Heater (and a/c) blower motor runs only at the two highest speeds

Your year--make--model didn't post for some reason? That info would help.
I'd have to check voltage and ground at the blower motor wiring connector when problem is ongoing. Maybe a faulty blower motor? If it works good on high-speed, hi speed doesn't use a resistor, the lower speeds do. Usually with newer vehicles it doesn't say, resistor, probably says, blower speed control module, or something like that.

A heater blower motor resistor is an electronic device with three or more progressive resistors that allow the heater blower motor to operate at slower speeds. The highest speed of the heater blower motor is not controlled by the resistor, so when the resistor fails, the fan will often work on the highest speed setting, but not the lower speeds.
To resistor is generally located under the dashboard and under the hood, near the blower motor . The resistor's electrical connector is disconnected, the resistor is removed and the new resistor is installed. On some vehicles it may be easily accessible, and on others it may take partial dashboard removal to replace the resistor.
Look under the hood, generally the wiring for the Blower resistor is attached to the wiring to the blower motor itself
It's inboard & below the motor, near the accumulator. You can see it standing beside the passenger fender. it's the off-white connector behind the L heater hose above the vacuum reservoir & the white WARNING sticker

The resistor is most likely bad but should still work on the highest setting.Would check pigtails to the resistor and to the blower motor for burnt or discolored wiring.You can try tapping the blower motor and wiggling the wiring harness too see if it will work on the highest setting. It is possible that the blower motor is bad as well typically when you lose the speed selection it is the resistor but you should always have high speed.

Having the year, make, model, and engine size would help.

But generally when this occurs it is a bad motor resistor. The resistor uses a set of resistors in series to drop voltage to control blower speed. The lowest setting uses all the resistors and the setting below high speed uses on resistor. Since none of the lower speeds work either the resistor for the setting just below high is burned out or the internal fuse has blown. Replacing the blower motor resistor should take care of the problem.



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hte blower resistor is shot, near the blower motor, have the blower motor checked my guess is that it requiring too much power to run, hence the blown fuse

sounds to me like you have a resistance switch problem. The old cars had springs, i. e. resistors to control the speed of the motor. newer vehicles have electronic controlers, they can be very sensitive to corosion. first check the plug the replace the switch.

The switch that runs the blower motor for air and heat sends the DC voltage through some big resisters when it isn't set on high. (On high it sends all the power to the motor.)
If the lowest speed doesn't work then one of the resisters has gone bad, or come disconnected. If more than 1 speed doesn't work then a differant resister has gone bad or disconnected. The power runs through each resister in series so the most common one to go bad is the second to highest speed. when this resister is bad thaen it will only work on the highest setting. Replacing the switch won't fix it. You will have to find the resister that is bad and replace it.
The resister bank is usually tucked up behind the dash where only a kid can focus his eyes, and contort himself enough to see it.
Once the resister is replaced it should run perfectly.
Presto.

The switch that runs the blower motor for air and heat sends the DC voltage through some big resisters when it isn't set on high. (On high it sends all the power to the motor.)
If the lowest speed doesn't work then one of the resisters has gone bad, or come disconnected. If more than 1 speed doesn't work then a differant resister has gone bad or disconnected. The power runs through each resister in series so the most common one to go bad is the second to highest speed. when this resister is bad thaen it will only work on the highest setting. Replacing the switch won't fix it. You will have to find the resister that is bad and replace it.
The resister bank is usually tucked up behind the dash where only a kid can focus his eyes, and contort himself enough to see it.
Once the resister is replaced it should run perfectly.
Presto.

Usually when the blower fan only operates on hi speed, its because of a failed blower motor resistor. You still have hi speed because on hi, the power going to the blower motor goes directly to it, as opposed to the lower speeds, when the power is routed through the resistor, thus lowering the voltage, which in turn lowers the speed of the fan. The resistor is usually located near the blower motor itself, under the hood back near the firewall.

replace switch, works 9 times out of 9.