On my 2004 ford ranger my A/C blower just works on speeds 1 2 4

You have a bad blower motor resistor ! It's near the blower motor ! has four wire connector to it ! The orange an black wire at the blower motor comes from the resistor !

Blower Motor Resistor 1AHBR00036

Most likely cause is the blower motor resistor block. 1,2and 3 go through the resistor forth speed is is full blast therefore bypasses the resistor being the only speed setting that works when the resistor has failed

check your axles u joints are probley bad.

sounds like someone may have added a switch to bypass a bad dash switch ? Could be if this is new problem and you had this car awhile that the switch guts are broke and stuck on.

resistor.

Please see my tip at http://www.fixya.com/cars/r6234839-doesn_t_heater_or_air_conditioner_blow . These are generic instructions. If you get stuck or need specific instructions for your car, please get back to me with model, year and engine info.

it could be the motor itself, the blower motor resistor or the heater switch. if you can jump the motor with a power source, you will find if its working or not, then if its good try the switch. the resistor generally will allow one speed to work, so try all speeds to rule that out.

it could be the blower motor resistor, this is what gives the motor different speeds, they are very common to burn out 1 or 2 speeds. They are not very expensive, I would look into that first

this problem is caused by a defective blower speed dropping resisitor, it is located right next to the blower motor.

you need to repace the bolwer motor resister,can't tell you where it is because all cars are different but am almost positive that this is what needs to be repaced.

You might have a bad speed selector switch, or your blower motor resistor is faulty.