my heater worked really well before i did my swap in my 90 hatch just did the swap on sat-sun and now that i have the new motor in the heat does not work at all it just blows cold air.

what could this be?

thermostat?

air in the coolant?

waterpump? im really thinking mine is still good because the car does not run hot at all stays at normal level.

timing belt is fairly new. im going to check the fuse for the controls as well as get a new thermostat today if i have time just wondered if it could be something else as well