Mine quit working on speed 1 and 2. Now I only have auto and 3. Any ideas??

It is either the resistor pack, or the switch itself. I don't know nissans specifically enough to tell you how to find or check either though.

The blower is under the dash on the passenger side. I'm pretty sure the resistors are there as well. The fan cools the resistors, so they are in the same housing. Quite often it is a broken connection or burned-up connector.

On the main Forum directory, you will find the How To section. There are some articles with pictures that might help you out.