I could use any advice anyone can give on my heater. The heater will work one day in the winter, and then not work at all the next. It only does this in the morning the first time the truck is started that day. Later in the day after work it will work fine no matter what it did that morning. When it does not work in the morning it will just blow cold air the whole way to work, which is a 20 minute drive. On days when it works it kicks in like a champ as soon as the engine warms up. I tried replacing the thermostat and it did not help. The a/c never has been any problem though.

There shoud be some sort of mixer valve or door arrangement to mix hot air coming through the heater core with outside air to control the temp. Check the plenum and door under the dash.

Once, I had an occation to drive back up North in October. The heater door on my Mustang was stuck shut. The gasket had melted onto the plenum. It had been three years since I had used the heater.

Jack

The rotary control for selecting where the air comes out directs vacuum to a couple small vacuum motors that move the dampers or doors that jtbirdsc is talking about. If you pull the bezel off and check that valve, you may find it's sticking and not selecting the outlet correctly. Or it could be that the line that feeds vacuum to the control is drawing closed and not allowing vacuum to the control. We have a 95 Grand Am for a 3rd car that has the same problem, sometimes it works, sometimes it doesn't. While you're in there, check the cables for you heat selector and see if it is working. It might have broken on the end and is just catching once in a while.


Welcome to the board too! :)

Thanks for the direction I will most definately check that out.