Heater blower switch only works on high

on high ?
bad fuses
Hi works, and others speeds dont, bad switch or blower resistor bad.
hot wire the blower motor , does it work now. bingo, bad controls.

Blower resistor is bad . Do you know what that is ?
Jeep Cherokee Blower Motor Resistor Replacement

This is 100% the Blower (Fan) Motor Resistor located near the Blower Motor.
This is a very common problem with Chyrsler, Dodge, Jeep and Plymouth. The key symptom is the Fan only working on High.
This is very easy to access and replace.

Let me know if this helped....

They are near the blower motor as the air is used to cool the resister, usually on the bottom of the blower housing.

Yes I would go with the switch, BUT, does it have a resistor bank? That is, how does it reduce the speed? Many systems use resistors to lower the speed. Burnt or bad connections can cause this as well.
You can test the blower motor by connecting direct power from a source like the cigarette lighter if you are handy.
Most of the time the lower speeds konk out but the high speed continues to work this is the resistor bank that goes out.

If the heater only works on the high setting, your problem is the heater fan resistor, not the relay.

qss

you need to change the resister block for the fan. it is located on the heater duct near the fan... there is a connector on it and two or three screws holding it in.

Robert

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Check it with a test light or Multimeter for power to blower motor first, with switch on high. If no power to motor, problem is elsewhere. Here's a link that will help you. Click on the pictures to expand.

http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528008ac7f

Check the blower motor resistor, I,m not sure where it is located on your vehicle most are on the firewall under the hood.