My A/C compressor shuts off after an hour (sometimes longer) of driving on a hot day.

You could possibly have a blocked orifice tube or a low-pressure situation within the system. Sadly though, a high-pressure situation could cause the problems you're having as well.
Over-charging a system with freon can make the sensors and compressor freak out, thus, causing blowing cold one minute, then giving up the ghost the next when the compressor tries to cycle again. Most systems these days sense the high pressure and shut the compressor down to keep it from over-powering itself, and the lines.
Take it to a competent shop and have it tested or stop by a local parts store and purchase a pressure gauge for your A/C.

A few things could be wrong here. 1. if your running low on anti-freeze and your engine is getting hot, the thermal switch on the AC compressor will shut it off until it cools down. 2. You could be low on freon. 3. Your compressor may be bad with leaks.

What do you mean when you say it wont shut off? is it blowing hot air or do you just feel a lite flow of hot air even if you have the settings to cold?

If this is the problem that you always feel hot air at low flow and the ac goes to hot air then i would say one of two things, first if you have the selector to cold and you feel hot air then there may be a problem with the blend door, this door move to allow hot or cold air, the door may be broken or just a bad motor that controls it. keep in mind if the ac system shuts down for any reason the air then will be warm, it will be about the same temp as outside and maybe a little hotter.

this problem almost sounds like the ac compressor shuts off and then you are getting the outside air which is hot, there are many reasons for the compressor to shut off, it could be the compressor clutch heating up and disengaging , this would be due to a bad compressor clutch.

another reason is the fans are not working, the best thing to do is when the system starts to blow warm check and see if the compressor is running, start engine and look at the front of compressor, with ac off the front of it will not move, and then with ac on the front will spin, check it out and let me know, if it blows warm air and ac is not working then it may be compressor problem but if you are getting warm air and the compressor is spinning then it may be a door problem.

This is hard to check with out testing the system, so i listed a few things to check and let me know the out come. also the ac blows cold for how long before it gets hot air blowing out of the vents, good day.

Look under the car when it stops and after the engine is turned off, do you see a lot of water dripping under the car on the passenger side? If so the AC evaporator core is freezing up and the pressure switch is defective. If scenario this is not the case then you may have either a sticking compressor magnetic clutch relay or the magnetic clutch closing coil is shorted when it is hot.

Check the blend door actuator to see if it's working

I would check the following possibilities:
1. Is compressor clutch working? - You need to do this when the ac is blowing hot air only - locate compressor drive pulley on engine - rubber belt wraps around it. Start engine and set to max ac. When the ac is blowing hot air, look at the center of the compressor drive pulley using a good flash light - watch it for a while, it should be spinning with the pulley - this means the compressor is engaged. If not, the compressor is not engaged. If your ac is blowing hot air, then the compressor should be engaged and running (trying to cool). If it is not engaged, then your compressor clutch is probably going out. Could be low voltage to clutch, but more likely the clutch is worn out and only working some of the time. Note: if working normally, the compressor clutch will engage and disengage in cycles- but the air should always be cold. If clutch is bad, compressor would need to be replaced (sold as one unit). This is tricky to diagnose and could take some time - you need to do it when ac is blowing hot air but set to max cooling.

2. Low on refrigerant or refrigerant has moisture in it? If your ac blows cold initially after being off for a while, then heats up, and continues to regularly cycle back and forth between hot and cool air, then the system may be low on refrigerant or the refrigerant may have moisture in it that is freezing and restricting refrigerant flow. An a/c shop can check refrigerant level and even replace refrigerant if moisture is suspected.

Could be other issues, but I would start with these.

Good luck

your ac compressor is freezing up try not putting it on cold all the way. put thermostat towards the red jus a lil but still on the cold side to see if that helps

Anything to do with A/C not working is either
Belt, a/c/clutch,broken feed wire or fuse OR your out of GAS its called R12 i think
Take to Aircon station and they can fill if need be in 1/2 hour.
Have a goodday

sounds like a vaccum diaphram may be leaking try listening for hissing noises under dash near the glove box,set blower to lowest setting\off if you can and still have a\c on.

Hmmm... its gotta be the compressor.