I just changed our heater fan and i get air but no heat just air
need heat on 1990 GMC Rally Wagon 2500
is the motor running cold?check the fluid level in the radiator.
first you need to see if your coolant is getting at least a180 degrees. If you have a temp gauge it should be easy to check. If the coolant is getting hot enough the next thing is to see if the heater hoses are getting hot. Put your hand around one of the heater hoses while the motor is running and is warmed up. Then compare it to the other heater hose and see if it is about the same temp you shouldnt be able to hold your hand on either one for over a minute without it being to hot to hold. If one is r cooler than the other your heater core is stopped up. If they both fill equally the same and hot then you need to chech you