124 Climate Control....Please Help Me Understand
 

Here's what I experience:

1. AC works fine.

2. Heat works fine.

3. With moderate outside temperature (say, above 40F), everything seems to work fine: I can set a temperature, set everything to auto, and I will get variation in fan speed, variation in air temp from vents...things seems to settle at the temp I want...although I have noticed I have to set things pretty close to a fully cold position.

4. HOWEVER, when it's cold outside (this morning 25F), when the system is on it will always blow hot even after it warms up in the cabin. The only way to get cooler air is to click the wheel to the AC position.

What would/might account for this? Ordinarily with a problem like this I would think it's that temp sensor that goes to the CCU. But, as I say, everything seems to work fine above a certain ambient temp.

Thanks.

In-car temp sensor or aspiration of that sensor.

Check the aspirator tube. Also, hold a tiny square of tissue up to the aspirator intake and see if it stays sucked in place. If not, there is a problem. If it stays in place, the sensor could be bad.

In case you don't know where that little intake is...

You'll see a little square grill just to the left of the dome light. Place a piece of light tissue paper over the grill. If the fan is working, it will hold the little square of tissue paper over the grill.

Tiny piece of tissue paper stays in place.

If the problem is the sensor, then why don't I have the problem when the outide temp is above a certain point? That's the thing that confuses me.

Next time the car is acting up see if the tissue paper stays in place - the aspirator motor in my W124 was intermittent.