Climate Control Headaches

[lietuviai]

OK, I've been having issues with the heater on the CC. It seems to work when it feels like it. The defroster works fine but is too much to just use as a heater. It seems the temp wheel may be part of the problem because if it is set to anything but the coldest max setting, the defroster will not blow. OTH the other vent settings will sometimes work with repeated coaxing (switching between the defrost button and and another button) when the temp wheel set to something warmer. Usually all that happens is that the various relays can be heard clicking from inside the dash and vents operating. I've checked the ccu itself and all the solder joints look fine. I've also checked all the connections to every locatable component of the heating system and they were fine.
An added note, the A/C system lost it's charge a few years ago but that didn't affect the heater from functioning then. I think I've checked everything but there is something that is eluding me.
Any ideas where to go or what to check specifically? I don't have another CCU to check against the one I have.

[tangofox007]

Originally Posted by lietuviai

It seems the temp wheel may be part of the problem because if it is set to anything but the coldest max setting, the defroster will not blow.

By design, the temperature selector is nonfunctional in the Defrost mode. In Defrost, you should get maximum heat and maximum fan speed, regardless of the temp selector position.

Originally Posted by lietuviai

I've been having issues with the heater on the CC. It seems to work when it feels like it.

That is consistent with cracked solder joints and/or dirty relay contacts in the push button unit.

[lietuviai]

I'll look at the solder joints and check the relays again. It's possible a joint or two may have cracked after pushing the buttons with my fist a few days ago.
Oddly it was working sporadically on my trip into town today.
The strange thing is, the defrost will not work or quit working if the temp wheel turned away from the max cool setting.

[Tanksowner]

Hey man

If all you need is heat, disconnect the aux water pump and monovalve. Whunter told me a while back that if there's even the smallest tear in the monovalve diaphragm, it'll wreak havoc with the whole system. With both of these disconnected, you'll at least have heat until warmer weather sets in. Without a doubt, any ACC system on an old Benz is incredibly complicated and to truly find the problem (chances are there's multiple ones) could take days. I don't even mess around with it; I give it to my mechanic who's an air conditioning/climate control specialist. He had a W123 many years ago and said the Achilles heel to such a fantastic car was the climate control. I now understand why so many of the guys on here say convert to a manual system!

[tangofox007]

Originally Posted by Tanksowner

Hey man

If all you need is heat, disconnect the aux water pump and monovalve. Whunter told me a while back that if there's even the smallest tear in the monovalve diaphragm, it'll wreak havoc with the whole system.

Unfortunately, the problems associated with a torn monovalve diaphragm are mechanical in nature and are not necessarily subject to an electrical solution. Furthermore, claims of "wreaking havoc" with the "whole system" are greatly exaggerated; nothing is affected but coolant flow through the heater core.

[Tanksowner]

Originally Posted by tangofox007

Unfortunately, the problems associated with a torn monovalve diaphragm are mechanical in nature and are not necessarily subject to an electrical solution. Furthermore, claims of "wreaking havoc" with the "whole system" are greatly exaggerated; nothing is affected but coolant flow through the heater core.

That's a good point. I didn't think of that. Perhaps hooking up a voltmeter to different relays related to the system will yield some further insight?

[lietuviai]

I think I fixed the CCU. I resoldered every joint that looked questionable plus every joint that can crack on the main board to the side boards and every relay pin. Plus I recrimped every plug on the temp wheel and fan switch controllers. The fan will blow on most if not all vent selections and at all speeds including the automatic speed switch.
The CCU itself appears very crude and even poorly designed. The side boards need more reinforcement since unplugging it could apply stress on the solder joints and break them. It should have been made more like the cruise control box, with an aluminum housing.
I regret not converting the system to manual when I had my 240D manual transmission donor car. It would have been a good swap to attempt.
While I had the car in the garage, I also replaced the rear brake pads. That was really the main reason why I was working on it today.
Thanks for all the suggestions guys.