Front AC is blowing warm air

My front A/C is blowing warm all of a sudden but the mid and rear is blowing cold still. What could be causing this?

I do not have gauges but my whole system started blowing warm so I added more Freon and it started blowing cold again in the mid and rear. I checked the mode door underneath the left of the glove compartment that switches it from hot to cold and it was working. Then I checked the one under the right of the steering wheel that switches it from upper lower and defrost and it worked. There is one more that requires me to pull the dash but I am not sure what it controls. The clutch was engaged and running the whole time I had it blowing on high and it stayed cold in the mid and back the whole time it was blowing a little cooler in the front but nothing to be excited about.