A/c front and rear blowing hot air. have had the whole systems replaced.

Sounds as if you have more than one problem. If the rear is blowing hot then the AC is not working. The front should also blow hot if the front fan motor is functioning.Youi need to have the system pressures tested for proper freon levels and have the front blower motor system tested if it is not working

Is your heater blower motor working on all speeds ? Are you get any air coming from the rear vents ?

Sounds like one of the blend doors under the dash is not moving.

could be blend doors in heating duct work.

Could be low on freon, a faulty expansion valve on the rear system, or other issues. Can you tell if the rear ac lines are hot and cold ?

I would at least check the system to see if it is low on freon.

you have a vacuum leak in the selector switch for front heat explorers had similar problems

Is the correct type of heater core that use for rear heater?Check fan fix its correct side,or wiring change or return water line is blocked.

More than likely, you have a blend door actuator problem. Locate the faulty actuator under the dash, usually on the firewall, and replace.

no but there is a expansion valve u will need to replace