My heat in my 2001 expedition doesn't work good and in the summer the ac doesn't work good.what can i do to fix that?

If you are talking about the belt for the ac compressor, yes the heater should still work.
If the blower is not working, you will need to have the blower motor checked for voltage and ground.

SOUNDS LIKE THE AIR BALL IS NOT LETTING IT CHANGE TO DIFFERENT LOCATIONS. MAKE SURE YOU HAVE GOOD VACUME

Common Problem On Expeditions Is The Vent Selector Motor , Located In The Passenger Side Compartment, Down By Your Left Foot !

is your engine antifreeze at correct levels is thermostat opening and closeing at correct engine temp theres a little door up inside your air duck that switchs it self when you switch from ac to heat it may be stuck open

This sounds like a vacuum problem. Check your vacuum hoses and connections as they relate to the HVAC system. There is a good chance that you have a cracked, broken, or disconnected hose, or a hose that collapses.

Your blend door in the Venture is on the driver side of the van, under the dash just above your right knee at the side of your plenum. You will see a white arm that will move to adjust the blend door. The blend door actuator sits on top of the plenum held down with 3 screws. If you did not want to diagnose the problem you could just wire it in place for summer or winter. Personally I would try and diagnose the problem. Hope this helps.

Hi under the hood the hoses going into the fire wall from the engine on one of the hose you have a valve which is open and close by a solenoid when it's defective it stays open check and close the valve

I had the same problem. Found out the the temperature control knob was on wrong, had to rotate it and put it back on. now it works fine.

I had similar problem on my 2001 Insight. Had to replace some cooling system hoses eaten by rodents... Works like a champ again.

check the vaccum lines inside the engine compartment. sometimes these get old and brittle from the heat and break.