By “RV Doctor” Gary Bunzer
Water Pump Won’t Shut Off
Dear RV Doctor:
Something is wrong with my three-way water pump system. The pump will not turn off at any of the switches. The green light goes out when I push a switch, but as soon as a sink faucet demands water, the light comes back on and the pump comes on. I’m trying to figure out how to shut off the pump and how the switches are wired.
Robert Meeker
Via email
Some multiswitch configurations employ relays and electronic controllers, but if your setup is simply hardwired using manual switches, the following information may help.
Three-way switches can indeed be confusing. The important thing to remember: In order to have three locations to turn the water pump on and off, it takes two three-way switches and one four-way switch.
The accompanying diagram may help clarify. Note that only the “hot” wire is routed through the switches. The ground or negative battery conductor is not switched. The pump is simply grounded to the frame or to a ground lug somewhere within the system.
You’ll have to remove each of the three switches from their mounting in order to measure for voltage coming in and going out of each switch contact. And there’s likely no logic in figuring out which switch, in which location, corresponds to the diagram. Just realize that the four-way switch must somehow be connected in between the two three-way switches. And ensure that all the connections are clean, dry, and tight.
Although it’s not a permanent solution, you can always pull the water pump fuse in order to deactivate all the water pump switches until you can figure out which switch may be the culprit.
DC Components Won’t Run
Dear RV Doctor:
I’m new to RVing and I’m having problems with my house electronics. We just spent four nights hooked up to 50 amps and everything was great. Two days after we returned home, nothing in the motorhome worked; no interior lights, water pump, thermostat, etc. What am I doing wrong? You will not only be helping our motorhome, but also our marriage.
Mike Newton
Via email
I’m told I’ve saved a few marriages over the years! Do not despair! You didn’t state what brand of motorhome you have, but I’d first check whether you have a battery disconnect switch in the coach. In other words, is the battery truly connected into the system? With the battery bank disconnected, it would not be producing output, nor would it be able to accept a charge from the battery charger in the coach. It would be totally isolated from the motorhome. Since you were connected to 50 amps AC power, the converter was likely powering all the 12-volt-DC equipment on board. So, check for an activated battery disconnect switch first.
After that, it would be a matter of determining whether the battery charger is charging the battery bank. Be sure to verify that all the battery-related fuses/breakers are functioning as well.
And, finally, it might be time to determine the health of the battery bank itself. How old are the batteries? Are they still viable?
If none of this pans out, send me the brand and model of the motorhome, as well as detailed information about the charging device in the coach, the converter/charger or inverter/charger. I’ll need a little more information to dig deeper. Now, take your wife out to a nice restaurant and tell her you’re working on the problem.
Cannot Cool The Motorhome
Dear RV Doctor:
I purchased a new 2016 motorhome and I don’t think the air conditioner is cooling properly. What differential should I expect between the outside and the inside temperatures? All the shades are closed, and the insulating vent pillows are installed.
Gene Eichelman
Via email
That temperature differential is called the Delta T. It’s not so much the difference between outside and inside air temperatures, but rather the difference between the cold air coming out of the ducts compared to the warmer air flowing back through the return air grille to the air conditioner. It compares the temperature on each side of the evaporator. An average RV handyman can check it with relative ease using nothing more than an inexpensive probe-type pocket thermometer. The goal isn’t so much a pinpoint, accurate reading, but rather a method of obtaining the difference in temperature readings between the cold air produced and the return air.
To obtain the difference in temperature readings, begin by running the air conditioner on “high” for a minimum of 30 minutes. Be sure all the windows and vents are closed and all air conditioner ducts are open. Position the thermometer directly in the flow of the cool air being discharged into the RV. After the temperature stabilizes, note the reading. Next, place the thermometer probe in the path of return air to the unit. The return air path is that path of air that goes directly through the filters. The probe actually can be inserted into the filter element. Note this reading as well.
On “high,” a temperature differential of 18 to 22 degrees Fahrenheit indicates a system with the proper charge of refrigerant. In areas of high humidity, however, the temperature differential may be somewhat less.
Also realize an RV air conditioner can reduce the ambient temperature only by this approximate differential. If it’s 105 outside, you’ll be fortunate to obtain an inside comfort level around 85 degrees. Because of their relative size and capacity, most RV air conditioners are simply no match for extremely high temperatures. That’s why you’ll see two, three, or more units on larger coaches.
If the Delta T you measure is substantially less than 20 degrees, contact your local RV service facility; further troubleshooting is required. There may be a slow refrigerant leak somewhere in the closed system, or a faulty component may have reduced the overall cooling efficiency.
Though RV owners can safely perform basic rooftop air conditioner maintenance, repairs should be handled professionally. And in most cases, it will likely be less expensive to just replace the air conditioner than to repair it.