[1996 850 GLT] Trying to diagnose climate control problem

s2zeller · Post by **s2zeller** » 29 Apr 2012, 15:39

I have most of the under-dash off in an attempt to nail down why I get wildly different temp air coming out of passenger vs. driver's side vents. I am getting blinking AC/REC lights, but have not had them read yet.

I cleaned the grab-bar sensors last fall, and just checked the in-vent sensors (looked clean, but I swapped passenger for driver's side on the chance that one was bad).

I pulled the climate control from the console so I could see what I was fumbling with when contorted under the dash and found the following (with the ignition on but the car not running):

The flapper controlled by the passenger-side damper motor only moves in one of two cases:
- When the center CC dial is set to AUT and I'm changing the driver's side temp
- When moving between upper-vents-only (i.e. NW on the center CC dial) and AUT (and back)

I should note that I hear the recirculation damper motor when I move the passenger-side temp to very cold (I am doing this in an unheated garage where the temp is below 60).

The flapper controlled by the driver-side damper motor seems to only be working when the center CC dial is in AUT mode. When I am at upper-vents-only, I do not see any activity. If I flip between the two center dial settings, I quickly get to a blinking AC/REC light situation with the flapper vibrating a bit but not doing anything. Turning the ignition off and back on does see to clear it from this state.

Changing the settings of the AC or REC switches does nothing to affect the described behavior.

Is this likely the control unit, or are all of my damper motors (all original so far as I know) going south on me at the same time?

Or should I just get the codes pulled and act on that information?

Since I have it all apart, I'm going to pull one of the problematic motors to see if I can see anythin obviously wrong.

s2zeller · Post by **s2zeller** » 29 Apr 2012, 22:45

Didn't have quite the right tools (or time) for pulling a damper motor. I'll probably end up calling an independent garage to see if they can read the codes since I'm pretty much able to get them to fire by switching the center dial.

s2zeller · Post by **s2zeller** » 30 Apr 2012, 12:41

One other thing that I did do was to flip the duct sensors between passenger and driver's sides.

Apparently, that did make some difference (and now I'm kicking myself for not seeing how the dampers worked prior to the switch).

In any event, prior to the switch, the passenger side was blowing moderately cool to cold air while the driver's side was blowing hotter air (and often at higher volume)

After the switch (and I did blow off a faint bit of dust on each sensor, but nothing like the lint layer on the sensors by the grab-handles), the difference between the two sides is not so extreme and it is now the driver's side that blows cooler while the passenger's side blows warmer (but not the hot blast of the pre-switch driver's side vent).

s2zeller · Post by **s2zeller** » 09 May 2012, 06:59

Well, while changing the sensors did make a difference (and a new one is on order), the far left side (both of them) started blowing extremely warm air at high volume just after the REC/AC lights started to blink (AC was off at the time due to the constant cycling of the compressor... new refrigerant is also on order).

While slightly warm, the left center vent was closer to the correct temperature being wafted out the passenger side vents.

I'll have to look at the list of codes that were pulled this weekend.

s2zeller · Post by **s2zeller** » 18 May 2012, 06:05

The code list was not helpful. Some looked like ECC codes, but some did not. I had them read at a friendly independent, but I don't want to abuse their generosity.

I added a can of refrigerant, so now I can get the two extremes fairly reliably. It is the middle zone that is difficult (i.e trying to stay at 72 when that is about what the outside temp is), with the far left vents blowing high volumes of hot air from time to time. When I was driving the car, I'd just switch AUT off and fiddle with the control manually, but the current driver doesn't want to be troubled to do that.

A chirping/squeaking sound is occasionally being noted and seems to be coming from the ventilation system (hard to know where). I recall this before, but it is definitely not consistent. Next chance I get, I'll have to try and pull some of the damper motors.

Post by **Ben850** » 18 May 2012, 07:37

Do you know if your ECC unit is good? If the codes you are getting do not seem to apply, that may be the problem, and it's easier to change out the ECC than to mess with sensors and duct motors. Less expensive as well if you can get a salvaged ECC that is known to be good. It worked for me.
Good luck.

s2zeller · Post by **s2zeller** » 20 May 2012, 12:16

Ben850 wrote:Do you know if your ECC unit is good? If the codes you are getting do not seem to apply, that may be the problem, and it's easier to change out the ECC than to mess with sensors and duct motors. Less expensive as well if you can get a salvaged ECC that is known to be good. It worked for me.
Good luck.

No, I don't... and I'm strongly beginning to suspect it given the erratic behavior. However, the change in behavior due to a sensor swap and the chirping noise suggest to me that there is more than one thing going wrong.

s2zeller · Post by **s2zeller** » 24 Jun 2012, 09:05

I pulled both dampers on the driver's side and they both functioned when removed (i.e. not screwed down, but still plugged in).

The upper (from my understanding) is the driver's side temp damper, and I see that fits into a black plastic shaft. Using a telescoping mirror (and by touch), it didn't see me to be cracked at all.

However, I am wondering if there is another way to get to it (other than taking most of the underside of the dash out) so that I can verify that (since I'm only seeing the end and not any of its lenth).

s2zeller · Post by **s2zeller** » 24 Jun 2012, 21:06

I found the inner cabin temp sensors (behind the grab bars) to be much dustier than I thought so I took them out, cleaned them, and swapped sides to see if that alters the behavior.

s2zeller · Post by **s2zeller** » 25 Jun 2012, 20:36

No change in behavior with swapping the sensors. The far left set of vents blow very hot air when I increase the temperature from 72 to 74 (used to do it when changing from 80 to 82) while on AUT. The center driver's side vent might be blowing slightly warm, but this is not clear. The passenger side continues to blow cooler air.

So, this seems to leave the following as possibilities:
1) Bad ECC
2) Stuck damper door (where?) and/or sSplintered damper motor shaft (if so, how do I get to it without taking the whole dash apart)

Am I missing anything?