2000 Ford Expedition Heater

When you turn the temp gauge on your console do you hear the door moving at all? If you have a a heater control valve then check to see if it is getting good vacuum. Check to make sure you are not low on coolant with an air bubble in the system. Do you get heat with the rpm's raised above 3000? If so then you have air in the system. Check all the heater hoses at the heater valve to see if all the lines going away from the valve are hot. If they are not with the heat on the I would suspect your heater valve is not opening. You can always just get a small piece of pipe and directly connect the inlet hose straight to your heater core supply to see if you then get heat. That would also tell you that your valve is not operating. If you have a hand held vacuum pump you can apply vacuum manually to the heater valve to check for its operation.

Ok, since you feel the air get stronger when switched to cold then that may be a sign that the blend door is working. Is the vacuum line going to the heater valve on securely? Have you tried raising your RPM to about 3500 for a few seconds with the heat on to be sure there is not air the system (also with the engine cool, remove the radiator cap to be sure there is a good coolant level. I would even leave it off while you do the RPM cycle to be sure to push all the air out it there is any). After those tests, If you still do not get heat then I would suspect your valve. The valve should be in the engine bay with a gray vacuum hose going to it I believe, and of course heater hoses attached to it. All you have to do to replace it is remove the hoses on the valve and the vacuum line, then just pop the new in. Of course you will need to top off your coolant and purge all the air out of the system.

Its ok, just make sure to update me on how you next test goes, so we can be sure we correct the issue.