For the morning I tried to turn my heat on to defrost my windshield but got nothing but cool air, move HVAV to heat position and still cool air any idea what the issue could be??? was fun driving to work with a foggy windshield.

 

Could be that the water control valve on the manifold quit working, or cracked vacuum hose on that valve.

 

Disasemble the termostat/water controll valve and try to boil it in the kitchen and see if its open, Well another thing you can do first is to check if the water hose is getting warm out from waterpump and the hose out from radiator. And the hose that goes in to the radiotor for the fan in to car.

 

If the thermostat turns out to be ok then the heater itself might have an issue.

 

Guys, the heater valve on these cars is normally open. They have been that way since 1971 on the full size cars. That is almost NEVER the problem with lack of heat. Much more likely on the 1977-1990 full size cars is a broken heater blend door bellcrank lever, found behind the glove box. Remove the glove box insert an look at the cable end when you move the temp lever from hot to cold.

 

I actually did have a thermostat go bad last winter and had the same problem as the OP. Eventually I could get warm air to come out of it, but it took like half an hour on the freeway for that to happen. On a cold start the thermostat is supposed to be closed, but if it's stuck open then the engine takes far longer than it should to warm up.

 

A stuck open or missing t-stat can certainly be a cause, but that's not the heater valve on the back of the intake that others were suggesting. Again, based on probability, on the 1977-1990 cars check the blend door bellcrank first. That is the most common cause of no heat on these cars and was so common that the aftermarket sold this part as a replacement (unfortunately, these cars are old enough now that the part is no longer available new). If that is good, then start looking at other potential causes.

 

Right, my bad. I misread your post.

 

Replaced the heater valve on the top of the engine last year. It was definitely stuck closed. My 75 88 heats fine now. Even with an open thermostat you should get some heat. With a bad heater valve you will get none. On the 75 the valve is closed unless one wants heat then the valve is opened.
Good luck...