OK So I changed the blower motor,checked fuses, in my 94 f-150,But I am curious if anyone knows why my ac/heater only works when I am moving when i sit still it stops it is really strange and just started happening, anyone know why? Thank you

 

Trying to understand the problem here in hopes of giving a better answer - is it that the warm/cold air doesn't come out the appropriate outlets, or that the airflow stops completely, or other?

Airflow coming out the wrong outlets - for example, coming out the defrost when it should be coming out the vent - is a sign that the HVAC system has a vacuum leak somewhere, made visible during changes in engine vacuum such as acceleration or idle. Typical cause is failure of one of the HVAC vacuum lines, most likely the one going to the recirc motor on the engine side of the passenger-side firewall.

Not sure about your model year, but if it has a vacuum operated temperature damper - the same incorrect changes could be seen. My vintage has a regular cable for the temperature.

If the airflow stops completely - hmmm, have to think on this a bit more.

 

no everything comes out where they are supposed to, it just stops completely when im at a light or not moving, but when i am moving it works fine

 

I am having the same problem in my 93 ranger about a month after changing the heater core

 

I figured it out on my ranger it was the fuse the fuse looked good but after changing it it works like it should. It might be worth a try!

 

i found that one of the wires came unplugged from behind the switch

 

If the loose wire did not fix it check the resistor by the fan motor, the only time the resistor is out of play is when you are on max ac with the fan on high.