How to find heating problem on 96 GMC Sierra 4.3L?

Make sure that those new actuators are working properly and the blend doors are moving. You didn't mention the Mode Door, and that's the first place I'd look, it controls hot/cold- ambient temperatures. If it's not moving off cold, you won't get heat in the cabin.

Make sure that those new actuators are working properly and the blend doors are moving. You didn't mention the Mode Door, and that's the first place I'd look, it controls hot-cold temperature switch. If it's not moving off cold, you won't get heat in the cabin.

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Temperature door under the dash is stuck, broken, or the actuator is not working. If it's vacuum operated, check your vacuum hose connections. If it's electrical, remove the actuator and move the selector from hot to cold on the dash. See if the actuator is working. If the actuator is mechanical, has a cable attached to it, make sure the cable is hooked up correctly and not binding. True story, when I was in high school a friend and I went to a concert. Coming home it was cold out and she said she wished the heater worked. I slid the temperature selector to hot and turned on the heater. It was nice and toasty! She asked what I did to fix the heater. I told her nothing. Then she looked at the control panel. "OH," she said "You put it on hot! Isn't it supposed to be on cold because it's cold outside?" I laughed and said "Um, no, it's supposed to be on hot right now because we want hot air to come out!" Hope that helps! Jim

I don't think its the mode actuator. I pulled it and tried to see if it would turn while it was out. It doesn't click or turn. I tried the new one and it doesn't turn either. Could it be the temp control module?