Only getting heat no matter what the temp setting is

I'm having a problem with my truck only giving heat no matter what the temp setting is.

Even when I turn on the air conditioning it spits out heat.

I'm not very mechanically inclinded but would like to fix this myself if possible.

Pete

need more info on trk!!! look at valve inline with heater hoses from engine to firewall first. have someone move the hot/cold selector switch back and forth to see if valve is opening and closing. start there!!! there is also a common prob with the blend door behind glove compartment so do the same at that valve with the other heater control(diverter switch)