No heat

I have a '89 Corsica and there is no heat coming from vents just cold air. What is the cause and how do I fix it.

Thank you

How long have you had the car? Its possible that a previous owner had a leak in the heater core and just bypassed it.
Another thing to check would be the vaccum lines that operate the gate that directs the air over the core.
There is one vaccum line under the hood that wil screw all kinds of things up if it gets broken or disconnected. Next to the cruise control diaphragm you will find a vacuum T fitting. Make sure none of the lines connected to that are broken.
Since your gonna be digging around under the hood, its probably a good idea to check all of the vaccum lines, and make sure none of them are cracked broken or dryrotted.

I've had the car for about 4 years. Thanks you for the advice and I will check all the vaccum lines.

I had the same problem you are having. After about 3 days of trying to figure this out and tearing my whole heating assembly I found that there was blockage due to my AC. I had to take out my heater core and in front of that was the AC core ( I guess you can call it ) it was plugged up solid with dirt and stuff, I took removed it altogether where my AC was not working anyway and I started getting heat right after that. Only difference with mine was that no matter what speed my fan was on I was hardly getting any air/heat blowing from any of my vents at all.

Sorry but meant to mention this in last reply, usually the biggest cause for no heat only cold air is low coolant/water in the Rad or a stuck/sticking thermostat. Also make sure your RAd isn't air locked, this can happen if you have changed the water/coolant lately and put the cap back on before giving the car time to run and bleed out the air in the rad. A plugged up or blocked heater core may cause this to. Hope this helps.