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1999 BMW M Coupe Heat/AC issues

hey guys, i need some help with my '99 BMW M Coupe. this car is almost ten years old, but only has 40k miles. anyway, on with the question:

in the summer, with temp. controls set all the way to cold, but with the A/C off, i get super-cold air blowing out. after about 20-30 minutes of driving, the air stops coming out, even with the fan control set to maximum. typically the blower won’t start working until the car has been turned off and restarted, sometime later. also, even though the air coming out (when it’s working) is super cold, the A/C isn’t on. when i turn it on, i hear the compressor kick in, but the air gets no colder, which is good, because if it did i’d freeze my hands to the steering wheel. however, when i park, i have a long stream of water coming from under the car, indicating to me the compressor/AC was running. but according to the A/C button in the car, it was most decidedly not on.

in winter, the exact same thing happens with the heater. blows for a while then shuts off completely. of course, when i took it to a mechanic they couldn’t get the problem to duplicate (mainly because they didn’t drive the car for 20-30 minutes. they said they’d do it next time i brought it in. but, being that this is a BMW, having them diagnose gets very expensive at $100/hr labor rates. PLEASE HELP!

I am going to answer your question assuming it is a E46 and your concern is intermittent blower operation am I correct? If so these cars have a problem with a electrical component known to BMW as “the final stage” it is a solid state device that regulates blower speed. Very common to fail. It is located inside the car on passenger side by the right hand side of the center console. It is a rectangular alluminum component with cylindrical aluminum heat-sink tubes its held into the evaporator housing with 3-4 small screws (torx head)and has a group of wires plugged inti it, mildly difficult to remove (some reciruc. door linkage partially in the way its a little tough for the non BMW DIY kinda hard to get the final stage to go fully back into the evaporator housing,easier to remove-install if you leave the connector plugged into it (sorta like a handle)The e39 (five series)of this year had the same final stage same concern,was easier to change. Post back if I have the concern type of vehicle correct wnen you say M Coupe I am thinking 2 door 3 series and concern is with the blower.

It sounds like you may have a couple of things going on here.

I’m too lazy to look it up, but wasn’t the M3 model still an e36 chassis in 1999? If so, I know a lot about e36 because I still own two of them.

Blower problems are usually due to a failure in the resistor pack that is next to the passenger’s left foot, as I recall. It is easier to replace than the comperable part on an e46.

Temperature control problems could be due to a failure of the fan that pulls cabin air through the climate control. That fan is available as a separate part from your BMW dealer for $65. If you have owned the car for some time, you have heard that fan continue to run after you turn off the car. If you have not heard it lately, that could be your problem.

The #1 most common problem with late e36 climate control systems is the capacitor on the circuit board. Your dealer should know this, though their solution will be to sell you a new $500 climate control. You can fix it with a $1 capacitor and a soldering gun. If the fan, temperature, and lights on the climate control are all acting crazy, this is your problem. I have posted instructions for the fix on my web page.

Could be very possible M3s in 99 were on E36 chassis. Good call but wasnt the E36 final stage on the drivers side? I remember the display on the head going wild but did it also affect the blower.Do new control systems need to get coded to work I seem to remember yes and no

Not sure what you mean about coding the control system. I don’t think there is any firmware to speak of in the climate control. You may well be correct about the location of the resistor. I have not changed any (yet).

Coding is how you tell the GM (General Module) to recognize a component controled by the cluster or the GM. I will check with my source and post to you tomorrow. I got curious after viewing your control head site.

Are you involved in BMW repair? i used to be a dealer tech,retired now,still have good contacts with Master Techs from BMW if you need any help I will give you my E-mail address I am just trying to keep my brain active.This reply for Manolito

Source tells me heads need to be coded or they would read in celcius

all-- thanks so much for trying to help me with my car issues. sorry i haven’t responded, i’ve been on vacation. this car is not an e36… rather it’s the same body as the z3, but it’s the hatchback, not convertible. i hope that helps a little.

this does sound like a final stage problem to me. but would that explain the condensation coming from the AC compressor, even when the AC is not on?

(thanks again for taking your time to respond!)

You are correct-no condensation from ac compressor? when not running. Are you sure you mean compressor and not evaporator?(the part that is inside the car) Z3 evaporators are the easiest of any car I ever did to change(I know your not saying you are having trouble with a leaky evaporator)And you are correct Z3’s share many parts with the E-36.Not the same body but many chassis parts. I think there are some rear suspension parts different on a E-36 than a Z3

hmm, that’s a good question. i’ve never actually crawled under the car to see where the stream of water/condensation was coming from. i assumed that since i was also getting condensation on the dash that the AC was indeed running (even though it was not turned on).

so it’s possible it’s not coming from the compressor?

It is very possible that your compressor runs even if you have not selected it to.Your getting condensation on the dash or is water vapor blowing out the air vents. I dont know what to say about condensation on the dash but water blowing out the air vents is definietly not normal and it means your evaporator housing is not draining.You say you do see water under the car at times? The compressor does not leak water.Condensation(water)does collect in the evaporator housing this is a normal situation.It should be able to drain off on to the ground,if water is comming out your vents and you dont see any on the ground your drain is very blocked.I will post back directions on how you can find your evaporator housing drain,they are usually not hard to find,look for a little rubber hose pointed at the ground attached to the firewall on the passenger side of the car.But I will ask exactly where it is.

My source says your evaporator drain is above the transmission

I hate putting any of my addresses out on the web, but I have a hot mail account that I’ve not used in years so I will put that here and try to remember to check it over the next week or two it so we can link up and share the wisdom of our combined years. It is Manolito nine eight seven six five four (numerals).

I am a mechanical engineer who worked his way through college as a mechanic and auto mechanics instructor in a high school and a junior college. Before I did that, I was a motorcycle mechanic.

Based on what you’ve described, I’d guess that either you have an electrical problem that’s causing the compressor to run all the time (or since you can “hear it kick in”) that the compressor clutch is seized, and all you hear is the click when you turn it on. With the compressor clutch seized, the normal A/C system controls can’t control the operation of the system, so it runs at full blast all the time until the evaporator core completely ices up, causing the air flow through it to be blocked. After the car sits for a while, the block of ice melts and you have air flow again. This is also supported by your describing a long stream of water running out after it’s parked. Not only is this not good for the A/C system, but it’s probably giving you really lousy gas mileage.

The iced up evaporator is a very good thought.