98 S70 T5 Climate Control Fails to Control Heat After 15 min

sendres · Post by **sendres** » 27 Nov 2012, 21:44

Now that the weather in Chicago is turning to winter, it's time to address a problem that began last year...

My 98 S70 T5 is having an issue with the climate control system. On a typical morning (say 32F) I'll set the climate control for 72F and the fan speed to Auto. At first, the fan is off due to the cold engine, but within about two minutes the blower speed begins to ramp up. As I continue driving, the fan and heat output reach full speed and quickly heat the cabin. Within minutes, we're stabilized at the desired temperature. So far, so good!

But after around 15 or 20 minutes, the climate control seems to go haywire and the air output turns cold. Adjusting the temperature dial has no effect. The only way I've found to maintain comfort is to set the temperature controls to the max heat setting (red dot) and to regulate the level of heat with the Manual rage on the fan speed control.

So, a few key points to recap:
- At first, the climate controls work entirely correctly in regulating the fan speed and heat level in brininging the cabin to temperature.
- Once the heat shuts off, I can get plenty of heat on the max heat (red dot) setting with the manual fan control. So the heating system is clearly still capable of heating, it just "chooses" not to.
- If I shut off the car briefly (for example, to fill up on gas) the heat will not come on by climate control when I resume driving. But if the car is off for a few hours, the climate control will again function normally--well, for another 15 minutes or so!

Any thoughts? Thanks in advance for any ideas you might have!

Post by **jblackburn** » 27 Nov 2012, 23:22

My first idea would be to take a can of compressed air and blow out the temp sensor near the sunroof/info/defroster switches. If that fails to make a difference, the sensor itself may be bad.

Post by **jreed** » 28 Nov 2012, 04:50

It sounds like you have the ECC system. Are you getting the blinking "AC / REC" lights on the front panel?

Post by **cn90** » 28 Nov 2012, 05:31

Another option is to slide the switch to the right (manual control).

Post by **rmmagow** » 28 Nov 2012, 06:46

This morning mine sort of behaved strange too. I had the fan set to max speed manual to defrost the windows. The AC/REC lights were blinking. I set the temp to 72, directional thing to AUD and moved the fan lever to the automatic setting and the blinking stopped and the system worked as expected. The only other weird thing I've noticed is that once in a while with everything set to automatic, the fan will speed up, slow down, speed up, slow down in pretty short time intervals. All this strangeness is from a cold start, 20~30 degrees F. I generally start the car and let it warm up for a few mins and all is well by the time I get in to drive.

Post by **jblackburn** » 28 Nov 2012, 07:03

cn90 wrote:Another option is to slide the switch to the right (manual control).

Doesn't help if the temperature controls themselves aren't working. It'll still just blow cold air at you.

The only other weird thing I've noticed is that once in a while with everything set to automatic, the fan will speed up, slow down, speed up, slow down in pretty short time intervals.

I've had that happen. And on AC mode when the interior got nice and cold, it would randomly ramp up the fan and blow HOT air at your face. The only thing I could figure? These cars are crazy.

sendres · Post by **sendres** » 28 Nov 2012, 18:18

Yes,my car has the electronic climate control. I believe I have seen the lights flashing for a few seconds, but only upon starting the car. I will try cleaning the temperature sensor as suggested to see if that makes a difference.

sendres · Post by **sendres** » 29 Nov 2012, 07:33

SOLVED. Blowing out the sensor seems to have fixed the problem. Many thanks for the helpful suggestions!