No heat 300SDL - intermittent

[bhatt]

Hello all,

About 2-3 weeks ago, my heater started working "intermittently". Here's the data:

-Heater control set to 22 degrees (about 72 deg F). Also tried it with temp wheel clicked into 'MAX' setting.
-Button for 'ECON' selected
-Fan blower on 'AUTO'
-Engine temps seem normal (same as what they have always been every winter).

I start the car, and the heater works for a period of time. Not sure, but it seems like 10-20 mins. Then it starts going intermittent. If I stop & restart the engine, I can get heat to come out again for a while.. something is "resetting" when I turn the key off.

When it goes nuts, here's what happens: blower remains normal (usually at full speed since it's on AUTO), cool air comes out of vents. It's not outside temperature air, but it's not lukewarm either. Feels like about 40-50 deg F if I were to take a wild guess.

Any ideas? I tried unplugging the monovalve and drove for 15 mins. Seemed to still do the same thing (it may be in my head, but it seemed to go into it's nutty COOL mode more than usual)

Ready to pull the monovalve insert out & have a look.. but could this be the climate control???

Any way to bypass this for the time being? I thought unplugging the monovalve would do it (shouldn't it go into full HEAT?) but it didn't....

Thanks!
Neal