I've had this for 4.5 years and put 30K on it: new diff, clutch and shocks replaced, regularly change oil and keep it well maintained. It has always run hot with the gauge at @ 1/2. First time using the heat in months the other day, and it's blowing cold air regardless of setting. Someone said it might be the thermostat but that doesn't make sense, because in my past experience with no heat the thermostat was stuck open and they usually ran cool too, but the gauge is still at the half-way point.
Also, looking up thermostats I see just the regular metal unit that I have always seen and one that's plastic and like a full housing where the thermostat.
Does anyone have an experience with an issue like this or know what the problem could be?
TIA for your help!

 

Clogged heater core?
There is a vacuum reservoir which actuates (closes) a blend door when "MAX AC" is selected. I suppose that's for windshield clearing.
The heat side of the air box is closed off. Perhaps that door is stuck?

 

Common "No Heat" in cab, or "No Cool air" in cab, in all 1995 and up Fords, is a failed Blend Door Actuator electric motor, as said common Ford issue, so Rangers are effected as well

Google: Ford Ranger Blend door actuator

Lots of videos to watch, and posts to read

With engine off and key on change the TEMP **** from cold to hot and back, you should hear the blend door moving
Blend door actuator is powered by fuse 27, 10amp, in cab fuse box, long shot but FREE to check that fuse

The Blend door directs the air flow from the blower/fan as it comes into the cab duct system
Temp **** on COLD directs ALL the air AROUND the heater core, by-passes it
Temp **** on HOT directs ALL the air thru the heater core
In between settings are the adjustable "air temp control", some air thru heater core

This is the only temp control on any vehicle, just FYI
AC is on or off, no temp adjustment, its just mixed with warmer heater core air if its too cold for you and you adjust it