Best to replace the fuse as mentioned.

Please note that the system will stop working in the event of excessive heat at the blower control unit AND/OR a short circuit. It will resume operation if/when these are no longer factors.

If you still have problems look for a three wire harness and connector with the engine hood fully raised, look directly behind the brake booster near the top of the firewall. You will see the black connector with three wires, Red, Black, and Yellow. Disconnect the connector, it can only go back on one way. Note the wire colours to the respective terminals.

You will need a voltmeter for this test. With the engine running and temp wheel at max, fan speed on low, check voltage at the connector terminals NOT at the wires from the connector to the engine compartment.

You should have 12 volts between the red wire + and the Black (ground) - Terminals.
You should have about 1 volt at the yellow wire terminal + to Black (ground)- terminal. (Note that the fan will not run as it will be diconnected at the firewall)

Now push the Auto fan speed button. You should now have about 1.4 to 4.5 volts at the yellow wire terminal + and ground.

Now push the high fan speed button, you should now have between 6 to 9 volts at the yellow wire terminal + and ground.

If you find these readings your pushbutton assembly is OK and the problem may be the blower regulator or excessive build up of dirt and junk at the intake of the evaperator causing the blower regulator to over heat.

If this is the case you will have to remove the blower and regulator to inspect and clean the exterior of the evaporator coils.

Sorry but I don't have my notes or diagram with me.
Let us know what you find.
Acky