Front Air works great, Rear air only blows hot

Ok, here's what i have:
2001 Tahoe
85k miles
fully loaded (sunroof and all) ...only 2 wheel drive

so my front air conditioner is great! my rear air only blows out hot air. if i leave my front air on max for 15 mins while driving, the rear air will low slightly cooler air but it's still hot.

i've already added more freon (134a) and it just made the front colder, nothing for the rear.

any suggestions? i'm not exactly rich so the cheaper the better.

Automatic or manual and does it have sun roof?
Any ligts flashing or on?

First check for a proper r-134a charge.
Just adding a can is not the way to go about proper charging.
Was that a can of wall mart killer death kit stuff with the stop leak and any fit all oil stuff?

Give us you low and high side readings at Idle and at 2K with compresser running.
MY

How do I check the readings u are asking of? (I'm mechanically minded but I'm a girl)

The sunroof is operated my a button located in the upper console with 2 overhead lights and my rear air control.

No lights are unusual. Sunroof still works.

There are three knobs dealing with the rear air. The first is "off 1,2,3". The middle is the red/blue temp change. The third is the head-mix- and feet knob. All knobs work. Except the red blue temp one doesn't go to the extremes it should. The blue is hot and the red is hotter.

Oh! And the freon was from napa.

To check and recharge a ac you need a low and high side gauge kit.

http://www.ackits.com/merchant.mvc?Screen=CTGY&Store_Code=01&Category_Code=RefrigerantGaugeSets

http://www.ackits.com/merchant.mvc?Screen=CTGY&Store_Code=01&Category_Code=DIY

If it is auto matic ac controls a good body/HAVC capable scanner will check thing out and read any codes.

If you do not have the proper tools to do it it would be best to find a good repair shop and have them check it out.
Good Luck
MT