Climate Control Problem - PeachParts Mercedes-Benz Forum

spyguy · #1 05-25-2006, 11:44 AM

I'm getting ready to put a new compressor in my 85 300D. The old one was completely dead and didn't even have a belt on it. I'm concerned that I may have other issues with the vents and air distribution. Currently the fan seems to work, high, low, and changes speed in the auto position. Air distribution does not seem right. Air always blows at the wind shield, never from the center 2 vents, always at the side vents. When I turn the temp wheel to heat I get plenty of heat but it takes a long time for it to stop heating once I move the wheel to the cool position. I recently got this car so I don't know when it stopped working right. Where do I start? I'm not totally clear what each of the buttons actually does either. Thank you.

300sdToronto · #2 05-25-2006, 11:55 AM

I have a 126 chassis and am no expert on the differences, but a new monovalve cured several weird problems on my 300sd with erratic climate control behaviour.

Took about 10 mins to replace, including finding it, which was the hardest part.

TX76513 · #3 05-25-2006, 11:59 AM

This is probably the best place to start http://www.peachparts.com/Wikka/AcDiags Steve's DIY that has helped so many.

300sdToronto · #4 05-25-2006, 11:59 AM

1. once you replaced the monovalve, set the temperature control dial to a cool temperature, select auto fan and the economy setting (second button on the right). take the car for a drive - the system should try and cool the cabin using the dash vents. air will of course be at ambient temp.

2. if no joy in 1 search the forum for climate control. You will find an excess of hits. happy reading.

3. solicit help from those more expert than me (another newbie)

spyguy · #5 05-25-2006, 03:23 PM

Are there any good links on troubleshooting these systems...or some good schematics? Also, how do I get a look at the swiches and pods? Pull apart the dash, glove box or what? Someone had told me to get a Mityvac for testing but I need to know how to do the testing.

TX76513 · #6 05-25-2006, 03:31 PM

Click on the DIY Articles and DIY Links tab on the top of the screen, probably two months worth of reading there

spyguy · #7 05-25-2006, 11:33 PM

I just picked up a Mityvac at Autozone so though I'm not quite sure how to find all the vac components I'll pull off some panels and glove box and try to get started.

SD Blue · #8 05-26-2006, 12:12 PM

You may be getting the cart before the horse.

Quote:

Originally Posted by spyguy

I'm getting ready to put a new compressor in my 85 300D. The old one was completely dead and didn't even have a belt on it. I'm concerned that I may have other issues with the vents and air distribution. Currently the fan seems to work, high, low, and changes speed in the auto position. Air distribution does not seem right. Air always blows at the wind shield, never from the center 2 vents, always at the side vents. When I turn the temp wheel to heat I get plenty of heat but it takes a long time for it to stop heating once I move the wheel to the cool position. I recently got this car so I don't know when it stopped working right. Where do I start? I'm not totally clear what each of the buttons actually does either. Thank you.

Spyguy,
Before you shell out cash for a new compressor, ensure that everything else is up to snuff. Are you getting 12v at the clutch when you select the A/C mode? (#3 from the right and max. cool on temp.) If not, the power comes through the ACC controller and it may have a solder joint that needs touching up. (BTDT)

Touching up those solder joints, on the board edge connections, may also cure the vent problems. Try that first and we can go from there.

Cateaux · #9 05-26-2006, 02:46 PM

Quote:

Originally Posted by spyguy

I'm getting ready to put a new compressor in my 85 300D. The old one was completely dead and didn't even have a belt on it.

If the compressor is locked up, I guarantee that you have debris choking the entire system. If you're lucky you can flush the system out and you won't have to replace anything else but the accumulator. Condensors are sometimes so clogged that they can't be cleaned. You also may have leaks. Is the system currently holding a charge?

Quote:

Originally Posted by spyguy

Air always blows at the wind shield, never from the center 2 vents, always at the side vents....Where do I start?

Air is always supposed to blow from the side vents. When no (or not enough) vacuum is present, the vents will default to defroster-open and center vents-closed. A vacuum leak anywhere can affect any vacuum-driven component on the car. Start at the main vacuum line that goes from the vacuum pump to the brake booster, which should draw about 17Hg while running, IIRC. Then work your way to whatever doesn't hold vacuum. You'll have to do alot of reading to understand how the vacuum system works, but once you understand it it's not too hard to troubleshoot.

spyguy · #10 05-27-2006, 01:08 AM

After a bit of testing in various spots it looks like I have vacuum. All the pods seem to be working except maybe the one that runs the center vents. Not sure what to do next about that. I did take the controller out and did all the solders on it. Now I hear a click or two when the the ignition is switched on and thankfully the defroster blows at the windshield and the heater down at the bottom-temp goes up and down with the setting. Off shuts down everything. I have not yet tried to see if I get 12V at the compressor when button 3 is pushed. As I was observing the pod behind the glove box.(The one way up and in toward the firewall.) I noticed that it seemed to pull in then "relaxed" out. Is this normal? I'm waiting for my Freeze 12 and the special oil that Diesel Giant recommends before I install the compressor. In the meantime I used AC flush and compressed air to clean things out. Hopefully it will hold vacuum once I'm at that stage.

SD Blue · #11 05-27-2006, 10:25 AM

For center pod repair here is a write up, with some details, for when I changed mine.300SD Climate Control

For the fresh/recirc,are you applying vacuum at the pod itself? If so, then it sounds like it is definitely leaking. I have read that the long-travel pods, such as this, have to be replaced with new/salvage.

Source for replacement diaphragms: www.autoluxmb.com

Cateaux · #12 05-27-2006, 12:31 PM

Quote:

Originally Posted by spyguy

As I was observing the pod behind the glove box.(The one way up and in toward the firewall.) I noticed that it seemed to pull in then "relaxed" out. Is this normal?

I'm not sure which pod you are referring to. The one near the firewall to the right of the glovebox controls either fresh air or recirculating air; I don't recall which. The pod to the left of the glovebox controls the center vents. I have this one disconnected on my car. I disconnected the arm from the door underneath the center vents and left it in the open position. If I don't want air from the center vents, I close them manually like the side vents. To replace it I would have had to take the dash out. Some have been able to change it with the dash in but my hands are just too big. Whichever it is, it should hold vacuum until you release it. If it relaxes out it needs to be rebuilt/replaced/disconnected.