AC going hot & cold

[Ahmedg]

I've been having problems with my air conditioning for a while. When I'm driving, especially when I put my foot down on the accelerator, I feel the AC going warm for a few seconds and then go back to cold again. And there's a slight damp smell that accompanies it. Sometimes it's so slight, that I barely sense it. But sometimes it actually goes hot for a while. Last week I was washing my car and after the wash the AC just started blasting out hot air for about 40 minutes and then became cold again. What could be the reason? Also my horn sounds really low and funny after the car wash. The engine was running when the car was being washed at the beginning, then I turned it off. Could that have anything to do with it? Thanks

[akanso]

When u press full on the accelerator the compressor goes off for like 5 seconds because to give the car full power.

Have u washed the engine with direct water?????

[Ahmedg]

No I never wash the engine, just the body, but I thought perhaps some water got in through the radiator fan.

[akanso]

Ssnese, did u by any chance heard something like this or happened with you???

Let the memebrs who own e39 M5 deal with this, they are more experienced with the e39 M5.

[Ayham]

I'd look for the fuse map (I would've told you the fuses locations if I had access to it) and find out which fuses are for the AC compressor and AC control unit. More than probable, your problem seems to be electrical. On older BMW with knob control units we usually find it's the copper board (don't know it's technical name, sorry!) under the knobs that's busted.

This is especially suspicious since your horn is affected as well around the same time....I very much doubt it's the compressor itself dying out. How much mileage?

[Bruno]

i'm not sure about the smell, you might wnat to change the micro filter which is 35 dirhams for 3 series, could be a bit more for yours.

the cold/warm air is usually due to the ac gas, you gotta check that out.

the horn has nothing to do with the AC, it just got in some water and when it dries out all will be back to normal. 2 months ago my horn got in some water from the rain, luckily i managed to reverse out of the pond quickly and save the car from further damage. the water dried out after 2 weeks from the horn. lol

[SSense]

A quick check for the air-con side would be, find the high and low pressure pipes in the engine bay, if all is well with the air-con one should be ice cold with condensation forming on it and the other should be hot, maybe even too hot to touch. If this is not the case it would suggest a fault somewhere within the air-con system.
Worth also checking that the electric fan is running whenever the compressor is engaged as this is critical to get the heat out of the air-con circuit.
Is the compressor cycling on and off or is it running continually? If it is on continually then this could be a sign that you are low on gas. I think it is a pressure switch that cycles the compressor so if you don`t have enough gas the pressure can`t be achieved to switch it off.

Lastly, when was the last time that you replaced the microfilters? If they are very dirty, they will definitely affect a/c operation and the bad smell..

[M5drift]

regarding the smell , it could be the A/C radiator. r u seeing some sort of vapor inside the car ?

[Bashar M.]

Ok you need to top up your AC gas, and the smell is bcz ur AC microfilter needs to be changed.

[Ahmedg]

Hey thanks for the tips guys. Sorry I've been offline for a couple of days. Well the microfilters just got changed about 10 days ago or so, and the ac warming up is intermittent. It doesn't always happen, but at times it happens quite a few times over a short space of time. It hasn't happened to me for the past few days though. Also the horn is still sounding funny, I don't know if I need to fix it or something. I'll check the fuse box as Ayham said.

I haven't read all of the posts up above, but I had this same problem with my 7.

The air con ended up being low, and there was also a leak in the line. You might want to go to a local BMW shop or mechanic and have him/them check it out real quick to make sure this isn't the problem before you go fixing a ton of other stuff.... not that that's a bad thing though.. :wiggle: