why does heater/ac fan not come on at times. Am perplexed. not best time of year on 2001 Cadillac DeVille DTS

one day we drive and the heater works fine, next time, nothing.

Asked by for the 2001 Cadillac DeVille DTS
I had the same trouble it would sometime go on and off when I hit a bump. Turned out to be the blower motor located under the dash on the passenger side (after you remove some panels etc.) Good luck