My heater is not working why?

Heater problem
1998 GMC Jimmy 6 cyl Four Wheel Drive Automatic

I am having a problem with my heater which has an automatic temp control and it isn't really working. It either blows really hot air or none at all. The air conditioner doesn't work now, either. Chevy garage said it is the automatic temp control auctuator or something else. He wants over $1,000.00 to fix it. I can't afford that, so has anyone else had this same problem and know for sure what is wrong? One person said it is probably the blending door. If it is one of these, how do you know where they are and what do they look like? Please help! Thanks in advance, brasshorse

Blending door is behind glove box(small release top left, bend down spring loaded tab then lower glove box.) Door is on right. Plastic gear can sometimes break. Can epoxy or replace or could be vacuum line has leak. Check vacuum first by disconnecting line and turn your climate knob from cold to hot(or vise versa) if you feel vacuum on your thumb then probably your gear

Im only getting high heat out of car vents no matter what I select on climate control selector. A/C works but its just not blowing cold air into vehicle. On heat selection, I cannot control heat either. Could it be blend-door broken or stuck in heat mode, or the blend-door motor failed, or climate control selector failed?

My a/c was recharged and the system is working normal. My problem is I select max ac cold and it blows as is the heater is on. Also even if I select just vent ac turned to cold position is still should suck outside air and blow somewhat cold but still dont. It all blows hot air. So ac system is charged right and heater is working properly so why does it blow hot when I turn it to ac vent or max ac?

I have the same vehicle, and the same problem. I'm going to replace or fix the temperature selector switch, which controls the damper door. May have to replace the whole hvac control assembly and or the damper door. While there I replace the heater core, hopefully I won't have to go in to the dash, wish me luck!

Heater problem
1996 GMC Jimmy 6 cyl Four Wheel Drive Automatic

Temperature gauge only seems to go to 160 even after installing a new thermostat. Heat is only luke warm at best. Is there any other valve in the system that controls coolant to the heater core? Is the engine temp not high enough and what else can we look for besides the thermostat?
The engine was replaced this summer, and the heat worked great last winter.

I have changed the thermostat and it is still not operating at normal engine temp - it runs cool. I have no heat but the vents work fine at all levels. Any suggestions?

Hello everyone.I recently purchased a jimmy and I spoke to the previous owner and said there was nothing wrong with it except that it has no heater and I would have to replace the heater core and so I did.I got nothing.I did some research and found that the heater cores tubes are supposed to be connected to either the engine or the radiator in order for anti freeze to enter into the core to transfer heat.I realized that the guy just had one hose runnin from one of the core tubes(larger opening) directly into nothing, so its not plugged into anything and the other one doesnt even have a hose.I checked the control valve and everything looks under control. Im not sure if my heater blower is working like it is but I get a feeling that isnt my problem right now so im trying to focus on this situation of the dangling hose. If you can please tell me where that hose(connected to one of the core's tubes) goes. Is there supposed to be a hose connected to something from each of the core's tubes?