After changing the duck bills everything is working fine except the pump runs every 30 minutes for 5-6 seconds. I've tightened all hose connections and don't find anything loose. It did this before changing the duck bills. Called Dometic and the girl recommended changing the vacuum switch kit pn 385310540. Does that sound right?
I had the exact same issue last week and I was told the same thing however I took the switch kit off and cleaned it and adjusted the pressure on the spring and it works fine now
Yep, your stuff is dirty (imagine that), clean the switch push rod and seal. Maybe back down on the low pressure adjustment a bit also. Remember, I'm an expert, it's in my name...
Before doing any of this, let it build up pressure, shut the breaker off. Try flushing it 15 minutes later and see if it still has a good amount of vaccuum. If it does it's probably the vaccuum switch, if not it's possible the hose going from the toilet to the pump is bad and has a small hole in it, or a broken fitting at either end.
Is your vacuum generator running and turning itself off? Not cycling on and off frequently? There was a fine adjustment on some of the older switches. At extremes adjustment, you probably would not notice a difference. I'm sure this is not your issue. Lets make sure all is working correctly before we blame a pressure (expen$ive) switch. How old of a system. Service history? very little vacuum Compared to it working last month or to other boats? Flushing at all? Tell us about the vacuum pump; installed by itself with a mini torpedo bottle towards the head? Or the vacuum pump on top of a frosted white tank? The more info you can offer, the better we can help. ,rc