I have a 2005 mercury montego. Why doesn't my heater blow hot?

This sounds more like the issue. A few months back I was hearing a clicking noise behind the glove box and thought it may have been some sort of vac leak to that door. If thats the case whats the fix for it?

replace mode door,but fords have an issue with there heater box doors breaking best have it ck'd by a mech to be sure

I checked the core with an air hose while I has it all apart, filled the coolant and bled the system. Still blowing cold