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  #1  
Old 12-09-2020, 02:11 PM
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Location: Houston, Texas
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Red face 300SDL Climate Control Clicking When Cold Outside Temperature

Well I’ve done a search and can’t find the exact solution to my problem.
The car is 1987 300SDL.

Symptoms:

Outside temperatures colder than 50 degrees.
Activate automatic temperature by pressing the EC button next to the O (Off) button. Temperature dial set at 22.
Almost immediately I start hearing clicking behind the dash.
The recirculating button light comes on and off each time it clicks.
If I push the high button the fan turns off and on, follow the click like there’s power to the fan then nothing then power again to the fan and then nothing. It clicks at all fan settings.
Eventually the entire system quits working. No fan; nothing. It reverts to default mode by opening the heater full and heated air coming through the center vents while driving with ram air.....gets pretty hot inside.
When outside temperature outside is mild like 70 degrees the entire system works fine!
The fuse at fuse box is fine; I even replaced it thinking it was the problem but no change. It still has same symptoms when it gets cold outside and the car is cold soaked.
I found a tread of similar problem but when they tried replacing the climate control unit it didn’t help them. I would like a more definitive way to diagnose before I buy a new CCU to make sure. Maybe it’s something else.

Suggestions? Your help would be most appreciated!

Thanks!

Herb

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  #2  
Old 12-09-2020, 02:54 PM
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Unplug the auxiliary coolant pump (plug is in a holder down next to the battery) and see if your behavior changes. The pumps are known to seize and cause all sorts of problems. The heat should work just fine without it.
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  #3  
Old 12-09-2020, 03:39 PM
Grom
 
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Location: San Diego, CA
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Another possibility: the 'cold air lockout' sensor on my W123 had frayed wires and creating a clicking sound on the push button unit. I ended up just grounding it and it went away, it's not a feature I need.

Not sure if your car has one as well, but mine is on the thermostat housing.
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  #4  
Old 12-09-2020, 03:46 PM
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Quote:
Originally Posted by imgolden View Post
Another possibility: the 'cold air lockout' sensor on my W123 had frayed wires and creating a clicking sound on the push button unit. I ended up just grounding it and it went away, it's not a feature I need.

Not sure if your car has one as well, but mine is on the thermostat housing.
The Gen II W126 and W124 system is entirely different from the W123 and Gen I W126 system.
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  #5  
Old 12-10-2020, 02:07 PM
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Quote:
Originally Posted by Diseasel300 View Post
Unplug the auxiliary coolant pump (plug is in a holder down next to the battery) and see if your behavior changes. The pumps are known to seize and cause all sorts of problems. The heat should work just fine without it.
Hi. Is this the plug? I’ve marked it with a small screwdriver.

Thanks!

Herb
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300SDL Climate Control Clicking When Cold Outside Temperature-0b11e5c4-dcfc-4a36-8652-73cff0d90fe0.jpeg  
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  #6  
Old 12-10-2020, 02:24 PM
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Quote:
Originally Posted by airfoill View Post
Hi. Is this the plug? I’ve marked it with a small screwdriver.

Thanks!

Herb
Yes, that's the one.
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  #7  
Old 12-10-2020, 02:40 PM
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Quote:
Originally Posted by Diseasel300 View Post
Yes, that's the one.
Thank you. I just now unplugged it. I’ll see what happens next when it gets cold around here in Texas.
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  #8  
Old 12-10-2020, 07:18 PM
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cold/cracked solder joints?

When electronics act up due to significant temperature differentials especially given a 33 year service life, I would suspect hairline fractures in the solder joints on the Climate control unit. Given its age, it would be time well spent to reflow the solder on any pins you can access. This also usually fixes many switch button related issues.

There are also some capacitors worth changing, I dont recall the specifics but it is well documented on the forum. If you need a few, PM me, when I did mine I had to purchase a 20 pack, so can spare a few.

Good luck
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  #9  
Old 12-14-2020, 10:48 PM
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Quote:
Originally Posted by 87tdwagen View Post
When electronics act up due to significant temperature differentials especially given a 33 year service life, I would suspect hairline fractures in the solder joints on the Climate control unit. Given its age, it would be time well spent to reflow the solder on any pins you can access. This also usually fixes many switch button related issues.

There are also some capacitors worth changing, I dont recall the specifics but it is well documented on the forum. If you need a few, PM me, when I did mine I had to purchase a 20 pack, so can spare a few.

Good luck
It was relatively cool here in Houston today..around 50 or so. Started up the car and with the auxiliary pump disconnected, it the CCU clicks with the blower fan coming on and off. The recirculating button light also follows the clicks. So it appears that isn't the problem.

Well I wanted to check the easy stuff first and verified the auxiliary pump works because I jumped leads to power it and i hear a humming noise so i believe it works. However I did keep it unplugged it as recommended by another post. I know the monovalve works because when the car is in mild weather it does regulate the heat as needed....however could a monovalve that appears to be working also be the problem?

Now as to reflowing the solder. I've never done anything like that before and was checking to see how difficult it would be. I have zero experience with electronics and feel that I may make things worse by reflowing and ruin the CCU. Is there someone that does this on the forum or has step by step tips on how to do this?

Thanks for the help

Herb
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  #10  
Old 12-15-2020, 01:56 PM
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You could have a bad ground issue too. Cold weather tends to exacerbate poor connection issues. Do you hear the aspirator fan whirring during cold weather? If the key is on, it should be making noise behind the glovebox. Tried spinning or replacing Fuse #5 in the fuse box? It powers the CCU. The CCU board in the Gen II's doesn't have relays on it, so the clicking is something else, likely the solenoids for the mixing doors or something else in the dash.

Have you tried running the system with the center button pressed? It should still heat in that mode. If it works normally in that mode, but not in "EC", it's likely a broken solder trace or a bad switch.

I believe Kris Rose (JamesDean) rebuilds these boards. I've also rebuilt several for myself and various other folks I know. There's not a lot to go wrong in them, but when they do have a problem it's usually pretty obvious if you know what you're looking for.
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  #11  
Old 12-21-2020, 10:50 AM
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Well I removed the front panel where the CCU sits and part of the left side passenger panel. Turned on the car when it was cold outside and found that the clicking sound is coming from the vertical vacuum switching solenoid mechanism sitting next to the CCU that controls the vacuum to specific doors; there is no clicking at all from the CCU itself. Im including a picture.

I did an additional experiment by disconnecting the mono valve plug and the clicking at the vertical switching solenoid still exists.

Pressing the three buttons to the left of the CCU appears to stop the clicking; although as the temperature was starting to get warmer it appeared to fix itself. Once everything is warmed up everything works like it’s supposed to.

After this experiment I took out the CCU and opened up the bottom and looked at the soldering on the big mother board by inspecting the solder. I used a magnifying glass and could not see anything wrong by way of cracks as suggested. There was no evidence of burning or anything like that. Like I have said before I’m not an expert in electronics and I know if I tried applying a soldering pen each of those points I’d probably have a mess and probably ruin a perfectly good unit. I’m leaning to buying another CCU or paying someone to resolder my unit. From what I’m describing, does it appear to be the CCU itself?

If I order a replacement CCU I’ve looked on the forum and it is important to order the correct CCU part because of some subtleties. When I took the CCU out, there is no part number anywhere that I can see printed on the unit. How do I find the correct part number on this unit?

Thanks for the help

Herb
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300SDL Climate Control Clicking When Cold Outside Temperature-29cfd763-0555-4173-a10d-aa3d36525bcb.jpeg  
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  #12  
Old 12-21-2020, 03:17 PM
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The solenoid block is a *VERY* common source of problems on W124 and gen II W126 cars. The printed circuit board inside is a cheap design and the solenoids routinely break free and cause all sorts of intermittent issues. It's repairable, but you have to take a knife or saw and cut the case apart.

Given that you're having multiple problems, my suspicion would be a bad ground that's common to the various functions you're having issues with. Bad grounds are common in these cars and cold weather/moisture exacerbate them.
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  #13  
Old 12-21-2020, 04:05 PM
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Quote:
Originally Posted by Diseasel300 View Post
The solenoid block is a *VERY* common source of problems on W124 and gen II W126 cars. The printed circuit board inside is a cheap design and the solenoids routinely break free and cause all sorts of intermittent issues. It's repairable, but you have to take a knife or saw and cut the case apart.

Given that you're having multiple problems, my suspicion would be a bad ground that's common to the various functions you're having issues with. Bad grounds are common in these cars and cold weather/moisture exacerbate them.
Where would be a good place to start regarding a bad ground....most likely places to look.

Thanks
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  #14  
Old 01-09-2021, 01:05 PM
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Problem Solved

Well I found the problem. After looking for grounding issues which is next to impossible because the connections are buried under dash, I decided to try a couple of experiments and recreate the conditions that exhibited my problem of no climate control when outside temperatures were cold. I removed the CCU and placed it in the sun on the rear shelve where the speakers are and let it sit there for about 30 minutes to get it nice and warm. Then I immediately took the CCU and plugged in both connectors and started the car. The CCU operated flawlessly. I then unplugged the CCU and placed it inside a refrigerator freezer for about the same time of 30 minutes and then took it out and plugged both connectors back to the CCU and started the car......no nothing!! So it appeared the CCU was defective and I ordered a new one. The new one works flawlessly like it should. Removing the CCU wasn’t difficult at all but you do have to follow a sequence or you will end up breaking the wood.

I am still leaving the auxiliary pump unplugged because I’ve read here that you really don’t need it anyway and my heater works fine without it. If the auxiliary pump fails I’ve heard from this forum that the CCU can get damaged. I’m doing this as a preventative measure to mitigate risk in case the auxiliary pump ever shorts out.

Another concern is the mono valve. Mine is working normally. Again I’ve read on this forum that if the mono valve shorts out it may also damage the CCU. So my question is two fold. Do you guys preemptively replace the solenoid mono valve just to play it safe with the CCU as preventative maintenance? Also the quality of the mono valves are supposedly not the same quality as before. Where do you guys get good quality mono valves?

Thanks

Herb

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