Vampires and multimeters

Sounds like we're making progress. Definitely seems like a pump problem. The pump will draw current proportional to the pressure it is pumping against. With a faucet open the pump should be running but the pressure is something less than the cutoff pressure. When you close the faucet the pump should continue to run, increasing the system pressure until the upper trip point is reached. The current will increase as the pressure builds until the upper trip point is reached and the pump is disconnected. If the pump is unable to reach that upper trip pressure it will continue to run forever. SO, in your 45 minute experiment did the pump continue to run or just stop, sit, and heat up? It sounds like the latter, in which case it will get hot and maybe seize up. The upper trip point may be set too high or the pump may be defective. The trip pressure is adjustable with an Allen wrench. In either case the 6A load you see will definitely drain your battery as you observed. Six Amps for 24 hours is 144 AH which is more than 50% of the rated battery capacity. It should lower the measured voltage to less than 12.0V. Truth is beginning to emerge from the smoke and clouds. 

The action of the LP detector sounds like low voltage. This could be a combination of weak/discharged battery and marginal wiring. We'll work that after we deal with the pump.

It does seem you have zeroed in on the problem. For some reason the pump cannot reach the upper trip setting of the pressure switch. I assume you get adequate flow when the faucet is open, indicating no obstructions in the intake such as the strainer. Either the pump itself is weak or defective or the cutout switch is set too high or defective. Determining which requires a pressure gauge on a faucet. The pressure switch, usually on top of the pump next to the power connection, is adjustable with an Allen wrench. Backing out the screw (CCW from the top) will decrease the cutoff pressure. Not knowing your exact camper I cannot help you much more. If the camper is still in warranty a dealer visit is in order. If not you might still take it by a dealer and have him test the pump assembly. Worst case a new pump a less than $100. 

The manual for my pump says adjusting the pressure switch should only be done by a qualified technician, so I think I have reached the limit of my capabilities (or at least my desire.) I made a service appointment with the dealer. The soonest they can get me in is three weeks away, but that's OK. At least they won't have to start at square one with only the symptom of "something's draining my battery" and for that I thank everyone on this board. I'll post an update when I find out what they had to do. THANKS to all for not giving up on me! I learned a ton and hopefully others will, too.

My guess is the pump is defective. Many RV pumps, like the ShurFlo series, are thermally protected. That means they will disconnect from the 12V source when they get too hot. When this occurs the input current will drop to zero. Until then the pump will continue to turn even if they can't reach the cutoff pressure. They should not seize up and not run. You should be able to hear and feel the pump running.

Be aware that dealers don't really know much but they want you to think they do. Their usual response is that everything is OK and please go away. Don't let them get away with that answer. You know there is something wrong with the pump and it probably needs replacing. Also be aware that, even though your camper may be out of warranty, many of the components carry longer manufacturer's warranties. Check it out in your manuals or on line.

Good luck and keep us informed. Your feedback helps us too

Originally posted by GLBCamper Final(?) battery vs. pump tests. I charged the batteries overnight and started this morning (after an hour for decay) @ 12.90. First test per Paul, check voltage at all pump stages: Switch on, no demand = 12.89 Faucet on it ticked down about 1/100th every few seconds to 12.78 until I shut off faucet, with the switch still on ("stalled?") it ticked back up at about the same rate, landing back at 12.90. I double checked the amp draw this morning and got the same results. Demand = 3.5, No demand = 6+. Also, even with a fully charged battery the LPGD light goes out when pump switch goes on. BUT does NOT when connected to shore power.