Folks, I have a 2001 300M that is having issues with the climate control. We've owned the car since new and it's always been a bit flaky when it comes to maintaining consistent cabin temperatures however over the past month or so it's gotten considerably worse.

Originally if you set the temp to say, 69 degrees the car cooled (or heated in the winter) nicely then after 15 min or so you would have to adjust the temperature because it would either continue to cool or heat. Somewhat of a pain but livable, you just had to tweak it a couple degrees occasionally while riding.

Now when you turn it on it's at the point where it could be 90 degrees outside and if you turn on the A/C it doesn't automatically switch to the max setting with the blower on high and the air coming out of the dash vents. Rather it might (you guessed it it varies) blow the air out of the floor vents and only be on standard A/C.

Everything seems to work manually just fine so I'm wondering if there is a module that needs replacing that contains the thermostat for the interior of the vehicle. Any advise is VERY welcome!

Thanks Jim

 

are u using the auto temp control or manual?

 

If I use the manual control, it works fine. When I use the auto temp control, it loses it's mind.

 

OK that's what I though
U dont understand how the system works then read your owners manual it will tell u in detail how it work and why it does what it does.

The temp coming out of the vents will not be what U set it at the infra red senors will see what the temp is in the cabin and it will then make adjustments from air flow to temp the out side or inside air and so on.
Get a thermometer and place it in the middle of the cabin and see what the temp is when U have it on auto for 15 min.

 

I had the same issue with a 2004 300m. There is a set of small louvers in the a/c control panel. In side is the cabin temp sensor. There was a small dust ball in mine which I believe blocked the temp sensor. I cleaned that out with a bent paper clip and that fixed my problem.