Clicking CCU - PeachParts Mercedes-Benz Forum

lietuviai · #1 09-04-2009, 10:26 PM

Yesterday my CCU started clicking while it was on. It was frequent. It didn't matter what speed the fan was set to. At first I thought it was because it was set on the "Auto" speed but switching to high or low didn't make a difference nor did switching to different setting. The CCU has had a habit of just switching off in the past, mainly on the two upper vent settings.
Is this a sign the CCU is calling it quits or are there some terminals that just need some resoldering as mentioned in a recent thread?

babymog · #2 09-04-2009, 10:56 PM

Checked your aux. pump lately? I don't know if this is a problem in the 123s, just throwing it out there anyway.

lietuviai · #3 09-04-2009, 11:01 PM

I haven't looked at the pump yet. They are known to freeze up and fry the CCU's on the 123's too. Thanks for reminding me about that one.

Jeremy5848 · #4 09-05-2009, 12:15 AM

The clicking is coming from one of the relays that live in the CCU. Sorry that I don't have a clue as to why the clicking is happening.

RML · #5 09-05-2009, 10:12 AM

I agree that it is most likely one of the relays. They are the only things in there that I can think of that would click. So there is a signal coming in that is tripping it open and shut. Or maybe there is some dirt or corrosion that is interfereing with a signal. You might try taking it out and blowing off the board and relays with compressed air. That would eliminate one variable.

lietuviai · #6 09-05-2009, 11:41 AM

Clicking sounds from the relays make sense. I'll have to check to see if there's any burnt or pitted contacts at the same time. The thing that puzzles me is that there must be some errant signal in the circuit to be causing it. I'll probably also have to check the fan and the resistor for any bad connections as well.

lietuviai · #7 09-06-2009, 12:36 AM

I opened up the CCU and I didn't find anything that looked bad. The relays had no burning or pitting. The usual cracked soldered terminal were fine. The only thing I can figure at the moment is maybe the switches themselves have some bad connections internally but there doesn't appear to be a way to take them apart short of desoldering them from the boards and that's not going to happen.
There's mention of a blower regulator in a recent thread. Perhaps my problems are originating in that mysterious little black box?

lietuviai · #8 09-07-2009, 11:52 PM

I checked the aux pump and it works fine. I also located the fan relay but I didn't bother taking it out as I figured there probably isn't anything I could check inside it anyway. However I did check the connection and even pried off the connector to make sure it was making a good connection.
Has anyone ever opened on up to see what's inside and if there's anything that is serviceable or what to look out for that could be burnt, etc.?

funola · #9 10-03-2009, 09:03 AM

I had a lot of clicking noise from the CCU in my 300D. I took apart the temp dial. Inside was a variable resistor (potentionmeter). I cleaned it with brake cleaner and put it back together and NO MORE CLICKING for me. YMMV.

lietuviai · #10 10-03-2009, 11:45 AM

That's a good tip. I would have never thought about the temp wheel.
I'm not pursuing any more CCU repairs though. My A/C system sprung another leak somewhere so I'm done throwing anymore money at its POS HVAC system.

funola · #11 10-06-2009, 06:54 PM

Quote:

Originally Posted by lietuviai

That's a good tip. I would have never thought about the temp wheel.
I'm not pursuing any more CCU repairs though. My A/C system sprung another leak somewhere so I'm done throwing anymore money at its POS HVAC system.

How about convert it to a manual system? I have all the parts you need from my 240D parts car.

lietuviai · #12 10-06-2009, 08:03 PM

I thought about doing that originally while I still had my 240D parts car but I didn't have the time to do it. I would still have to buy all new hoses and that would be prohibitively expensive for me at the moment. I'm looking at about $600-$750 in hoses alone. I might need a new compressor, condenser and possibly even an evaporator.
If you don't mind though, what are you asking for your parts?

funola · #13 10-06-2009, 08:34 PM

What's a fair price? The 4 spd manual transmission, drive shaft, shifter, clutch pedal, clutch master and slave cyl has been sold. Everything else is available.

lietuviai · #14 10-06-2009, 08:37 PM

Honestly I wouldn't know what the fair price would be other than what a PnP would charge.

funola · #15 10-06-2009, 08:51 PM

What would PnP charge? We don't have no PnP's here so I'm curious.