Re: 01 jeep grand cherokee laredo heater issue
Since the problem could still be an air pocket in the heater core, i would start with this: put the jeep on a slope nose up and with the engine cold and radiator cap removed. Now start the engine and let it warm up. During the warmup the coolant expands and can/will overflow from the radiator, but check if you see any bubbles coming out. Air wants to go to the highest point and maybe with the nose a bit up the air pocket can move away from where it was stuck. Be carefull NOT to remove the radiator cap with the engine hot, because the system will be under pressure, and hot liquid will come out and cause burns.
If that seems to be ok, you could have a look at the blend door actuator. It is hidden behind the glove box door. Remove the door and you will see the blend door actuator. While moving the temperature selector, watch if you can see the actuator moving. If that seems to be ok, remove the actuator and actuate the door by hand. You could also see then if hot air will come out of the vents.
Eventhough blend doors are VERY common on the automatic zone control system, on the manual system they are not. Maybe a bigger change that the actuator is the problem, but still strange that the system was working ok before the thermostat change.