Four trips. Long time client called now and again saying that once in awhile the blower would start making all kinds of racket for a short time and go away. It only would happen on cooling or when she switched to fan on. This was before fan on powered a third choice in speeds.
Three times I go or stop on the way to other calls and nothing and nothing to even consider would be causing it. I told her if just once I can get over and actually hear the problem I will know for sure what it is.
Sure enough on the fourth trip the control board relay was freaking out powering the fan on and off about ten times a second before the fan caught and ran. First time I have seen this.