No heat or too much heat, monovalve or CCU? - PeachParts Mercedes-Benz Forum

muleears · #1 11-14-2012, 08:05 AM

That should say No HEAT or too much heat. While driving my sons new '86 126 home from its purchase I noticed that I either have lots of heat or no heat. A very slight movement of the dial goes from cold to blistering. I've read the monovalve can fail and result in no heat but this will supply heat. I'm suspecting the dial on the CCU. Any suggestions?

TX76513 · #2 11-14-2012, 08:35 AM

Just as a cost prespective and ease of DIY. Check out the monovalve, it will only take you 15 min and will either determine or rule it out. As a general rule when the seasons change my 126 needs a mono valve adjustment with a rubber hammer.

Silber Adler · #3 11-14-2012, 09:02 AM

My car had that condition too and the pipe between the dash intake and the heater was cracked. I replaced it with 1/2" pex. Perhaps you have checked that.

muleears · #4 11-14-2012, 10:28 AM

Quote:

Originally Posted by Silber Adler

My car had that condition too and the pipe between the dash intake and the heater was cracked. I replaced it with 1/2" pex. Perhaps you have checked that.

Nope, hadn't checked anything but here. I had done the duovalve on my 210 and suspected the mono on this one. But the slightest change in the dial changes from nothing to hot.

muleears · #5 11-14-2012, 10:29 AM

Quote:

Originally Posted by TX76513

Just as a cost prespective and ease of DIY. Check out the monovalve, it will only take you 15 min and will either determine or rule it out. As a general rule when the seasons change my 126 needs a mono valve adjustment with a rubber hammer.

I have a rubber hammer.... Just a few love taps to free it up?

TX76513 · #6 11-14-2012, 10:48 AM

That's my remedy. Just seems to stick between season change. It's not hard to take apart and clean. Very short tolerance on the cylinder, doesn't take much to hang it up. There is also the chance the diaphram has cracked a close examination will reveal. You can just get the kit to rebuild too.

While there may be another problem as indicated above - I prefer to check most common and easiest problems first.

rscurtis · #7 11-14-2012, 10:49 AM

I'm with Silber Adler. If the monovalve was the problem, it wouldn't respond to the temperature control. Check for air flow through the temp. sensor.

Walkenvol · #8 11-14-2012, 10:54 AM

I wish you would hurry up and figure it out as I've got the same condition on an '85 W201. Figured it was the dial / CCU and picked one up off a partster but not installed yet.

Jeremy5848 · #9 11-14-2012, 11:06 AM

I had a similar problem with my '85 300D (W123). Turned out it was a broken wire to the in-cabin temperature sensor, in that car located in the middle of the dash. Don't kmow where it is in a W126. I got full heat unless the temperature dial was all the way to the click-stop "COLD."

Jeremy

muleears · #10 11-14-2012, 11:26 AM

I *think* the temp sensor on this car is to the right of the glove box. I seem to hear the sampling fan noise from over there. I get home late this evening but I will try to poke the monovalve with my hammer and see what happens.

Silber Adler · #11 11-14-2012, 11:35 AM

The tube that connects the intake to the device is made from soft foam on my w123. It was sticky and disintegrating, It plugs into rubber tubes which were ok shape.

Once you pop the plastic rivets out and pull the glovebox you will see.

sleepstar · #12 11-14-2012, 01:20 PM

i had this exact problem. i had a bad temperature control unit. it's the silver box that is located behind the glove box. part # 0008221003. a little bit larger than a pack of cigarettes.

muleears · #13 11-15-2012, 04:29 AM

Thanks for all the suggestions. I didn't get home early enough to try any of them, I'll try to do so today. At least the hammer, I like that one!

vstech · #14 11-15-2012, 05:32 AM

Quote:

Originally Posted by muleears

I *think* the temp sensor on this car is to the right of the glove box. I seem to hear the sampling fan noise from over there. I get home late this evening but I will try to poke the monovalve with my hammer and see what happens.

the late 126 has the sensor near the sunroof controls. pull the light down and verify it's wiring is not damaged. the pump motor you hear in the glove box draws air across this via a rubber hose.

muleears · #15 11-15-2012, 08:53 AM

Quote:

Originally Posted by vstech

the late 126 has the sensor near the sunroof controls. pull the light down and verify it's wiring is not damaged. the pump motor you hear in the glove box draws air across this via a rubber hose.

Is that the rubber hose that is known to deteriorate or is it a different one?