F150 heater problems

my f150 heater won't heat up very good. takes 10 mins just to get luke warm. everything works as far as blower and fan. try to change theromsat and that didn't do it. does anyone know what it could be?

Feel the heater hoses and see if hot water is circulating thru the heater core. If not, you may need to flush the system. You didnt mention the year, some older vehicles had a heater control valve to control the water to the heater core. Later models do not, the water circulates all the time, and the heat is controlled by an air door, which is controlled by cable and the knob on the control panel. Make sure it is operating properly. The vent control, is operated by a vacumn motor under the hood. Its on top of the blower housing to the left, in the corner, next to the firewall. Make sure the vacumn line is ok, and it is operating properly. Also, when you changed the thermostat, did you make sure all the air was bled out of the block, and the system is full? If its low on coolant, the heater wont work properly.

It's a '97. I checked the hoses they were hot. thermostat is new. I have hot air on the floor but not on defrost. Could that be a vaccume leak?

Yes , it could be. Check the vacumn line going to the vacumn motor described above. It will be one small vinyl line, and the heat makes them brittle and bad about cracking. For some reason, rats, mice, and squirrels like to chew on em too. lol If thats ok, check the vacumn going in to the control panel. The actual switch on the control panel , gives very little trouble, its usually vacumn.