intermittent cold air

[seyinark]

Help please!
I have a 1981 mb 300D. My symptoms are lack of consistant hot air at heat. Here is what I have done:
1) replaced acc unit
2)replaced mono valve twice with different brands.

The heat seems to come on when started and then go off. When I stand and idle it (usually) comes back on. Voltage to the mono valve reads 0 volts even though no hot air coming out (heat being called for). This summer I replaced the water pump. I wonder if the water flow is high and forcing the valve closed. Any help would be appreciated.

[qwerty]

Originally Posted by seyinark

I wonder if the water flow is high and forcing the valve closed.

That gets my vote.

Did you replace the monovalve? Or just the insert?

[seyinark]

just the insert