Climate control trouble, 1983 300sd - PeachParts Mercedes-Benz Forum

greaser · #1 09-01-2009, 09:56 AM

The heat works in warm weather, but not cold. I hear the fan go on occasionally at random times and paddles opening and closing at random times under the dash. I would like to wire the whole thing to run manually. Anybody ever try this. All I hear are bad stories about this system.

Thanks for any replies.

Ted

I also think there are lots of threads about this and if anybody knew of any I'd be greatful for showing them to me. I just can't find any.

John Schroader · #2 09-01-2009, 11:08 AM

Computer doofus that I am, I don't know how to give you the link. So here's the old fashion way to read about repairing the CC. Go to the DIY section of this site. Click on climate control. Click on CC repair by BoostnBenz on 2/16/04. I used this advice to repair mine. Good info.

John Schroader · #3 09-01-2009, 11:26 AM

http://www.peachparts.com/Wikka/W123ClimateControl That's the site. Wow!!!!! Am I now in the 21st century.

micalk · #4 09-01-2009, 04:07 PM

Don't repair it till you isolate your problems to it. Have you tried following the troubleshooting procedures/tests in the service manual? If you pull the plug on the ACC Amplifier (I believe that's what it is called - it's a module on the passenger side in the blower motor area) almost all the tests can be run with only a volt-ohmmeter. The tests will rule out sensors, wiring, switches, much of which may come into play even with a manual system. You could have a bad cabin temp sensor or water temp sensor. If you rule all those other things out and isolate your problem to the ACC control unit, then you might resolder or consider going manual. But you're not going to want to go through all that trouble only to find out your problems are in some other part of the system that you'll need to repair anyway.

When I bought my car almost a year ago, the a/c didn't blow very cold, and with the heat on the fan would cycle up to full and blow full heat even with the temp wheel all the way down. Bad monovalve. Repaired that and the whole system has been working wonderfully ever since. For all its supposed faults, when it's right it's a thing of beauty.

1lowdiesel · #5 09-01-2009, 04:42 PM

i was having some funky issues with mine and decided to just replace the whole switch assembly. everything works 100% now.

well 90% once i charge my A/C we'll be at 100%

cousindave76 · #6 09-03-2009, 11:13 AM

I've got some funky problems with mine too. The temp wheel works fine but, sometimes the system will just completely shut down. It's stays off for a while then suddenly comes back to life. I have figured out that when it shuts down, I can switch the fan to FULL and press the defrost button. It starts to blow strong immediately. After waiting a minute or two the cold air from the defrost vent will start blowing heat. Once the heat starts coming through the vents I can switch it back over to normal A/C, the air blows through the forward vent again and it's cold, and it works fine again. You guys know what would cause that? Monovalve? Control unit?

Micalk, any links to information on all those test to run? My service manual does not outline such testing. It just tells me that it's to complicated for me to understand and to send it to the dealer... how dare they assume that!

I have a nice multimeter and would love to test everything out.

toomany MBZ · #7 09-03-2009, 12:32 PM

Common problems, pull the unit and check for cold solders.

John Schroader · #8 09-03-2009, 02:44 PM

My wife's 83 SD does some wierd stuff along those line also, but we have learned how to live with it. Will fix it soon as I fix a few other things that are harder to live with.

cousindave76 · #9 09-03-2009, 03:50 PM

Quote:

Originally Posted by toomany MBZ

Common problems, pull the unit and check for cold solders.

So if I pull the control unit, will the problem solder areas be apparent? Broken, loose? Or are there spots that should be resoldered wether a problem can be seen on not?

Thanks Mr MBZ!

cousindave76 · #10 09-03-2009, 04:01 PM

Of course only after asking the question do I finally find the writeup. This link has a terrific step by step guide.

http://w123maintenance.blogspot.com/2007/10/automatic-climate-control-unit-repair.html

Thanks!

toomany MBZ · #11 09-03-2009, 07:35 PM

Yeah, that's a bit more involved, pop off the panel, those pins soldered to the board will sometimes vibrate loose, you'll see a hairline crack surrounding the pin. Re-flow the solder adding any if necessary.

1lowdiesel · #12 09-03-2009, 08:49 PM

when i pulled my stock one out you could see alot of brown spots (burt areas) on the board under the panel.

unfortunatly for me someone was already in there and tried their own hokey repair. so i was stuck with just getting a new control unit.

if you need a new one you can actually use one from a non sd as well. i got mine out of an 82 300cd

cousindave76 · #13 09-03-2009, 09:30 PM

I'm pretty sure my unit probably has not been repaired before. I've been driving this car for about 5 years now and only in the last few months have started getting this problem. So I hope when I pull it I will see the problem with the solder as described and be able to repair it. Fingers crossed!

micalk · #14 09-04-2009, 09:19 AM

Quote:

Originally Posted by 1lowdiesel

if you need a new one you can actually use one from a non sd as well. i got mine out of an 82 300cd

The 126 ACC controls six changeover valves / vacuum pods vice five for the 123. Another unit may "work", but it may not be fully functional. Check part numbers to be sure.

cousindave76 · #15 09-04-2009, 11:24 AM

I actually do have a 126. Though not the same, the diy fix seems pretty universal. If for any reason I have to replace it, I'll be sure to get the right part.

Thanks!