I have a 2001 checy cavalier and the heater/air conditioning unit only works on the high setting, the fan does not seem to blow on levels 1-3 but works on level 4, Any thoughts on what is wrong?

it sounds like the blower motor resistor is burnt.
look under dash, behind glove box, you'll see the blower motor, just to the left of it you'll see a connector with about 6 wires on it, that is the resistor.
it has 2 screws that holds it in the haeter housing.
you can remove it and see if the resistors are burnt, if so helpace it.
if not let us know and we'll walk you thru the test porc. for it.
it's the cause for only high speed mode about 99% of the time.

you can also get a pic of at autozone.com
you'll have to sing up, log in, pick part, then when the part and price page comes up, look to right colunm of page and click on service/part explosion.
let us know how you make out.

Most likely it's a bad blower motor resistor.

In most cases when the blower only works on high I would agree that it is usually the blower motor resistor. Further testing will be required to be sure it is not the switch.

This post is old, so......

How did it turn out chubby?

replace that resistor yet?