Front aircond. blows warm. Rear air is cold

needs more freon

see if theres power to the rear blower motor go under the rear and see if the one pipe is cold and the other is hot or at least warm if there the same then the rear system is plugged

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 ?

Could be a blockage in the lines to the rear unit.
Might be low on freon too. Or a blend door problem.
Can you check under the floor and see if one of the lines is cold ?

Just a little low on freon can make it get too cold and it freezs if you in position to check the freon level you'll find with the system on high and the engine reved up the low pressure is below 25PSI. fill it to reved up is above 25 and your problem will go away. Low on freon will make it cold enough to frezze up and then warm up as the air does'nt go though the ice. it'll work good as you start up till it frezzes and after it's stopped up with ice it blows warm (it's really too cold). the more freon in the system the warmer it'll all blow because all the pressures are higher and it's the difference in pressures that make it cold.

With your front heat working the most likely cause for the rear heat not to work is that there is an obstruction in the line that is preventing the warm coolant to get to the rear heater core or the rear heater core itself is plugged and not circulating. Another possible cause could be low coolant level where the system has enough coolant to provide the front system with enought warm coolant but not the rear system. Hope this helps

a plugged orifice will prevent the front from becoming cold

The car uses the same freon in the front as it does in the rear. If the rear a/c is working, you either have a plugged evaporator in the front unit, or perhaps a bad heater switch. Try switching the heater to hot and see if it blows even warmer air from the front vents. If so, the heater switch is working and then it sounds like a plugged evaporator or maybe a plugged orifice tube. That is a good place to start looking. Hope this helps.

I recenly had the same problem on my 1999 suburban, even after I replaced the whole ac system.
The heater valve, which is under the air filter area was not closing, causing heat to be blowing over the evaporator core. I used a zip tie to keep it in the closed position, and ac went from 70 degrees to 40. I think the vacuum switch is bad, 40 dollars (dealer part). You can also pull the vacuum hose off the switch, which is on the firewall and connect it dirctly to valve and it closes the valve, but fits loosley. Use silicone around vac hose if you go this route.

you may not have enough refrigerant. a low charge can cause the rear in this dual system to not work for beans. charge with a can of uv and find the leak. fix the leak. evac the system and recharge. i think you take 4 lbs, but check the accumulator sticker. you may want to just change the accum at the same time.