Chrysler: 2002 Sebring Sedan - no heat at idle

I just bought a used 2002 Sebring sedan (LX - 6 Cyl 2.7 L). The car
has 38k on it, drives well and I have not noticed any cooland loss.
The problem is that at idle, when the car is stopped there is no heat
output, when I speed up to about 30-40, the heat comes back strong.
Slow down, the heat goes away in 30 seconds. The engine does not
overheat, the coolant temp stays between in the middle range all the
time. It does drop by about 1 divison at highway speeds. Any ideas ?

Igor Cherepinsky wrote: 

Do you mean that the air through the dash vents is cold, or that there is no
air through the dash vents?

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Rickety