The air just blows cool air in the front when I put the temp. up, but I can get hot air in the rear. Why?

I would check the blend door actuator. If the door is open all the way, one direction, the air blows over the heater core. All the way in the other direction, the air blows over the evaporator. Anywhere in between, a blend of hot and cold for temp control. That explanation is a little simplistic. the info is for ford windstar.

This model has a rear heat/cold blend door actuator. Its an electric motor that moves the duct door from hot to cold. When they wear out, they're usually stuck on the last setting

your auxillary fan is not working. this fan is responsible for cooling the freon that is being circulated in your cooling system... check if there are any loose wires in front of the engine bay.

the auxillary fan is located right beside your radiator fan.

Hi John,
Your right with your diagnostics, you have a blend door problem. If your switching to cool air and it is still hot then you also have a heat exchange unit fault, this is the component that changes the water flow from hot to cool by shutting off. If it is not operating correctly this will give you constant hot air no matter where you temperature switch is positioned.
As for the warm air while the engine is cold, sounds like the blend door is still open to atmosphere tempreture and if it is hot outside will pull that hot air into the inside of the vehicle.
Have the heat exchange valve checked, and the only way the check blend door operation is to remove the wiring from the blend doors and have the circuit tested. If the circuit is ok then the blend doors will need to be replaced.
Hope this helps

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

If you still get cold air out of the rear vents but the front only blows hot air you may have a bad temp door actuator in the dash, it may be stuck on hot and not able to move to cold air. However if you are low on freon with a truck that has front and rear ac then there will be a temp diff between the two. If it is hot air out the front like the heat is on then you have that actuator problem but if it is cool air about the same as the outside air temp then you may be low on freon.

check the vacume / or the vacume regulator for the door exchange from hot to cold there might be a vacume problem.

this is caused by the main cabin temp blend door actuator motor, in order to replace it or even check it the dash must be pulled out.

Hi, my best advise is to have your air check for freon leaks ,low freon causes the compresor cluth to stop working ,this can cause the air to blow hot .......

There is only one A/C system split into 2 zones. Check the blend door actuator, it may have failed in one position or something may be jamming it. Also check the control panel in the dash, My 98 yukon did the same thing, no matter what temp you selected for the front it would blow at about 70 degrees. There is a circuit board in the control panel that gets corroded and one of the circuits controls blend door operations. Have a look.