I could use some advice about my a/c on my 99 Tahoe. The rear a/c vents are blowing super cold but the front vents are warm. I also noticed that when I was sitting at a traffic light the front started to cool a little. It was still warm but definitely cooler than while traveling at speed. I checked the low side pressure and it was at 45 lbs. I can not check high side because I just have a cheap guage/filler set. I did accidently touch the high side line from the compressor and nearly burned my hand. Any help would be greatly appreciated.

There are two evaporators in the system. One for the front and one for the rear. Each one has an orifice tube which acts as an expansion valve and filter. Sounds like the front orifice tube is blocked or you have some blockage in that line or evaporator.

If the lines going to the front evaporator are cold, then it could be an air flow problem so see if the lines are cold.

If the lines are warm, then the orifice tube may be blocked.

//2000CAYukon

Thanks for the info. I will check it out and post my results so that it might help someone down the road.

are you sure that you have rear heat? I believe it was an option. My 00'hoe does the same thing, but I think it's because the vehicle only has rear A/C, no rear heat.
The rear A/C is a completely different unit (ever notice that water dripping fromthe rear passenger side), seperate and apart from the front. So the rear a/c isnt blowing the cold air from the front, it makes it's own. Don't think there's a heater back there.

are you sure that you have rear heat? I believe it was an option. My 00'hoe does the same thing, but I think it's because the vehicle only has rear A/C, no rear heat.
The rear A/C is a completely different unit (ever notice that water dripping fromthe rear passenger side), seperate and apart from the front. So the rear a/c isnt blowing the cold air from the front, it makes it's own. Don't think there's a heater back there.

There is no rear heat. The trouble i am having is with my front a/c. The rear blows cold the front does not. Someone on another site said that my compressor might be bad. He said the rear system did not need nearly as much volume or pressure to cool than the front system does. I am going to check the orifice tube this weeken. I will post my results.

thanks,
booker5time

I had the same problem with my 99 Tahoe, brought it to the dealer and they replaced a loose fitting/connection at the evaporator. They recharged the lines and I again have cold a/c in front.