/forums/showthread.php?t=1120670

https://www.m3post.com/forums/showthread.php?t=1723803


I hope I'm 100% wrong but wanted to mention it in case it helps diagnose the issue.

SRB_Mpower wrote

I have the same issue w my M3. Recently had the compressor replaced by a local shop ($2700) and month later no cold air. It also does not blow with the same power.
Took it back to the shop, they said compressor is ok but I might have a leak that would require removing the dash to get to it...

The BMW tech did the recal on the blower motor wiring today too after they diagnosed it is a leak.
What a mess.. probably looking at a crazy repair estimate. Will get it tomorrow.

Any other way to fix this?

a/c techs that dont work on BMWs usually don't know what they are doing.

I had to show one where the low side connection is. It's under the plastic where the Cabin filters are, takes two minutes top the covers up to get to it.

He kept saying there is nothing wrong pressures look good, I said forget your BS, evacuate the system and then recharge it. I will pay for if even if it doesn't work after.

He did what I asked and was somehow amazed that it was working.
He was previously trying to tell me it was the compressor, or could even be the condenser. Which didn't make any sense.

Redd wrote

The HVAC control module in the cabin can cause issues with temperature. I had a problem in the past where my ac would stop blowing cold air intermittently, usually after the car had been running for a while. No error codes, no issues with condenser or gas pressure. Turns out the HVAC control module was faulty, and replacing it with a used unit fixed it immediately.

That said, there are many different versions of the HVAC control module and only the specific one works with your car. I would try to swap back the old module first and see if that solves your ac problem.

Guess I never replied to this thread I created with the "fix"

swapping back to my old HVAC unit fixed the problem immediately. So either the used one I got isn't a model that works with an m3 or it was faulty. My guess is the model I got doesn't work with m3. So for now I saved myself $3000 for an evap fix, but lost heated seats because my old HVAC doesn't have the buttons, so I'll either find an HVAC control unit that works or just get the piece that connects to it and adds the row of lower buttons with heated seat buttons.

Ok great news for not having to replace the evap

1 down, 1 to go ...

akkando wrote

Guess I never replied to this thread I created with the "fix"

swapping back to my old HVAC unit fixed the problem immediately. So either the used one I got isn't a model that works with an m3 or it was faulty. My guess is the model I got doesn't work with m3. So for now I saved myself $3000 for an evap fix, but lost heated seats because my old HVAC doesn't have the buttons, so I'll either find an HVAC control unit that works or just get the piece that connects to it and adds the row of lower buttons with heated seat buttons.