I have a problem that I can not get heat in my car? It is a 1989 chevy astro van?

Replacing the thermostat usually fixes the problem. They can get stuck open and not let the coolant get heated properly. You can also have a very low coolant level. It sounds strange, but I have seen a vehicle with a very low coolant level produce no heat in the car. These are the 2 simplest solutions and I am more leaning to the thermostat.