No Heat

[erich7667]

I have a 1995 GMC Yukon 350 4x4. I recently replaced mt heater core and replaced almost all of my A/C. A/C works great but I'm not getting any heat when I turn heater on. I can see that the thermostat works on the temp gauge. I'm puzzled.

 

[Ironhead]

I'm wondering two things: Are the two hoses going to the right connections at the firewall, or is it possible thay got reversed when you changed out the core? Second thing: is there an air lock in the cooling system. If the truck overheats after running for a while, it is a sign of an air lock, and that's also a usual cause of no heat.