1990 Chevrolet Lumina

Heater problem
1990 Chevy Lumina V6 Front Wheel Drive Automatic 190000 miles

I have a 1990 Chevy Lumina 3.1 I have no heat the blower blows but does not blow hot air my coolant is fine and the engine temp is at normal operating temp. Is it the heater control valve and where is it?
Not sure if it is related but the day it started blowing cold I parked on a slope meaning the passenger side of the car was higher than the left when I ran into the store and came back out it was blowing warm and was fine the rest of the day the next morning it went back to blowing cold.
December 1, 2007.

This one sounds like an air bound system. Try removing the radiator cap and squeezing the upper radiator hose while it warms up, once you see the antifrwwze circulating in the recovery tank, make sure it's full then cap it. Here are the TS charts from chevy, this could also be a clogged core!

Dec 2, 2007.