How To Service An Rv Propane Furnace

A mouse nest tin can go a fire hazard if regular furnace maintenance is ignored.

Follow a few simple steps to keep your motorhome warm in winter.

Past Gary Bunzer
December 2015

Motorhome owners — especially those who embrace winter travel — should exist proactive in preparing the forced-air heating system for those days and nights when the thermometer dips.

An RV forced-air furnace is a sealed combustion system, and then information technology is relatively piece of cake for coach owners to perform a few maintenance procedures to ensure that warm air will circulate when needed. This is not to say the need for professional attending is eliminated altogether. Every bit with whatsoever propane-burning appliance, it is still vital that the delivery line pressure be measured and adjusted, the regulator be tested, and a deeper cleaning be performed periodically. As well, it is imperative that the consummate propane piping system be tested for leaks at to the lowest degree once per camping flavor.

Simply there are a few unproblematic steps all motorhome owners tin can follow to avoid shop labor costs. I've always maintained that the iv crucial areas regarding the RV forced-air furnace are equally follows:

Cleanliness of the furnace
Proper routing of the ductwork
Return airflow
DC voltage input

Everyone should carry a decent digital multimeter (DMM), a few paw tools, and standard cleaning supplies and then these four areas can be addressed before the onslaught of wintertime.

An important safety note: Coach owners should never remove any component on the sealed system that is held in place with a gasket. Breaking the seal on whatsoever gasket potentially can cause a unsafe carbon monoxide leak. Some of the aforementioned specific procedures are taught to professional person service technicians and require special diagnostic equipment not commonly carried by the average RV owner.

Furnace Cleanliness

Vacuum and wipe downwardly all portions of the furnace y'all can easily access. Though all forced-air furnaces are quite similar in their sequences of operation, they may exist assembled into many different configurations. Simply merely keeping the unit free of accumulated dust and dirt will help ensure proper operation.

Vacuum in and around all areas of the furnace compartment, including the floor ducts. In some cases, it may be possible to remove a front panel to gain admission to the interior portions of the furnace enclosure. In other cases, access may be gained through a panel from outside the motorhome. Use a soft, damp material to wipe down all metal components.

Take time to fully inspect the intake and frazzle vents on the exterior of the motorhome. The fireside stories you've heard of wasps, spiders, mud daubers, and birds possibly building a nest inside that intake/frazzle assembly are truthful. Obstructions in the intake tube will crusade an overly rich mixture at the burner, resulting in incomplete combustion. Obstructions in the frazzle tube can be a fire hazard. Neither state of affairs is skillful for yous, the furnace, or the motorhome.

Ductwork Routing

Much of this section pertains to coaches equipped with flexible runs of ducting rather than motorhomes built with rigid in-floor ductwork. About flex ducts are routed in a higher place the floor, inside cabinets, under sofas, etc. Inspect the routing of every run, since they're usually easily accessible. Look for extended runs and collapsed or pinched ducts. Longer-than-necessary branch ducts sometimes can be shortened to eliminate heat buildup. Excessive estrus can cause the furnace to brusk bicycle. Every bit noted in a higher place, try to vacuum or wipe away dirt or dust inside each duct as far equally yous can reach.

Inspect all adaptable estrus outlet registers, making sure most of them are fully open. The number of ducts routed throughout the jitney is determined by the Btu rating of the furnace. In order for the furnace to operate properly, a certain number of ducts must be connected to its plenum or manifold. If as well many of those ducts are airtight (or not enough ducts are installed), the chance of a short-cycling sequence increases.

Render Airflow

For proper operation, all forced-air furnaces require that a specific corporeality of fresh air be returned to the furnace enclosure. This is achieved through a grille or a set of louvers mounted somewhere within the motorhome's living space. Practise non cake or modify this grille in whatever style. Some coach owners accept unwittingly installed a filter of some sort within this grille. Doing so will cause furnace issues. Be certain the return grille and the area immediately behind it are free and articulate of obstacles.

Likewise, the casing of the furnace also contains stamped cutouts in its beat that represent with the minimum render-air requirements, and these openings also must remain clear of obstructions. Instances of faulty furnace functioning have been caused by something only falling out of a drawer or being blimp under a cabinet and onto those vent openings, thereby blocking the flow of render air to the furnace. Audit under the cabinet for anything that may have fallen on the furnace enclosure mounted below.

DC Voltage Supply

Of all the maintenance items a motorhome owner can perform, maintaining a healthy battery system is loftier on the list. The proper amount of DC voltage is crucial to the safe and efficient operation of the forced-air furnace.

Near modern furnaces operate at a voltage input between x.v and thirteen.5 volts DC. Of course, 10.5 volts is basically a expressionless battery (100 percentage depth of discharge), so more than probable, the conscientious RVer will keep the battery bank at a higher level of charge. I stress the fifty percentage rule; never belch to beneath 50 pct of capacity, unless necessary. But it'south not uncommon for a somewhat-depleted battery to provide less-than-sufficient voltage, especially during a dry camping attempt. Low voltage causes the blower cycle to spin slower, peradventure too slow to properly close the sail switch. The canvass switch initiates the heating cycle by powering the circuit lath, which in turn opens the gas valve and creates the spark that ignites the main burner.

On the flip side, likewise-high voltage coming into the furnace also tin crusade issues. Never power the furnace straight from a battery-charging device, converter, or off-line power supply. The incoming voltage must be "filtered" somewhat. This is accomplished by connecting the furnace to a bombardment excursion within the motorhome. Maintaining a clean, properly charged battery bank is essential for optimum operation of the furnace.

Propane Fuel Supply

During winter RVing, ever go along the propane container every bit total as possible. Here'due south why. The liquid fuel in the propane container is warmed by its contact with the external walls of the container, which in turn is warmed by the ambient air around it. That means the container's interior wall surface must be sufficiently "wetted" by its contact with the liquefied propane to vaporize at a rate greater than what the appliances demand at any given fourth dimension. Remember, propane is stored as a liquid simply burns as a gas. The total charge per unit of vaporization is adamant by the temperature of the liquefied propane coupled with the amount of surface area wetted past the propane. This is non an issue during the warm summertime months, but it can crusade consternation during winter travel.

In very cold climates, it'south entirely possible that the motorhome appliances (especially the fuel-hungry furnace) will demand and outrun the charge per unit of vaporization as provided past the propane container. The result is that some appliances only shut downward of a sudden, just as though the container were out of fuel. Some ASME tanks are more prone to this but because of their physical design, so keep that propane fuel topped off during the cold winter months.

Summary

Serious and seasoned coach owners understand the importance of proper preventive maintenance. Following these few quick and like shooting fish in a barrel procedures will give your heating organization an advantage in the cooler months. Merely I must over again offer a reminder about the importance of a thorough cleaning of the burner orifices (to remove carbon deposits); correct gap spacing of the electrode assembly; and complete testing of the force per unit area regulator and the unabridged piping organisation. And for those tasks, rely on certified RV service technicians.

Remember, RVing is more than than a hobby; information technology'southward a lifestyle!

Furnace Operating Sequence

Understanding a furnace's sequence of functioning tin exist helpful when troubleshooting. The following data pertains to a Suburban Manufacturing Company 12-volt furnace:

The wall thermostat controls the performance of the furnace past reacting to room temperature. This allows current to flow through the ON/OFF switch to the module board.

The module board constantly checks for a minimum of 9.5 volts. If in that location is non nine.5 volts, the module lath will go into a standby manner until acceptable power is supplied. It will then resume normal operation.

Upon a telephone call from the thermostat, the module board thermostat circuit will go active. The sail switch excursion is verified as existence open. The blower output is energized. The blower motor starts.
The module board will then verify that the sail switch circuit is airtight and the motor is upward to speed. If this excursion remains open for 30 seconds later on the blower motor starts, the module board will become into lockout manner and close downwardly the blower motor.

The module board checks that the gas valve relay contacts (which are located on the module lath) are open before the ignition sequence starts.

The board has a pre-purge timing circuit of approximately 15 seconds. This allows the combustion chamber to purge.

The module board will energize the gas valve and enable the high-voltage spark output to the electrode for seven seconds of ignition fourth dimension.

The module board will and so check for flame sense to verify successful lighting of the main burner flame. Sparking of the igniter volition then exist terminated and the gas valve and blower outputs will remain energized.

If ignition is successful, the module board will monitor the flame sense, sail switch and limit switch circuits, and the thermostat inputs during the heating flow.

The flame is sensed through the spark wire and electrode. Therefore, information technology is essential that the electrode is properly positioned in the burner flame.

If the flame is not sensed after seven seconds, a 2nd fifteen-second purge cycle will brainstorm, followed by a 2d trial-for-ignition sequence. Afterwards three trial-for-ignition attempts with no ignition of the main burner, the module board will de-energize the gas valve immediately and the blower volition run for three minutes then shut down in lockdown style.

If during the heating cycle, the limit switch circuit opens and remains open up for v minutes, the module board volition go into lockout and shut down the blower motor. If this occurs, the thermostat will need to be reset for the furnace to operate.

When the thermostat has reached its set point and the demand for heat ends, the gas valve will be de-energized and the flame will go out. The postal service-purge flow of 90 seconds begins. When it times out, the blower motor output is removed, and the blower stops.