Heater blows cold air.

[jpopp1]

I have a 2001 Ford Explorer Sport Trac with a V6. The AC worked good all summer long but now that winter is here the heater just blows air. After about 15 minutes its finally warm in the truck. I checked the blend door actuator as best I could, it was making noise when rotating the knob from hot to cold and back. Removed the glove box to gain access.
I don't think it is the actuator but something to do with a vacuum line. The temp gauge stays in the normal range during operation, coolant level is good and one hose leading to the heater core is a little warmer then the other. I have replaced the broken vacuum lines under the hood in the engine compartment but might have missed one.
Could the problem still be a vacuum line, blend door or something to do with the thermostat? Been looking through all the forums but keep running in circles. Any advice?

 

[Markaprice73]

check the vacuum line that is connected to the heater control valve. HCV should be located on the heater hose just before going back to the water pump. When the max a/c is selected or control dial is in the OFF position this applies vacuum to the heater control valve to shut off coolant flow to the heater core allowing coldest a/c possible. Anyway, if the vacuum line is ok, then the heater control valve may be stuck closed or slightly closed not allowing full flow of hot coolant to heat you core faster. The reason I'm thinking this is you say "one hose leading to the heater core is a little WARMER than the other". I say"one hose should be a little HOTTER than the other". That's why I think flow may be restricted. OR your heater core itself/heater hoses may be clogged and needs to be back flushed. It is possible if you only used max a/c all summer coolant never flowed through the core and hoses causing a clog. Let me know what you find. I am no expert. But, I have been studying our ST's coolant system a lot lately as I am getting ready to do a full OCD flush,back flush,change hoses,rad cap,thermostat,gasket,core back flush,clamps,distilled water,etc...

 

[Markaprice73]

or could be time for a thermostat change ..couldn't hurt

 

[ncranchero]

Check the blend door