A/C blows hot and cold

[corysam]

truckers,

i have a 1991 Chevy 1500 SWB. When i leave the house in the morning, the A/C works fine. It continues to work until the 1st time i kill the truck. when i retsart it, the A/C bows hot air. It usually stays that way until the next day but sometimes, it will start working again during the day. Also sometimes it will be blowing cold and then just start blowing hot air aga

in. When it starts to blow hot air, the compressor is still running. If i turn off the air, you can hear the compressor kick off and the idle change so the compressor seems to be working. I added freon about a month ago but it didnt seem to be low then. Is this a switch or something? any ideas?

thanks