I have a switch on the dash that is in series with the
pressure switch. When it is up on boost and the
pressure switch is fully engaged I can flick the dash switch back and forth and there is no chatter.
It was only when the
pressure switch was coming up to or down from full contact that I would get the chatter. It may be that as the
pressure switch begins to close/open that there is intermittent contact. The chatter was especially prevalent when the boost slowly went through the switch point. Sometimes I could get the relay to chatter for about a full second.
The capacitor took care of it. I tried to slowly go through the switch point and I did hear a couple of clicks, but noting like the chatter before.