Heating controller “thinks” it’s too warm and brings cold air
 

The temperature controller is set to 70F and it works fine for while, like 10-20 minutes or less, I couldn’t figure out why it varies. The outside temperature is very cold, somewhere around 0F. Suddenly, the controller switches to cold air, “thinking” that inside is warmer than 70F. I go up to 80 and the fan spins faster bringing more cold air in. Again “thinking” the inside is very warm. So, no matter where I set the temperature, the system brings cold air inside. Up to here you may think it is the thermostat or air in the system but here is the trick. When I get the temperature up to 90F then I get heat. It seems to me that when I set to the max it does not care about temp sensors and it opens up the valves to let the coolant to travel through the core heater. I thought at the beginning that there is the temp sensor or little fan inside the controller and I opened it up and cleaned it. Before to put the unit in I also checked to see if it spins and it does. I cleaned the thermoresistor / sensor that’s in front of the fan as well.
I had no luck debugging this problem. I don’t know much about how the system works but I would count on your help to figure out what could cause this problem which is very annoying. The work around is to let it set for 90F and keep adjusting the fan speed which does not work very well since the airflow is dependent on the car speed as well.
Do you know if there are other sensors that I might need to check? I got it to the dealer and they want to replace everything like thermostat, valve controller, hoses, coolant temp sensors and a lot more up to $3000.

Thanks in advance for your help.

Nobody 's seen this pronlem before? or any tips would help. thanks

It must be somebody else that experienced this problem...

May be the ambient temperature sensor.

Do you know if there is more than one more temperature sensor inside the car? I checked the one in the heating controler and cleaned checked the sensor fan as well. The fan works but I don't know how I can check/test the sensor. Any tips?

what about the heater valve? it is DIY and a couple hundred bucks

I thought of that too but if the heater valve is stuck then it shouldn't open when I got to top temperature. Am I right? How do the heater valve act when it starts to malfunction? How can I test them?

I have a 2001 X5 and I get frustrated, because when it was so cold outside, it takes forever to warm up the inside of the car. I could even let it warm up for several minutes and no heat what so ever. Then, when my car would warm up, and I would be nice and cozy, I would have to stop at a stoplight and then my heater just went to cold air. The minute I started driving again, it would start to warm up....Not sure if this has anything to do with the post, but this is the closest thing I have seen, any suggestions? You all really know your stuff, and would appreciate any suggestions. Thanks

since it blows hot when driving/revving engine and cold at idle, first thing I'd suspect is coolant level. At higher RPMs, coolant flow is faster and can spill over into the heater core, then at idle, the level drops back down as flow through the radiator catchs up and the heater core gets starved.

one possibility (that's simple to check and fix)

- a -

Here is an update. Actually, the IHKA really 'thinks' that it's too warm and tries to cool off the ambient.
Using a GT1 I could read the inside temperature and it was 36C when it supposed to be about 13C. The problem was the the sampling fan inside the climate controller. This fan creates a draft through a temperature sensor inside the IHKA. If the fan does not spin then it get warm inside the unit from the electronic components which will make the controller to push cold air through the vents.
First you should try to clean the fan, next find a replacement fan or the IHKA module which is expensive. In my case the fan was sniping for a while and then it would stop.
Here is a link with what some of us did to fix it. I removed the fan and use a Hualingan fan from a broken unit.

I hope this helps other with similar heating problems. I replaced the control valves and there was no need for that. The old one was still good but the dealer pointed that to be the problem.
Climate Control