If my car has been sitting for a bit, say 15-20 minutes, I start the car and I'll get some heat out of the vents for a bit till the outside temperature is able to overcome the leftover heat (sorry for the run-on sentance). Not a ton of heat, but just enough for me to wonder whether the valve leaks after shutoff.

This still happens if the car is sitting out in the sun for hours, the vent heat still needs to be purged while driving.

Is this normal mono valve behavior?

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)