The front air blows cold but the back air is blowing hot

not enough info does the front blow cold and just the back blows hot if so there is a mixing valve to let hot water come to the back so in the cold weather you can stay warm if the valve is bad it will let hot water to the back if the front is also warm you probably need a recharge and maybe a leak in the sys.

There's a valve between the front and the back that is supposed to open automatically. I have the same problem on my 1994, but in reverse, I get AC in the front, but it just blows hot in the back. I was told that this valve might be stuck... but no one would tell me where it was or how to get to it and no mechanic wanted to fix it for me. Apparently, if you can find it, it's easy to get it unstuck. Good luck.

possible blower motor

Usually a sign of low coolant or a blockage in the circulation.

HEATER NOT BLOWING COLD,NO HOT AIR FROM HEATER,A/C BLOWS HOT AIR,A/C NOT BLOWING COLD, COLD AIR FROM HEATER,BLEND DOOR ACUTATOR CLOSED,HVAC UNIT NOT OPERATING,
http://alltypesofpartsreplacing.blogspot.com/2012/12/heater-not-blowing-coldno-hot-air-from.html

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 ?

is it just the hot air that wont blow, or is it both hot and cold?

If you can get cold air blowing out the front vents, the front heater door is not working properly. If you don't get air blowing out, check the front heater fan and its resistor block.

check the AC relay...not the fuse but the relay

Hello according the the manual, the back vent are to blew cold air only..the fronts vents are suppose to the entire car...