Air conditioner only works on high

Hello good day what's going on is your blend door is cracked , or the blend door actuator is is going bad (motor that moves blend door)

Usually there pretty cheap if you can find them more of a pain to get to dash or trim usually covers parts.

But it will be inside a plastic box and all it does is open and close more depending on how you adjust knobs in car generally in Center of car or a little toward passenger side

Ford Ranger uses the heater control valve when heater AC unit is turn to the max AC it applies vacuum to the heater control valve which shuts off the hot water to your hear Core when you turn it to regular AC position check the heater control valve make sure it's still getting vacuum if it's not getting vacuum it is your heater controler (control unit in the dash ) a easy way to check this is to apply vacuum to your heater control valve while in regular AC position if now you have air conditioning from Max AC and regular AC .