Good Afternoon, I have done a bunch of reading and testing, but haven’t found a solution to my no heat problem.

A little background first. I have owned the car for a couple of years. Has always had a no or sometimes low heat issue. The car spent 95% of its life in Florida.

As part of some ongoing maintenance and in trying to resolve the no heat issue I have done the following. I replaced the thermostat and the car consistently runs right around 85 degrees. Replaced the coolant with the proper Zerex formula after the thermostat replacement. Replaced the duo valve with a brand new Mercedes part. For a little while the heat worked after the car was up to temp, but only if the fan was on the lowest setting. Anything higher and the temp would get cold. For the last few weeks I have had no heat at all.

I have also unplugged the electrical connection to the duo valve as I read that should result in heat all of the time. Still no heat.

What should I look at next? Driving me crazy as this is my snow car with heated seats and snow tires. It’s in the 20’s today and snowing in the mountains of WV.

Thanks in advance.

__________________
Greg

Current
2005 E320 CDI (50k) W211 with OM648
1999 E300D Turbo (133k) W210 with OM606.962
1997 E300D NA (170k) W210 with OM606.912
1991 300D 2.5 Turbo (199k) W124 with OM602
1990 300D 2.5 Turbo (170k) W124 with OM602