Posessed heat in 95 Jeep Wrangler

This is very annoying but during the summer, with the heating fan off, vents closed, HOT air constantly comes out of the windshield defrost. It makes it extremely hot in the car. Now get this. It just hit like 9 degrees out or colder and now there's NO HEAT! Any ideas? If the coolant level were low wouldn't there be no heat prior to the freeze? If I remember it did this last winter also. Please help, it's my wifes car and lord only knows what's going on with it lol.

Thank you guys n gals so much.

sounds like you are pulling fresh air into your defroster vents, which whould explain the hot air in the summer and cold in the winter. You must have the fresh air vent stuck open which allows the air to find its way in.

Ahh, you are probably right. But what about the heat? There's absolutly NONE coming out. A stuck vent would prevent this? You suppose this is something as simple as taking off the dash and fixing a vane or lever or is it more difficult to fix than that? It's my wifes car and I never really did too much on it. Sad to say neither has she. She has a chiltons manual and I'll be looking it up to see if I can find anything. Thank you for your quick reply.

Ahh, you are probably right. But what about the heat? There's absolutly NONE coming out. A stuck vent would prevent this? You suppose this is something as simple as taking off the dash and fixing a vane or lever or is it more difficult to fix than that? It's my wifes car and I never really did too much on it. Sad to say neither has she. She has a chiltons manual and I'll be looking it up to see if I can find anything. Thank you for your quick reply.
My 88 Cherk is doing the exact same thing. Makes it a bit cold at -20 (wind chill). Mine has the hot air in it but when it mixes with so much cold it just seems cold. You could swithc to vent while stopped to see if the air is hot (at lesst warm) and this should let you know if you are getting hot air.