FYI: Fixing Climate Control Gremlins

[jb325]

I have a 1992 325i that I bought used. I bought it knowing that it had the following problems with the rotary style climate control. But, the guy that sold it to me said it was a stuck flap. NOT the case!!! Finally, this weekend, after a year of wondering what the problem is, I took it all apart and killed ALL the climate control gremlins. I am posting this because a few people have posted the exact same symptoms, but no one seems to have a fix. Here is the tale:

Symptoms:
1. Only got hot air through defrost and footwells. This happened regardelss of whether I set the climate control to the coldest setting or not. Even if the AC was on, defrost and footwells (if selected) were always hot.
2. Regardless of temperature settings, face level vents are ALWAYS cold. Even if the dial under the center vent is set to hot.

Solution (Two seperate failures):

1. This is caused by a failed heater valve. The heater valve governs how much coolant flows into the heater core. It is dual chambered, for the dual climate control, and has two solenoids which independently control coolant to each side of the heater core. The probelm is that they are not totally independent, as they have a common 12V source. In my case, this burned out internally, so even though I got 12V at the harness, I wouldn't get 12V to the coils. To test yours, locate the heater valve on the driver's side, in the engine compartment, attached to the firewall. Pull the 3 wire connector and test the pins. The yellow wire, when the climate control is on and set to full hot (last detent on the driver's side knob - you should feel a detent), should show 12V. Next, measure the impedence of the solenoids...Connecting an ohmmeter across Pin 1 and 2 and Pin 1 and 3 should show some impedence. If either one is an open connection, you found the failed heater valve. It makes sense that this would fail over time since it is always on, and in a hot environment.

2. This is caused by a failed Integrated Climate Control Module. NOT the control panel!!! I bet a lot of people think the control panel does the climate control stuff, right? NOPE! It does almost nothing, except to provide the inputs to the ICCM. The ICCM is located under the sunglass holder, in front of the shifter. It is a rectangular box with 3 wiring harnesses going into it (blue, white and black). The ICCM controls 3 servo motors that are attached to the heater box under your dash. There are two on the driver's side (dash vent mixing and recirculation) and one on the passenger's side (fresh air flap). The motor we are concerned with is the dash vent mixing motor. It is used to control the amount of pre-heater core air and post-heater core air to send to the face vents. It appears that the circuit that drives this motor has failed. This circuit takes inputs from a micro switch in the control panel. It is easy to locate: remove the control panel, and look at where the Bowden cable connects to the rotary knob. The other input is the dial under the center vent. When in the face vent position, check that the switch is open. If so, next, measure the impedence of the center vent dial. Total resistence (measure between Yel/Grn and Gr/Blk) should be 4.5k ohm. The wiper (measured between Br/Red and Br/Blk) should sweep the range 1.4k to 3.2k (hot to cold, repsectively). All okay so far? With the climate control on (engine off), and set to face vents, turn that center vent knob from cold to hot. You should hear the dash vent mixing motor (on driver's side of heater box - top motor) turning. It is moving the flaps from the pre-heater core position to the post-heater core position. If it doesn't do that, check that the motor works. To do that, check that the impedence of each coil is roughly 25 ohms. If the motor turns and you can rule out that the motor is working, then it is a safe bet that the ICCM is failed. Unless you feel like searching out the traces on the board of the ICCM, the wisest choice is replacment. I got mine for $75 from a junkyard.

One last note regarding ICCMs and 1992 vehicles...look at the numbers on the ICCM box. If you have "SW 10" on it, then you probably have a bad module. This apparently is a bad software revision and should be updated. I updated mine to SW 19 from a 1994 E36. Supposedly, this will also fix the problem of sometimes not getting any airflow at all from the face vents. The solution that works seems to be truning the car off, then back on. If that is the case, then upgrading to SW 19 will solve that problem.

Anyway, I hope this helped someone out. This was a pain in the butt to figure out, but after ripping apart the dash and studying everything, it's fixed. And just in time, too, since it hit 38 degrees tonight here in Boston.

[bungy42]

Sweet! Thanks for the info. I guess I either have to live with the problems or update the software on my ICCM. I'm not sure if it's worth the $75, though. By the way, which junkyard did you wind up going to? We had discussed this a while back, but never really came to a good conclusion...

[jb325]

Hey Bungy! Long time no chat. I went to Harbor Auto on the Lynnway in Lynn. I don't remember what the problem exactly was with your climate control. The first place I'd look at is the heater valve though. Then the ICCM. I have to say that $75 is a lot, but it is SO nice having heat again The other junkyard, by the way, is ABC in Leominster...They seem to have a lot of bimmers...

[MDRose64]

I checked out the yellow wire and I get a 13 volt reading untill I turn the dial past the last detent, then it reads 0 volts. Is this the way it should be? I just want to confirm, before I buy parts. Also I get no omm reading on one of the pins so I guess the heater valve is bad .

[everbruin]

i've symptom 1; is pin 1 the frontmost pin ie it connects to full yellow wire?
or does it not matter ie shoud every pin pair show resistance?
for 2k ohm setting, my
frontmost to passenger side pin showed .02; is this confirmation of a bad valve?
frontmost to driver side pin showed 1.6
passenger to driver side pin showed 1.6

ps thanks for great info above!