My 1997 ford f150 heater blows cold air in winter and hot air in

sounds like a faulty sensor

Blend door stuck.

Make sure the cooling system is not plugged up, poor coolant flow can make your engine run hot, and a plugged heater core will not allow heat in the cabin in the winter.

bad heater control switch or resistor.

It sounds like the system is fried. Based on the description, it is just pulling in the outside air and not doing anything to heat or cool the flow. Unfortunately, this is a job for your preferred mechanic.

hi Planeman.
Why is the heater in my car not working? Ken Mattson, owner of Len's Automotive in Bellevue, Wash., says a car heater can stop working for a number of reasons, including: A low antifreeze/water level in the radiator due to a leak in the cooling system. A bad thermostat that isn't allowing the engine to properly warm up.11 Dec 2013

Why Isn't My Car Heater Working? ' Angie's List

https://www.angieslist.com/articles/why-isnt-my-car-heater-working.htm Search for: Why is the heater in my car not working?
Why is my car heater not blowing hot air?Hot coolant from the engine passes through a heater core, which looks and functions a lot like a small radiator, and a blower motor forces air through it. ... It's also the reason that a plugged heater core, stuck thermostat, or air in the cooling system can all cause a car's heater to blow cold.9 Jul 2017When Your Car Heater Blows Cold Air - Lifewirehttps://www.lifewire.com/when-your-heater-blows-cold-air-534667
How do you fix the heat in your car?Begin with the vehicle on level ground, engine off (cold) in park with the emergency brake set.Heater Controls. Step 1 - A heater cannot operate unless the engine is full of coolant/antifreeze. ...Refilling Cooling System. ...Engine Thermostat. ...Blend Door Actuator. ...Broken Vacuum Line. ...Heater Control Valve. ...Vacuum Gauge. ...Heater Core.How to Fix a Car Heater in Under 30 Minutes - 2CarPros
What are the symptoms of a bad thermostat?A motor with a bad thermostat will run fine for the first few minutes, then overheatrapidly. Other symptoms include the engine and radiator making a rumbling, gurgling, boiling sound: like a steam pipe knock, if you've ever heard one of those. A thermostat sticking open can make your heater not work in the winter.Auto, Car, Truck THERMOSTAT Repair bad thermostat symptoms
or go to this link if you need more help.
2008 ford ranger has heater that won get hot Google Search

Could be a couple of things.

1. May need to replace your thermostat ($10 DIY)
or
2. Heater core may be bad

Make sure that the tubing around the accumulator is getting cold.
If not, the refrigerant may not be charged up.
Otherwise, the vacuum motor for selecting cold air may be not working correctly causing heated air from the heater core to be routed to the interior of the car.

Do you hear the vacuum motors working when adjusting the heat to cold selector? or changing the thermostat temperature if so equipped?

your problem is caused by the air temperature control blend door actuator motor being defective, the little motor moves the door that gives either hot air or cold air or a blend of the 2.

guys have you checked for a vaccum leak????? there is a little plastic ball with a vaccum line going to it that controls the outside air coming in. check for a leak in this line