1990 525i - Confusing climate controls!

[Jesda]

I'm a bit baffled by the climate controls in my M20 E34 (wow, learning the lingo already). Here's what it looks like:

http://q.spilky.com/bmw/100_0174.jpg

Sometimes, when I turn both knobs to full heat, the two vents in the center won't blow the same air. One will blow hot and one will blow cool. Does this have anything to do with the red-blue slider between the two vents? I dont understand what it does.

Also, on the blower, what is the fan speed before "1" supposed to do? It seems to be on, but blowing very gently at the same speed no matter where I set it. Could buildup behind my evaporator be preventing the fan from blowing more air?

Thank you!
-Jesda

[Kalevera]

Well, the real problem is that you keep on thinking about that totally useless excuse for an automobile known as the Q45 :)

Most non microfiltered/early E34s have a mouse nest or two in the heater box (the theory here is that ones with microfilters get cleaned more often than not) which can stink up the air (egh!) and minimize air thoroughput. So, check for "backup behind [sic: actually, in front of] the evaporator."

The heat discrepancy could be a sticking heater valve, flap issue (unlikely) or potentiometer issue in the vent temp wheel (also unlikely since that pot regulates both sides). Searching "heater valve" will return myriad results, so do that first.


best, whit

[winfred]

the roller between the vents changes the mix of air coming through the vents in the dash, say your feet are cold but you don't want to roast your hands/face but still want airflow you turn the heat up and that roller between the vents to blue, air through the vents too cold but floor is good crank in a little more red, it's varly sensitive so you can adjust it to a good degree of comfort

[Alexlind123]

How does one go about checking for mouse nests? My fan is very weak and makes a noise deep throbbing noise when turned to full power, like that of a criuse liner's deisel engine. At three, the noise is not so prominent but the airflow is weak. Anything below three is useless. On an e28, the blower fan is where the expansion tank is on my car...

[tdgard]

How does one go about checking for mouse nests? My fan is very weak and makes a noise deep throbbing noise when turned to full power, like that of a criuse liner's deisel engine. At three, the noise is not so prominent but the airflow is weak. Anything below three is useless. On an e28, the blower fan is where the expansion tank is on my car...

Change your microfilter for the weak airflow. As for the grinding/throbing sound, wait it out. It may be that when you change the filter it goes away, but if it does not a new motor may be in your future. This should be a long time in the future. Mine made racket for years before finally giving up. Quite a simple process and only about 200 bucks.

[Jesda]

Well, the real problem is that you keep on thinking about that totally useless excuse for an automobile known as the Q45 :)

Only I get to badmouth my ex lovers! =)

Thanks for the help guys. :)

[Alexlind123]

Change your microfilter for the weak airflow. As for the grinding/throbing sound, wait it out. It may be that when you change the filter it goes away, but if it does not a new motor may be in your future. This should be a long time in the future. Mine made racket for years before finally giving up. Quite a simple process and only about 200 bucks.

ONLY $200? I pretty sure i dont have a microfilter.

[JonE]

1990 E34's don't have a microfilter, also, the HVAC system is a bit different as the older E34's have a "sword" final stage resistor that works to adjust the fan speed when you set the dial. Despite the fan number settings and the corresponding detente's, this is a continously variable fan speed. If you set the fan switch between two detente's, it will blow at a speed between the two numbers...Do a search on the topic and you'll find more info. also visit Bruno's site on this as well. Low airflow could be clogged heater core area on the non-microfilter cars, or, possible problem with the "sword". If you remove the sword you can kinda see whether the heater box area is clogged. Sword is on passenger side and tricky to get at (see Bruno's site). If air is cold on one side and warm on the other and your dials are set the same, check the water valve operation, located on driver's side under the hood near the firewall. You'll see two hoses coming out and going into the firewall for the heater core. Good write-up on that in Bruno's site as well.

[Striker169]

what year did the microfilter's get put in?

[Jesda]

Thanks Jon! I notice on mine, it blows cold until I switch off the floor and turn on the center vents. Very odd. But after that if I turn off the center vents and go back to the floor, it continues blowing hot air as intended.

When you refer to a clogged heater core area, youre talking about the area outside of it where things can build up, not the inside of it due to buildup of acidic coolant, right?

[SRR2]

I believe you don't have a microfilter and that's the problem. There's an accumulation of junk/leaves/rodent corpses/twigs/etc. lodged in your blower wheels and in front of the evaporator. The only way to deal with it is to open up the blower housing and shovel the stuff out, vacuum what you can, and try to clean off the evaporator to the best of your ability. This situation was CHRONIC on my '89 535 and was one of the things that finally swayed me to an E39 with its huge and trivial-to-change cabin air filters.

One technique I found useful to clean the evaporator was a portable steam cleaner. It's hot enough to sterilize the moldy gunk and doesn't produce enough water to overwhelm the drain. The steam temperature is well below the decomposition point of R12 by the way, so nothing to worry about there.