When I set the temp to max cooling it will coolfor about 1hour than the cooling stops and starts to blow warm ail.Fan speed is set to high.

Have you checked your low pressure switch?

Or may be gapping issue at the clutch. Check gap at the shims.

You have cooling for an hour? Then refrigerant levels should be ok, and your compressor should be ok....

How long do you drive your vehicle if you have cooling for an hour?

If it stops cooling after and hour, shut the A/C unit off.......then turn it on again at max, 60F, do you have cooling again?

Also, when there is no cooling, is the compressor running? Did you feel the lines going into and out of the evap?

Sounds like a control head problem.....

I am wondering if the low-pressure switch is stuck on, and after an hour the evaporator is frozen up with ice accumulation. Still need answers to the above questions though.

What if the water that'* supposed to be draining out, isn't draining out and is freezing up the evaporator?

When I turn the AC off after it stops cooling and tun it back on it still blows warm air. It is not heated air it is just warm air as if I just had the vents on. The truck has been parked for about 2 hours and if it still blows warm air I am going to stop at my mechanic and see if he can give some more answers to your questions. The Gm dealer wants me to try and pin point the problem,

thanks for your help

Good plan. A mechanic should be able to go through the questions we asked in about five minutes.

The dealer should be able to tell what the complaint of "AC on and not-cold air comes out". Pinpointing the broken part should be their job unless you asked "how much to replace the broken part without diagnosing anything". If they want you to diagnose for them then there'* something weird going on.

One more question, is this dual Auto Temp? If it is, is the complaint one side is much more cooler than the other?

OK, one more question, when it doesn't cool, is the A/C button lit?

I have had many arguments with customers, with the operation of the system.....and part of it is GM'* fault.....

Because GM makes customer'* think their control is a thermostat....and it isn't....it is just a setting...

I have been told by customers that they set their thermostat at 75, and they are comfortable at home.....

A car is not your home......

At home you set your thermostat, the fan comes on, the coolness is reached, it shuts off....

You auto temp is different, it has sun/load sensors, a variable fan, in vehicle temp sensors, and a control head that will adjust air speed and temp according to inputs....and that is what confuses customers.....

For example, the range on these units is usually 60(full cold) to 90(full hot).....if you had the old manual system, there was a temp lever.....all the way left was equal to 60...all the way right, was equal to 90......so where would a 75 setting be? Halfway, or in the middle with that lever.....how many times have you driven your car, in the summer with that lever in the middle for a/c? Never, you always had it all the way left or close to it, so the the 75 setting on auto temp is misleading.....

Another thing some do not understand, is if I command a/c on, how in the world can I have heat? It can happen under certain circumstances...let'* say you have your "setting" at 68, on a cool/moderate day...it'* possible for the system to override the the setting, if the inside temp sensor senses you have reached your temp(or if you have a bad sensor), and may actually be too cold, it will send heat/less cooling out of the registers.... another thing that may happen is, air flow may drop dramatically if the setting is reached...

If this happens, and customer don't like it, just go to manual mode.....

As far as your problem goes, when there is no cooling, is the A/C button lit, the compressor running, and do you feel cooling in the lines? If yes to all, then it'* a temp actuator(*) or control head problem...a "B" code may be set....

my mechanic bypassed the the low preasure switch and I had cooling for 3 days. I stoped shut off the ignition and started it up in about 5 minutes. all I got was warm ail no cooling.
What would be the next test so I can rule out the control head.
Thank You
Dave