Always hot - HVAC ambient temperature sensor

Hi 8ers,

My HVAC is playing up, I'm getting hot air from some vents all the time (even with the driver temp on max cool). I know this stinks of heater control valves but I replaced these a few years back so I'm thinking it's something else (i've ordered a 12v probe that I'll use to rule out the valves). I connected DIS (still blows me away how much info that gives for a 1991 car) and ran some diagnostics. There was an error regarding ambient temp sensor, and when I saw the values returned by the various sensors the ambient sensor showed 0c. According to the HVAC manual this is the default when the sensor is broken. Whether this is the root cause of the hot air or not I ought to get it sorted so does anyone know where this sensor hangs out? I can't find it on realoem.

I know there is an ambient temp sensor in the air intake in front of the passenger front wheel, but I think that's for engine management or just for the MID??

I'm really enjoying my car now and am driving it every week. There are a few fairly significant problems that I need to solve to make it more liveable but the heater being jammed on is right up there so help me out 8er heroes

Thanks Timm. Does my head in when replacement parts start failing but I guess they are not immune from problems. I've got a feeling I'm in the unlucky 1% but I'll know later this week.

I messed about with it on my way to work this morning and it's more mad than I first thought.

The face dash vents and the main ones on the door blow slightly warm (warmer than ambient, but in no way hot) regardless of temperature setting. I tried max hot and max cold and it made almost no difference, this was with the all vents open setting. The defrost vents on the dash and doors blew warm air (warmer than the face vents) on max cold and hot air on max hot. If I changed the vent setting to footwell only, I only got air in the footwells (except a tiny amount out of the defrost) and it was full hot, regardless of temp setting (I tried max cold, max hot and settings in between). Not sure about the passenger side as I was driving and my arms weren't long enough.

When I started out this morning the system was off and temp was set to max cold. I was getting a small amount of warmish air out of all vents and a weird whistling sound from behind the dash. One I turned the system on (via the fan control) I heard the steppers all do their thing and the face vents became significantly cooler (still above ambient).

Do my ramblings give anyone any idea? It's lost its marbles hasn't it....

I get that but even stuck heater vales don't explain the mad behaviour mine is showing (I don't think). My 12v probe thing will arrive today or tomorrow, after that I'll follow Frankie's diagnostics and let you all know what I find.

I've started driving my car a lot more and this is really doing my head in. I'm almost certain it's the IHKA control module which has made me sad as they are super pricey. The valves are fine, they just seem to get strange messages from the controller. Anyone know where I can get one? The only one I can find is over £300. https://www.ebay.co.uk/itm/bmw…2bdba1:g:YToAAOSwuShainrU