Question: We have a 1997 ford f150. My husband replaced the thermostat, but it still reads cold and doesn't put out any heat. Any suggestions? We are in Ohio, it's December, and it's freeeezzzing - need heat! Thanks for any help.

Answer: 
Make sure the cooling system hoses aren't kinked and are routed properly.

Make sure the coolant levels are good. If the coolant level isn't proper, there could be an air bubble in the heater core which would prevent/hinder the heat.

Is it not blowing? If so, check the fuses - specifically the engine compartment fuse box, slot 6 (3rd from the front, left column). That's a 40A fuse that is for the blower motor. If the fuse blown there is a good chance you have some electrical issues.
The first checks are to check that the cooling system is full of coolant. The next thing to do is scan the AirCon/heater assembly for correct working of the heater flaps. 

On You Tube you can find a three part video on just what it takes to repair the heater flaps on your system. The heater flaps break on a lot of occasions, and when broken will not allow air to pass through the heater radiator to be heated.

You Tube: "F150 Heater Core part 1". Also part 2 and part 3. Part 3 will show you the heater flaps and how they break.