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AC/heat Issues-HELP!

963 views 4 replies 3 participants last post by  MichaelAW 
#1 ·
1) Temp Dial set on min (cold), blower button on high: getting 11.5V at mono valve, hot air blowing.
2) Temp Dial set on max (heat), blower button on high: getting 11.5V to mono valve, hot air blowing.

AC recently charged, receiver/dryer replaced, system vacuumed, blower motor replaced, mono valve pulled out (examined) and replaced. Got cold AC for a little while yesterday, then hot air.

3) When blower motor was replaced I also flowed/re-soldered some contacts in the push button unit and got the blower working.

4) Pulled push button unit back out and noticed the temp dial circuit board circuits look "wrinkled". Continuity still OK but I'm not sure it works properly under load.

Posted elsewhere (other thread) yesterday that mono valve was getting first 10.5V, later 5.6V - however, now believe I didn't have a good ground on the meter.

First, will someone please let me know if the following makes sense:
a) Item 1 above indicates mono valve is faulty
b) Item 2 & 4 above indicate push button control unit is faulty

Second, suggestions as to the best place (price/quality) to purchase these units.
 
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#2 · (Edited)
Most likely your monovalve is bad and it stays "open" which alows the hot water to run into the heating coil. The AC could be working, but thats a different set of coils.
When the AC is on, check to see if the AC line that is along the driver side in the engine compartment is cold. If so, your air is working.
The bad monovalve is a very common issue. The internal seals commonly go bad. If you have hot water going out to the upper rubber hose that goes into the firewall you can try pinching it closed with a visegrip. and see if the air blows cold. I believe that the lower hose comes from the engine through a circulating pump.

There is a rebuild kit for the monovalve. It's a straight forward job. Pay attention to how the internal parts go when you remove the cover. Do a search on this forum and on MBShop forum. I think you will find lots of info. Hopefully the monovalve will be the issue. Good luck.
 
#5 ·
Mono Valve & Outside Temp Sensor

Mono Valve: took it back apart and examined. Assy looks line mono valve, small washer, spring washer, large washer. Then cylindrical ring with small notch at top aligned with tab in coil. Still doesn't shut off flow even though 11.5V is present no matter settings on push button unit.

Will replace unless get advice otherwise...

Outside Temp Sensor: When replacing receiver/evaporator I noticed the ceramic on the adjacent temp sensor was crumbling.

Could/does this affect the climate control system?
 
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