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  #1  
Old 09-25-2007, 02:52 PM
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no heat on a w123

83 w123 euro. after letting the motor run till operating temp i'm not getting any heat at all from the heater. motor is blowing fine. flushed the coolant the other day and still have a problem. what are the main things to check for?

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  #2  
Old 09-25-2007, 03:11 PM
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Check the monovalve.
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Old 09-25-2007, 05:02 PM
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Mono valve failure usually results in heat all the time, as the diaphram is torn letting hot water through regardless of dash settings, I think. Otherwise, heater core?
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Last edited by toomany MBZ; 09-25-2007 at 05:03 PM. Reason: more info
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Old 09-25-2007, 05:17 PM
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Quote:
Originally Posted by toomany MBZ View Post
Mono valve failure usually results in heat all the time, as the diaphram is torn letting hot water through regardless of dash settings, I think. Otherwise, heater core?
On my 85 300TD, I had no heat.

Rebuilt the monovalve (torn diaphragm), now I have eyeball melting heat on demand.
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Old 09-25-2007, 07:10 PM
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Check your aux water pump, its purpose in life is to push hot water into the cabin.
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Old 09-25-2007, 07:31 PM
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aux water pump is located where? and i assume the monovalve is on the firewall? i moved the two white levers on it and heard some gurgling (with the car off) so sounds like that monovalve isnt getting activated or is stuck closed.
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Old 09-25-2007, 07:33 PM
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read that the valve is normally open and closes with 12v is applied. any reason why this would have been stuck closed? the car did sit for a couple years.


*edit*
still no heat. how do you check the aux water pump?
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Last edited by mcguiver7; 09-25-2007 at 07:48 PM.
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Old 09-25-2007, 08:17 PM
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ok moving right along here. hose going to the monovalve is warm. two hoses coming out going into the firewall are not, and both were squishy. i pulled those hoses off and theyre bone dry. i started the car pulled the hoses from the monovalve going to the heater cores and operated the valves manually. no coolant came out so i assume the monovalve is clogged or aux water pump is bad.
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Old 09-25-2007, 09:51 PM
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It's a Euro. Do the manual heater controls on a Euro involve a monovalve? I suspect not, but I might be completely wrong.
The fact that the poster refers to manual controls on the monovalve indicates to me that there is a 'failure to communicate'.
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Old 09-25-2007, 10:23 PM
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Unknown on the euro mono valve thing, yes it is near firewall. Mine has a heater hose going into the bottom, one coming out toward the driver, and an electrical plug on top, I don't see any levers. Anyway, an easy inexpensive swap out, if necessary. Aux pump is in line on passenger side near expansion tank, can't miss it, if there.
D.S, good to hear you have more heat than you need. I have replaced the MV on principle, no other reason, wasn't even necessary.
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Old 09-26-2007, 12:25 AM
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sorry i did not know the correct term for it. i just refered to it as that because it was mentioned earlier. mine has the one hose going to it from the thermostat. and two hoses coming out of it. it is mounted on the firewall with no electrical connectors. two cables come out of the firewall and control the two valves. i guess that does mean it's mechanical. i'll pull the valve in the morning and check for obstructions.

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