Other antiquated combo permutations that date back to the 1970s include a combination heater/stove/oven, (Duette), and a heater/water heater amalgamation, (Thermal Twin); both nightmares to service because of their compactness and individual quirkiness. I’m sure the younger RV technicians today are dumbfounded when one of these old combo units rolls into the service bay!
Today’s larger rigs can enjoy never-ending hot water and multiple heating zones provided by hydronic heating units. Hydronic heating systems provide a continuous supply of hot water for the fresh plumbing system plus comfort heat for the interior. Employing a diesel-fired burner, (Aqua Hot units), or a propane burner, (Precision Temp units), combined with 120-volt AC heating elements, these types of “on-demand” systems are much appreciated and handy for those slightly chilly mornings. The diesel or propane burner can be bypassed using heat supplied by an electric heating element, thereby conserving on-board fuel.
From a comprehensive annual maintenance standpoint, a detailed furnace clean and service procedure involves removal from the coach, partial or complete disassembly, new gaskets and a full bench evaluation; all outside the realm of the typical RVer.
(See, Beyond the Scope)
In addition, a three-fold testing process of the main propane pressure regulator and distribution system (including setting the correct delivery line pressure) is also performed by the pros. But from a user’s standpoint, there are tasks the average RV handyperson can perform that will be most advantageous to preserving the integrity of the RV heating system. Four key areas come to the fore:
In a normal sequence, the spinning of the main blower wheel closes a device called a sail switch, (so named since this small electrical switch is outfitted with a large “sail” or paddle that catches the air moved by the blower wheel). Even though adjusting the wall thermostat actually initiates the heating cycle, it’s the closing of the sail switch that starts the internal electrical sequence of furnace operation.
If the blower wheel is weighted down with excess dust and lint, (see photo), it will not spin fast enough to close the sail switch (also called an “air prover” switch, by the way). It “proves” the fan is spinning fast enough, bringing in enough air to support combustion. Too much weight, the slower the spin; the slower the spin, the sail switch does not close. An open sail switch; the furnace fails to ignite.
If you have compressed air available, while vacuuming, blow out all internal sections of the furnace. Be sure to wear the appropriate eye protection, as dust and dirt will certainly be blown about. The goal is to keep the insides of the furnace assembly as clean as possible. Wipe all surfaces down with a damp shop rag.
If the wall thermostat is the older mechanical type, it is still possible to clean and preserve the contact points as you would the circuit board above. There are multitudes of these simple, bi-metallic types out there. If yours looks the one in the photo, it will be necessary to remove the clear plastic cover to expose the two contact points.
Cleanliness of the warm air ducting is also crucial. Some heating systems incorporate a central, manifold ducting system either in the floor or the ceiling. Others simply have individual ducts running above the floor, under cabinets, through partition walls to each major section of the coach. Regardless of the type of delivery ducting in your rig, remove each register and vacuum as far into each duct as possible. Take care not to rip or tear the 4-inch round flexible ducting, if so equipped. The duct in this photo, discovered during an annually cleaning procedure, turned out to be the perfect location for mice to nest! Not only a fire hazard, it certainly contributed to erratic furnace operation.
In this photo it appears the furnace compartment door is cut too short. Actually, the decorative grill work restricted the return air flow (reducing the number of square inches through the door), to the extent that this gap below the door was necessary to bring it back within spec.
So as the approaching fall months lure us out to see the beauty, proactive coach owners will be diligent about having clean heating system components. They will also maintain a healthy battery system in order to power the furnace properly. Additionally, they will have inspected their ductwork for obstructions. And you know they will certainly not store cargo in the furnace compartment or otherwise block the path of return air.