A.C. troubleshooting guide? - PeachParts Mercedes-Benz Forum

showme · #1 06-14-2010, 03:57 PM

I'm getting ready to figure out what's wrong and what's right with the 81 300D's AC. Is there a recommended troubleshooting list that I could use to check off possible problems in order to keep from going to a shop and paying out the wazoo for a possible simple fix? I wrote a post last week about how my wife's ac is not kicking on correctly. Mainly, the blower seems to be the problem, (kicking on randomly, but mostly not), but now that I'm retired and have lots of time on my hands, I'd like to learn how to do this myself, and understand what's going on and why. (I envy your knowledge, all you AC guys.) Lee

TX76513 · #2 06-14-2010, 04:06 PM

This LINK http://www.classictechlit.mbusa.com/MB/ is to MBUSA Techinal Data and the W123 FSM (service Manual). It this FSM is like the W126 it will have the CCU Trouble shooting manual which is priceless for doing the 1 - 2 - 3 in tracing down your problem. Much better than throwing parts at it.
I am fairly sure its included in the W123, but someone will chime in and validate that statement.

showme · #3 06-14-2010, 04:31 PM

Went to the link and found my model, but it doesn't give much info on what i'm ordering. You say this is a pretty detailed manual? Sounds like a good deal if it has a lot of info, especially on the AC problem. Can it be ordered in paper or CD, or is it just CD? THanks for the lead and any answers to the above questions. (Do you know your avatar?)

Whiskeydan · #4 06-14-2010, 06:03 PM

Have you wiggled the key in the "on" position to see if the blower starts working. An inop blower seems to be the first thing you'll notice when the ignition switch is worn.

Check the blower motor's fuse and it's holder for damage also. If the fuse holder is melted then your blower motor most likely needs attention as it is drawing too much current.

showme · #5 06-14-2010, 08:27 PM

I replaced the ignition switch earlier this year, cause the old one was shot. It's a new switch, but i'll still try it. I haven't gotten in and looked at any fuses yet, but I've heard that one quite a few times. And my daughter had a 240D that had its holder fried when she got it. She sold it before I got it fixed, but I've read all about (and seen) what a bad blower circuit can do. Thanks for the advice. Unless is storms tomorrow, I'll be out in and under the car at daybreak. (Well, maybe not daybreak) thanks again!

RickR1983 · #6 06-14-2010, 11:48 PM

Tracing electric continuity solved my problem. I was having the same on/off problem and found the problem was the control head (the thing with all the buttons on it for the vent, a/c, etc.). First I tried to resolder what I thought were the bad connections, it worked better through the end of last summer. However, I invested in the new control unit in the late spring for this summer. Not very hard to put in and it did the trick. Hope this helps. In Phoenix, A/C is a gotta have in the summer.

showme · #7 06-15-2010, 09:40 AM

That's good news. I have a brand new control head sitting in my tool room that I bought just in case. Actually, I thought I'd go ahead and put it in first and hope for the best. I've wondered if I may have messed something up when I was fooling with the console\dash when I got into it to change my stereo a few months back. (The same time I broke the bezel on my window switch, of which I've now installed a new one. [Works great!]) I'm getting ready to get out there and change my water pump and belt, and my oil and fuel filters, plus a few other things that should be great fun on a humid, 85* day.

Thanks for your input! I still am going to learn to troubleshoot the complete system. I want to know how these things work!