GMC 208 sierra truck the engine hot sensor is on and the air conditioner won't come on

are you, in fact..overheating?...there are quite a few factors determining whether or not the A/C will come on.....running HOT isn't one of them...as you know the A/C has it's own "condenser" unit behind or in front of the radiator...probably an electric fan that comes on when the A/C is engaged and when par-boil temps are reached~.....check the charge of the A/C view the sightglass to see if it's contaminated with filter/dryer~ perhaps charge is low or terrible charge that leaked ambient air into that creating a mess for your filter/dryer~ would like it if you could present a cause and effect here, cause am not aware of any specific device that may be the cause of your frustration~

had same problem with my 2009 sierra.it sounds ridiculous,but i changed my thermostat and that fixed the problem.after replacing it i let it run about 5 min.and everything reset itself and works fine.$6 part

That's a main reasoning in my POV of most overheating issues however if changing out your Thermostat doesn't help it could be clogged lines or even a bad water pump and worst case scenario could be a bad brain box or electrical conduit / wire,of which would indicate a wiring check,many times a loose,frayed or missing wire can wreak havoc in a myriad of ways.