1990 240 Blower Fan Only Works When In "OFF" Position & A/C Turned On

[kblupino]

I'm experiencing a problem that I haven't seen posted elsewhere else. I've got a 1990 245 with factory A/C and the blower fan has five positions: Off - 1 - 2 - 3 - 4.

The fan now only blows when the fan switch is in the "Off" position and the A/C is turned on. If the fan switch is then moved to any of the 1, 2, 3, or 4 positions, the fan stops blowing (I know that the fan is supposed to blow in the "Off" position when the A/C is on in order to help evaporate moisture from the system so that function is normal).

When the A/C is turned off, the fan does not blow regardless of the switch position, even in "Off".

There was no rattling, buzzing, or other indication that the fan was failing prior to this failure mode. It happened while the fan was operating normally (I don't remember what speed setting it was on) with the A/C on.

All of the posts I read about the resistor pack failing say that the fan continues to run when in the 3 or 4 position, but that's not happening here. Could it still be the resistor pack? Any insights or help is appreciated!

[volvolugnut]

I think the switch contacts may be bad or dirty. Remove, inspect and clean.
volvolugnut

[kblupino]

Turns out fuse 3 was blown, which is for the blower switch. I replaced it and now it works again.