If the pressure goes UP on the low side with the compressor running I would start looking at your H-valve.

 

Sorry to job in like this,

However I just had an AC issue today as well. It's been blowing very cold forever now, then today it's just blowing warm air and no condensation dripping down. A couple of days ago the truck started to over heat while setting at Wendy's (maybe 15min) and again while waiting for the kids to get out of school(again 15 to 20 min). I was wondering if the thremostat could cause an AC issue? or low coolant ( the overfill bottle is empty)

Thanks, sorry to intrude.

 

Sounds like you may have a cooling system problem,possibly a thermostat. The a/c may just be a secondary issue because if the temperature goes up in the radiator, the condensor will not operate properly causing the pressure in the system to rise thus causing the high pressure switch to shut off the air. So check the cooling system and all is well then start looking at the a/c. Good Luck.