Aircon/heater fan problem - '94 Jimmy

Looking for any helpful input on this problem with the fan for the heat/air in my '94 Jimmy. The fan is still working on the low setting, but there is usually no change when I move the switch to the higher fan settings. Occasionally it does work for a brief period of time, then cuts back to the lowest setting. I'm thinking it is a problem in the switch rather than the fan, since the fan still works. So my questions are:

If this is the switch, how difficult is it to get to and replace? If it is the fan, again, how difficult is this to get to and replace? Or, are there other things I should look at first.

The instrument cluster is the older type, not the digital display, if that makes any difference. Thanks in advance for any advice.
Dave

Check the resistor block.