1993 gmc 1993 GMC Sierra k1500 5.7 Liter

[Daniel Hanson]

I am at a loss with this truck I have changed the heater core, Water pump, and thermostat last year, flushed the system and purged the air out of the cooling system and still only luke warm air coming out of Defroster and floor heat, A/C is not working it is unhooked and has no electrical going to it. Fresh antifreeze was also put in. Does anyone have any ideas. 

This is the heating and cooling system that pushes antifreeze to heater core from the top of the intake and then out of the heater core to the radiator (Not to the water pump). Water pump has a capped off inlet that I could run the hose from heater core to the water pump would that make any difference?  Also brand new radiator last year.

[Jsdirt]

Could have a blend door issue - probably stuck between full cold and full hot, or the door is leaking outside (cold) air severely.

 

If the heater hoses feel hot - if you cannot hold your fingers on them when the truck is at operating temperature, then it's more than likely a blend door issue.