My Chevy 2007 HHR heater only works on high. How do I fix it and what do I need?

Maybe problem with blower motor resistor? Hi speed doesn't use a resistor, the lower speeds do. It shows to be behind the glove box.

A blower motor that only works on high likely has a bad resistor pack. The resistor pack limits current to the blower motor for any setting other than high. When the selector switch is set to high, direct voltage is applied to the motor bypassing the resistor pack. A resistor pack costs about $30 to $35. A plugs into the wire harness for the blower motor. You only need basic tools to switch it out. Google your year, make, and model to see where yours is located. (They are usually on top of or very close to the blower motor.)