300 SD - 1982 Climate Control Driving Me Crazy - PeachParts Mercedes-Benz Forum

nyko46 · #1 12-09-2009, 05:27 PM

After many searches about troubleshooting my Climate Control, I decided to remove it from my car and check all soldering pints, traces, push buttons, and also perform a general clean up in the unit.
I found one trace interrupted and had it fixed properly. After that I checked with my meter, continuity in all traces and connections but nothing more was found wrong. As it was opened on my bench I took the opportunity to clean all relays and push buttons with an electronic contact cleaner.
Then I install it in my car and it still not working. When I say "not working" it means that nothing is working in the unit. The first check done was on my blower and it work when applying 12 V directly to it but not when pushing any button in the ACC. I spent all my day in a cold weather to get it running but I still asking "What could be wrong with it ? "
I found a good link about repair this unit and I was hoping to get it working fine after finished all repairs and installing in the car but the problem still.
Any suggestion will be appreciated.
Thanks

leathermang · #2 12-09-2009, 05:36 PM

Have you checked to see that you have really good vacuum to the unit ?

nyko46 · #3 12-09-2009, 05:39 PM

Quote:

Originally Posted by leathermang

Have you checked to see that you have really good vacuum to the unit ?

No, I did not check for vacuum.
Where is the vaccum line suppost be?

Brian Carlton · #4 12-09-2009, 05:58 PM

Quote:

Originally Posted by nyko46

No, I did not check for vacuum.
Where is the vaccum line suppost be?

There is no vacuum to the unit. It provides electrical control to the vacuum valves that operate the pods.

You can screw around with that unit until you've wasted 50 hours and then you'll go and get a rebuilt unit. Or, you can save the 50 hours and do it right now.

Your choice.

There is no definitive plan to repair those units by any of the folks on the forum. It's strictly a hit or miss approach with a soldering gun...........and I can tell you from experience that "miss" is far more likely. Even if you do manage to get it running, it'll be failing again within one year.

leathermang · #5 12-09-2009, 06:01 PM

If it is sending signals to vacuum pods which are not getting vacuum wouldn't that show up as not working ?

engatwork · #6 12-09-2009, 06:37 PM

How do you know it is the pushbutton unit? What troubleshooting procedures have you used?

Brian Carlton · #7 12-09-2009, 06:39 PM

He made no mention of any specific vent that was not functioning...........the only symptom stated was the inability for the CCU to operate the blower.

Be tough to make a vacuum problem out of that.

nyko46 · #8 12-10-2009, 03:38 PM

About absence of vacuum, I have read in the Mercedes Benz repair manual that the windshield defrost should work with engine not even running if the ignition key in ON position. In my specific case none of the selected push buttons will work with or without engine running.
I can fell hot air coming from vents with the car in movement at 50 or more miles per hour but it is the air forced into the car due the speed.
About the questioned "how did I troubleshoot the push buttons" it was made based on my experience in troubleshooting CNC machine that has many components including push buttons that operates with low voltage from 5 V to 24 V DC and in low voltage small oiled or dirty is enough to make contacts to block the flow of current to the next part of the circuit. I did it using my ohm meter and after all contacts checked I clean it with an electronic contact cleaner. It works smooth now than before but did not help the CCU to get running.
I had questioned myself about those two boxes attached to blower case when looking from underneath that is also part of the CCU. Can those parts have some interference with blower, vent pods, etc.?
Before the CCU stop run when switching vents it was possible to hear those pods also changing but now everything stop work. The only thing NOT YET checked was the vacuum lines but based in the information that windshield defrost should work with engine not running, I assume that not vacuum is required at least for that function.
I would like to hear more from members of this forum before go ahead and buy another unit and maybe the problem is in somewhere other than the unit itself. I appreciate all comments from everyone.

Brian Carlton · #9 12-10-2009, 03:43 PM

Quote:

Originally Posted by nyko46

I would like to hear more from members of this forum before go ahead and buy another unit and maybe the problem is in somewhere other than the unit itself. I appreciate all comments from everyone.

If the blower works when 12V is applied, but won't work when the CCU is controlling it, the problem is the CCU or the blower controller. I don't know how to determine which of those two is the culprit, however, in my specific case, I rolled the dice with the CCU and was correct.

nyko46 · #10 12-10-2009, 03:54 PM

Quote:

Originally Posted by Brian Carlton

If the blower works when 12V is applied, but won't work when the CCU is controlling it, the problem is the CCU or the blower controller. I don't know how to determine which of those two is the culprit, however, in my specific case, I rolled the dice with the CCU and was correct.

Brian:
When you say "blower controller" are you talking about those three push buttons vertically aligned at the right hand of the CCU?
Thanks.

Brian Carlton · #11 12-10-2009, 03:56 PM

Quote:

Originally Posted by nyko46

Brian:
When you say "blower controller" are you talking about those three push buttons vertically aligned at the right hand of the CCU?
Thanks.

Negative.

The blower controller is a "black box" that provides the sequencing for the resistors and gives the blower the six discrete speeds. I believe it lives behind the dash on the passenger side.

nyko46 · #12 12-10-2009, 04:02 PM

Quote:

Originally Posted by Brian Carlton

Negative.

The blower controller is a "black box" that provides the sequencing for the resistors and gives the blower the six discrete speeds. I believe it lives behind the dash on the passenger side.

Thanks for the update.
Those resistors are located inside of this black box or in another place?
Thanks again.

Phil · #13 12-10-2009, 04:36 PM

Just to make sure, do you have power to the ccu and if so do you get power to the input to the blower controller?

nyko46 · #14 12-10-2009, 04:55 PM

Quote:

Originally Posted by Phil

Just to make sure, do you have power to the ccu and if so do you get power to the input to the blower controller?

The first thing that I did was to check all fuses on the fuse box and they are all good. I don't know exactly where to check power to the ccu on it's female connector and also where to check power in the blower controller.
I did check for power in the connector for blower as mentioned before but there are no power when ccu and defrost is on.
Please send me some more idea because they are valuable.
Thanks

Brian Carlton · #15 12-10-2009, 05:49 PM

Quote:

Originally Posted by nyko46

Thanks for the update.
Those resistors are located inside of this black box or in another place?
Thanks again.

The resistors are located in another place............between the two firewalls on the driver's side...........and sensitive to any accumulated leaves that will catch on fire if they happen to contact the resistor coils.