81 300TD Intermittent fan

Hello! I have a problem that seems to be getting worse over time: My fan doesn't always come on when I push the climate control buttons. I thought it was only in the hotter weather, but now the same thing is happening,
even though it's cooler. When the fan DOES work, it's strong on high and constant - no intermittency.
I can hear the vacuum working the valves when I press the buttons, so I think the controller is working. Any troubleshooting tips? Maybe a loose wire? How does one go about taking the controller out of the dash?
TIA
Tweaks
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Most likely is bad fan motor... next time it doesn't work... bang on the lower passenger side dash to see if it kick on.
Another possibility is ignition switch... if it doesn't work, try turning back the key but don't shut off engine... if fan comes on, then ignition switch is bad.
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Actually, that's one little bit of information I forgot to mention (sheepish grin)! The fan will sometimes (not usually, but sometimes) come on with the ignition switch turned on but the motor NOT started, but then goes off (and generally will not come back on again) when the motor is running.
So, you think this points to the ignition switch? That's pretty wild.
Thanks
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I would suspect the switch at this time... then diagnose further if problem still exist...
You see...16 years is a long time for ignition switch...
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One last thing! I had several keys on the keyring, and, after taking them off, I was able to move the key somewhat and the fan works! So, that proves what the culprit is, I reckon.
Thanks for your help - I now have only the key on a detachable ring. Should have done that long ago.
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will do - looks like an inexpensive try. I experimented a bit with it when I got home, and, sure enough, the fan runs with the key "on", but as soon as I start the motor, nothing. I even tried it while driving ( I was fiddling with the key and the motor turned off) and the fan came on!
Very strange, but it would be good to have my AC back! Thanks.
tweaks
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will do - looks like an inexpensive try. I experimented a bit with it when I got home, and, sure enough, the fan runs with the key "on", but as soon as I start the motor, nothing. I even tried it while driving ( I was fiddling with the key and the motor turned off) and the fan came on!
Very strange, but it would be good to have my AC back! Thanks.
tweaks
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