2001 ranger vent problems

Hello I am having some problems with my 2001 ranger. It has the 3.0 v6. I thought it might be a vacuum problem but now I'm not sure. When I turn the heat on as time goes by its like the vent selector door looses pressure and I can hear the heat blowing like it should behind the dash but barely any is coming out of the vents. I used to be able to turn it up on its highest setting and it might fix it but now that will not work. I had been told that it sounded like the vac ball under the hood so I unpluged it so I would ay least have defrost. That worked but after some time like before it seems to start loosing air flow like it did before. Is there anything else this could be or that I can check? Any advice would be greatly appreciated

If your vehicle has vent operated motors doors for the heater Unplug at the vacuum motor and use a vacuum gage at the hose location check for vacuum. Check for vacuum at the temperature selector in the dash. Broken vacuum tubes are common. Plugged vacuum ports on the motor are common. Start at the motor and check at the firewall also then dash.