W126 '83 380 SEL - No heat, dry mono valve. - PeachParts Mercedes-Benz Forum

bolomiester · #1 10-27-2007, 08:04 PM

I've been following threads in the archive regarding NO HEAT. I changed the thermostat (Berh + MB antifreeze + new hoses + new radiator), and installed a new mono valve kit but I still have no heat. Air conditioning has always been ice cold.

The weird thing is, when I changed the mono valve it was totally dry inside. So dry there was a small cob web in it.

Can anyone suggest the next place I should look? Plugged heater core? Plugged auxillary water pump. Something else stopping the coolant flow before it reaches the mono valve?

The good news is, the engine now reaches normal operating temp, runs stronger and shifts smoother, but it's gettin' cold out there!

Small Note: The car was very neglected before I bought it.

mercmad6.3 · #2 10-27-2007, 09:45 PM

Some one has blocked the two hoses at the rear of the heads.
Pull the one nearest the monovalve,jam a garden hose down it so it pushes water into the engine,with the radiator cap off. No flow means it has been blocked to fix a heater that wouldn't shut off.
Theres is also every chance that the spigots on the heads are corroded up.
it also sounds as though your compressor is not shutting off pointing to either one of the control solenoids hooked up incorrectly or the dial control needing a bit of attention.

bolomiester · #3 10-28-2007, 10:34 AM

Intentional blocking of the coolant to the heating system seems likely as prior to my ownership the car spent its entire life in Florida and had fallen on hard times in the last few years.

I'll dig into things today and see if I can find what's blocked up.

bolomiester · #4 10-28-2007, 05:39 PM

mercmad6.3
WOW, That was a rifle shot right to the bullseye! When I dug in I found that the hose to the auxillary water pump and the return from the heat exchanger, were connected to nothing. In their place a hose had been installed that connected the the two spigots on the heads together, thus leaving the heating system completely insolated.

My poor old, cold fingers couldn't be made to work in such a confinded space so I'm letting my local mechanic hook it it right tomorrow. Hopefully the second half of your prediction will be true also, and that it was done to correct a heater that wouldn't go off and not for a leaking heat exchanger. I'll post the results.
Thanks again,
Bob

bolomiester · #5 10-29-2007, 05:02 PM

The bypassed heater system turned out to be the only problem. Once the foreign hose that was connecting the two heads together was removed and the two hoses to/from the heating system were connected correctly, everything works great! No leaking heat exchanger.

Thanks again to mercmad6.3 for that brilliant deduction. I was ready to tear out the mono valve and aux. water pump. I would never have occurred to me to look for such a simple solution.