93 ford ranger blowing cold air only on heater setting. where do I begin troubleshooting, also I read about the heater treater blend door. Is this a high probability as my problem?

1. Check coolant level to ensure full, and thus getting to heater core.
2. If that didnt work, With engine hot and running, and heat on in the truck, feel heater core inlet and outlet hoses at the engine compartment firewall to ensure both are hot an thus getting flow. If not the core is clogged or there is a faulty valve in the flow path.
3. If te hoses are hot there is flow thru the core and either your blend door is broken and shut or the blend door motor or circuitry is bad.
4. You tube Ford Ranger blend door for video on how to access behind the glove box. You can fairly easily remove the motor and undoing so check its operation and also the blend door operation.
Likely your motor has gone bad and can be replaced using a low profile socket wrench to remove the 3 Screws holding it in place. I bought a new motor for $40 at One o te auto parts chains locally.
Good luck!

http://www.f150online.com/forums/hvac/216009-blend-door-replacement-pictures.html

Go to this link. You may change your mind on doing this project.

If you are sure the engine is getting up to temperature then your problem will be a part called the electrically positioned blend door and or the little motor that moves the blend door. The blend door moves back and forth between the AC core and the heater core to provide a mix of hot and cold air or hot or just cold depending on what you set the air temperature control at, blue being cold and red being hotter. This is all to common a problem on Ford rangers and Explorers which share the same components of the heating and AC systems. When the door fails it is usually on the cold setting position. The kicker here is that you must remove the dash to replace the parts, the blend door and the blend door actuator motor should both be replaced at the same time, the common reason for the motor to fail is a sticking hard to move blend door due to warping of the plastic it is made from.

Cold air like, really cold or just cool. Sounds like your hot/cold blend door motor has perhaps failed with the blend door in the semi hot position. Blend door motor failure is very common on the Ford truck HVAC systems. Is is located behind the glovebox on top of the HVAC housing assembly.

Heater core could be blocked up, or the blend door is stuck on the cold side of the a/c evaporator or the blend door is stuck in the cold position.

You likely have the dreaded "Blend Door" problem. In short, a piece of plastic that the engineers used to move the blend doors up and down was not up to snuff. As a result, the turning mechanism breaks, the blend doors fall down, and all you get is cold air. There's two fixes: One, you get a replacement Blend Door system from Chrysler and pay a dealer around $1000 to install it. (You have to discharge the A/C and remove the entire dash!) Or you can fix it using the "Heater Treater" fix. It's around $100 and you go in through the glove box. Just google "Heater Treater" for more info.

Probably broken blend doors if everything else is working, but its just blowing cold air. Do a google search for "Jeep Blend Doors" or "Heater treater" for more info.

Sounds like a classic blend door problem. They will start to break and exceed the sensor's travel limit, and then the controller will stop trying to move the door. There is also a known problem when the recirc door breaks, but it is less common. For more info, google "Jeep Blend Doors". For a fix, google "Heater Treater".

either bad recirc doors or a possible bad heater core. Open the hood and when the car is warmed up to mid point on the temp gauge look on the passenger's side firewall under the hood. You will see 2 black rubber hoses running through the firewall. Feel each hose and if one of the 2 are cold then you have a bad heater core. Otherwise most likely the recirc door.

Not an expert by any means, but i know my ranger.. I had a small leak at the top of my radiator that still cooled the engine but didnt have enough pressure to get to the heater. The heater hoses travel up over the engine and just were not gettin anything to my heater core. That or make sure the heater control valve is operating.