1998 GMC Truck

Heater problem
1998 GMC Truck V8 Two Wheel Drive Automatic 170000 miles

need the location of the heater controll valve in my truck. Heater will not get hot, ever! I can feel one of the heater hoses and it's hot, but the other one is cold. What seems to be my problem?
December 4, 2009.

There should be a water control valve in one of the heater hose lines with either a cable to it, or a vacuum line. See if you can move the valve by hand. If it moves freely, either your cable is bad, or you have no vac, or vac at the wrong time. If you have a vac line, pull it off and see if the valve moves, also see if you have vac. Move the temp control lever and see if you get vac in either hot or cold position. Hope I helped you out. Mickey-d

Dec 31, 2009.
Flushed the heater core and that was it. Flushed it backwards. Before there was no, I mean NO flow comming out with a H2O hose from house hooked up to outlet, and inlet opened to the air. Just used water! WOW what came out was black and dirty! Thanks. Pat

Jul 7, 2010.