A/C fan / settings question for W126 '84 300SD - PeachParts Mercedes-Benz Forum

bodyart27 · #1 06-11-2003, 09:22 AM

I'm thinking in my attempt to remove the center consol, something might have come unplugged on the A/C controls.

If on defrost - I can punch the high fan and it blows hard (so the blower is working - right?). On the regular A/C setting I can get the A/C to kick in, blow and cycle on and off by moving the temp wheel to the left, but I can not get the high / low fan to engage on normal A/C. A/C was recently filled, so when it does come on, it's cold. Weird huh?

Any thoughts?

sixto · #2 06-11-2003, 01:02 PM

I'm not sure what you're saying. In defrost, the blower should go full tilt regardless of the fan switch setting. If you can control the blower in defrost mode, something's wrong... though I'd say you're one up on MB since MB generally doesn't like to delegate control.

Are you saying that the AC only blows when the fan switch is on auto? If it doesn't work on low then maybe there's a bad resistor in the blower control resistor pack. But all the resistors are bypassed in max so it can't be a bad resistor.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

bodyart27 · #3 06-11-2003, 04:11 PM

Thanks for replying. Disregard the first post (especially the defrost comment – it was the bi-level button – thus why I could vary the fan speed). I did not give you a whole lot of information, so let me try again. The car was my mom's so I have not had a lot of seat time understanding the operation. Maybe the following is normal.

When I dial in the temp between 18*- 20* C and just leave it alone in "Auto" using the normal A/C button (one white arrow), the A/C kicks in fine, will vary the blower speed as needed to cool the cabin, side and center vents blow, then "click" - it shuts down 100%. When I mean 100% you can not get the high or low fan to turn on at all. Just still dead air in the car until the temp rises again, and you hear the "click," and the A/C slowly kicks in again, varies the fan speed as needed, the “click” – it’s off 100% again.

Now while it is on this cool down cycle and the A/C is blowing you CAN cycle the high / auto / low, but once it cools off - "click" - dead still air - the fan speed buttons will not respond. It does not matter if I hit / cycle the "O" off button and then the normal A/C button or any combination of the fan buttons (high/auto/off). No A/C until the temp rises in the cabin past where I have it dialed in on the wheel. While cycling between normal A/C and Off I think I can still hear the compressor engage, just nothing blows.

I did try the following. If I left the fan on high during the cool down cycle, it would cool down on high fan speed, cut off, dead air (temp rises in car), then the A/C would "click" and recover on the "high" setting.

While on the cool down cycle if I switched the fan setting from "auto" to low - it seemed that the A/C would stay on (I had to get back to the office so I could not give it a lot of time), but it seemed to stay on and never “click” off. That was about 5 minutes where before it would cool the car down and switch off in about 1 minute.

I guess I am just used to “auto climate” A/C systems that never 100% shut down but vary the air temp AND fan speed to keep the cabin cool. I’m always used to some degree of cool / cold air blowing on my face so when the air flow stops – it’s really odd to me. I don’t remember it operating like this before.

So, is this normal?

sixto · #4 06-11-2003, 04:32 PM

That's a tough one to follow but here's my take -- the fan should not stop while the ACC is on. My rough guess, and it's very rough, is that your fan brushes and/or bearings are worn and it's hard to keep the fan turning slowly and it can't quite pick up again once it gets to truning slowly. Could also be dead resistors in the resistor pack.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

bodyart27 · #5 06-11-2003, 04:45 PM

Ok - so at least I know it should not 100% cut off. So where is the resistor pack and how would one diagnose that?

jbaj007 · #6 06-11-2003, 04:50 PM

If, during the "cool down" cycle, all fan speeds are available and working when you push high, low and auto buttons, it would seem that the fan is fine, but that a signal from the climate control unit is at fault when you reach the set temperature. Since you reported in a previous thread that you had done some "definitive" tugging in the area of the climate control unit, perhaps one of the connector blocks on the sides of said unit have been tweaked loose?

bodyart27 · #7 06-11-2003, 05:09 PM

I'm trying to find the tool to pull the sereo so I can remove the wood panel with the A/C controls (hopefully my parents didn't throw it away - it's their old car). Hopefully just a loose wire.... I'll let you know if I can get the panel off. Thanks for the input!

bodyart27 · #8 06-12-2003, 11:57 AM

I had to order the removal tool for this blaupunkt (sp?) stereo - it's coming from Germany and it's going to take 4-6 weeks.

Good news is with shipping it's only $13.

Ugh - I guess I'll deal with this funky cycling for a month or so!

sixto · #9 06-12-2003, 04:02 PM

A car stereo shop probably has tools you can borrow or rent.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD