What would cause 1994 GMC Sierra 1500 PU to overheat, heater and defroster to not work?

SOURCE: 2005 GMC Sierra Overheating

If your sure there is no trapped air in system after refill and air bleed off, is fan clutch pulling good air thru radiator? Even if it is, the heater should have coolant as hot as what temp gage is showing! Try backwards flushing heater core (dex cool is notorious for plugging these up). There is a TSB for cracked cylinder heads from GM for unexplained coolant loss.Remove drivers side valve cover, and look at center three head bolts for coolant around them, if coolant has been getting in thru this suspect area, there will be a milky/pudding like goo under valve cover and on head. GM had a company called Castec cast these and the areas near the head bolts were found to be too porous (NO recall YET!) Ya, you guessed it, replace heads! Unfortunately, if its gotten hot to many times, it has probably hurt the heads/gaskets. Hope this helps. PS: The castec logo is under the rearmost pair of rocker arms,may have to remove them to see.

SOURCE: 2000 gmc sierra 1500 5.3 v8. a/c heater control problem

your heat/cool and vent selection options are controlled by engine vacuum through small clear tubes attached to the rear of your climate control interface. Other vehicles have small steel pull wires that operate the desired changes. You might try removing the trim and any fasteners affiliated with the interface/console. GENTLY pull outward and look to see if any of these tubes are pulled off or cut/damaged. Did anyone recently install a new stereo in the vehicle? If so, the vacuum tubing and or pull wires that change your outlets could have been damaged when the stereo unit was pushed into place. Hope this helps

Testimonial: "Very good information. THANKS!"

SOURCE: I replaced heater core in 1999 gmc sierra 1500 5.3

no,, the system works from a vacuum and has to be worked on in a service garage. sorry about the bad news...

SOURCE: 2002 dodge 1500 Changed radiator, thermostat, and hoses. No heat

Why was radiator replaced?Did it have heat before ? If it was plugged, the heater core may also be plugged. Try flushing it with a water hose in both directions. I dont know why the botton radiator hose would be cold, the radiator should be a uniform temp and the air coming through the radiator should be HOT, when the engine is at operating temp. What condition was the old coolant? if it was rusty, the water pump may have lower flow than normal.

SOURCE: oldsmobile is overheating in idle only

my termas gage go up and down