By “RV Doctor” Gary Bunzer
Chunky Carbon
Dear RV Doctor:
On my older Dometic RM3801 absorption refrigerator, a buildup of carbon causes the spark electrode to ground out. The carbon forms a bridge that connects the ignitor and the thermocouple, which prevents the ignitor from restarting. I thought this issue, which began a couple of years ago, might be linked to something in the propane, but I use the same propane for other appliances with no problems. I am stumped. Any ideas?
Brad Townsend, F368128
Hanover, Maine
Looking at the photo you sent (left), I think that piece of carbon fell from inside the cooling unit’s flue pipe. It’s very common for carbon to accumulate inside the flue pipe and on the flue baffle inside. Simply driving down the road can loosen large pieces that just fall straight down onto the burner assembly.
To start, I’d suggest a deep cleaning and servicing of the refrigerator as well as testing and adjusting the propane regulator. We can’t rule out a fuel mixture issue, even though the other appliances seemingly operate just fine.
To clean the flue, technicians use a special flue brush to scrape away the buildup inside. The baffle must be removed and cleaned as well. I recommend doing this service each camping season, but because of the complexity of the task (often the refrigerator must be removed) and the use of specialty tools, a certified technician should perform the cleaning and servicing. Even if you can periodically clean the burner and the orifice and brighten the thermocouple yourself, adjusting the regulator and testing the gas valve should be left to the pros.
If the gas pressure is spot-on and the air mixture is correct at the burner, it’s possible the baffle is simply not drafting properly. It may not be positioned correctly, or the flue cap might be improperly installed or even missing. Are you able to inspect the flue cap near the top of the cooling unit? Depending on the installation, it may be necessary to remove the roof vent to gain access. The flue cap or an improperly positioned baffle could be causing the incomplete combustion. But remember, this assumes the gas pressure is right at 11.0 water column inches and the orifice is clean.
Where’s The Wiring?
Dear RV Doctor:
How do you determine whether an RV is prewired for an additional roof-mounted air conditioner? My coach has 50-amp service, but I have no idea how to find the wiring for an additional unit.
John Lesser
Via Email
Typically, when an RV is prewired for a second air conditioner, manufacturers either place a sticker on the ceiling near a mounted 14-inch roof vent indicating the location of the wiring, or they install a junction box in the ceiling with the prerun Romex cable capped off. You also can remove the ceiling bezel/trim for that vent from the interior and look at all four sides of the rough opening for a drilled hole containing the wiring.
Another clue would be the presence of an extra 20-amp circuit breaker in the panelboard breaker box. And yet another option would be to call the manufacturer and provide the VIN for your motorhome. They should be able to look up the build sheet and verify whether that coach was prewired for another air conditioner. And even if it is not prewired, a competent service tech can install a second air conditioner, assuming there is an open circuit breaker position at the breaker box.
Stuck Termination Valve
Dear RV Doctor:
Help! We need to know how to repair a stuck P-trap. We believe the pull lever is broken. Unfortunately, we are unable to move the coach, as it is currently being winterized. Basically, we need to know how to get to the trap so maybe we can manually open it.
Nicky Myers
Via Email
I think you are confusing a broken termination valve, or dump valve, with a P-trap. P-traps are located under each sink in the motorhome and do not have a pull lever.
If you cannot move the coach, first you’ll have to locate a company that offers a dumper/pumper evacuation service. Pumper trucks, otherwise known as honey-buckets, hopefully will be able to evacuate the tank through the toilet. This operation must be performed with care, so as not to collapse the holding tank with too much suction.
Then, find a mobile RV technician to replace that dump valve. Most mobile techs will not be equipped to evacuate the tank but are able to replace the valve once the tank is emptied.
With the T-handle broken off and the tank valve stuck closed, the only other option is to remove the valve itself. There is no manual override to open the valve if the handle or cable has become disabled. That T-handle IS the manual method. Four bolts sandwich the valve between two adapters in the waste plumbing system. Remove those bolts and the valve can be removed, but keep in mind that everything in the holding tank will empty onto the ground! That’s why you need a honey-bucket service.
I would recommend installing an electric gate valve instead of another manual valve. Electric gate valves open with the push of a button, and they DO have a manual override. In my opinion, that would be your best option.
Waste Management Redux
Dear RV Doctor:
I read about a kit from Drain Master that can permanently connect the sewer hose to the holding tanks, so all that’s needed when dumping is to put the hose in the sewer inlet and open the nozzle valve. This seems like a no-brainer, and I am wondering why RV manufacturers don’t do it. What’s the downside?
Rusty Austin
Via Email
That’s exactly what I’ve been wondering for a few years now. In my opinion, the two main factors are 1) the RV industry is reluctant to change, and 2) the system will cost a little more for the manufacturer. But they’ll readily make up for the cost with reduced warranty claims, especially if they pass that extra cost down to the RV owner, as is typical.
The RVers I’ve spoken to would gladly pay extra for a system that minimizes the most displeasing aspect of motorhome ownership. However, great strides have been made, and I feel that within another few years, the Drain Master/Waste Master system will become mainstream. All it takes is for one major manufacturer to make the leap. Look what happened when Newmar produced the first motorhome with a slideout! Now try to find any coach without one!
It may also take some pressure from motorhome owners to convince that first manufacturer. Feel free to write to your favorite maker and request they install the ultimate waste management system. It is available, just not from the factory yet.