Originally Posted by MADDOG
Agreed ^^^^ If it was working before, then the coolant issue and the heater core need to be looked at.
If the HVAC functions of defrost, vent, heat, floor, mix don't work, then it's the HVAC blend door, which is a common issue.
The thermal relay on the passenger's side floor board up under the glove box-towards the center is another thing worth checking in the hopes of not having to do the blend door which as MD said is a common cause.
I'd turn wrenches on the water pump to repair the obvious problem and see if a proper coolant level alleviates the problem...if not you've got a couple of good leads to follow.
By the way... The fan is threaded to the water pump. Pull one of the 13mm bolts on the pulley behind it and stick a screw-driver in the hole to keep it from spinning when you turn the large nut COUNTER-CLOCKWISE. (That was a preemptive post)