1995 Geo Tracker fan speed problems

Hi everyone...

    I have a 1995 Geo Tracker and since its been getting a bit colder out, I
have to use the heater a bit more, and noticed that I have no fan speed on
the first two speeds, but it works fine on the higher settings.  Could this
be a switch problem?  How do I go about tracking this problem down?

Thanks in advance for any advise...

Fwed