Please keep in mind when reading our tips, that due to liabilities, Mobuilt RV Repair, is not liable for any damages that may occur by following any tips listed. Please remember these are only suggestions. Following these RV tips is at your own risk. Thank you for understanding.

Furnace Maintenance

Is it that time of year again?

When Fall is here and the cool days and crisp nights remind us that now is the perfect time to think about your motor home's furnace.

Furnaces for recreational vehicles are designed differently from most furnaces designed for residential use. The furnaces installed on Winnebago Industries' motor homes are classified as "forced draft furnaces." The operation of the furnace is controlled through the 12-volt thermostat. When the thermostat is set above the current room above the current room temperature, the contacts inside the thermostat close, allowing current to flow to the limit switch and time delay. As the 12-volt current passes through the coil of the time delay relay, the contacts on the relay close, completing a circuit to the motor and the motor comes on. The purpose of the time delay relay is to provide a means of controlling the blower operation on initial startup and after the thermostat is satisfied. When the thermostat contacts open, the circuit through the coil of the time delay is broken but the fan blower motor continues to run until the time delay relay contacts open after approximately 3-5 minutes. As the motor reaches approximately 75 percent of its normal rpm, the air-flow generated by the room air pushes against the paddle on the sail switch (sometimes referred to as a micro switch), closing its contacts. (NOTE: A low voltage power supply will not provide sufficient motor rpm to engage the sail switch.) This allows current to pass the high temperature limit switch. If the limit switch is heated to a pre-set value, the internal contacts will open, preventing current from flowing through the switch. The module board receives 12-volt current after it passes through the limit switch. After a 12-18 second delay, current will pass through the module board to the gas solenoid valve. The current to the valve opens it and allows gas to pass to the main burner. Simultaneously, the module board sends high-voltage current through the electrode wire to the ignition/flame sense electrode. The voltage seeks a ground between the electrode and the ground probe and a spark occurs. The spark then ignites the main burner. The module board also performs the lockout function. "Lockout" is a term used to define a safety feature in which the furnace controls air rendered inoperable to prevent the furnace from operating. This occurs when the burner fails to properly light or stay lit when the thermostat is calling for heat. The module board monitors the burner activity by utilizing a flame sensing circuit which senses the presence of main burner flame. If the proper flame sensing is not obtained or if the burner fails to light (on certain models after the third attempt), the furnace must go into 100 percent lockout. When lockout occurs, the spark stops, the voltage from the module board to the gas valve is discontinued, and the valve closes. The unit will remain in lockout and the blower will continue to run until the thermostat is turned off. Reignition will not occur automatically. If it could, there would not be a 100 percent lockout. Turning the thermostat off disengages the lockout function of the module board. After the blower has stopped, the ignition sequence can be started again.

CAUTION: The lockout function is a safety feature of the furnace. If a furnace has repeated or continuous lockout occurrences, you should obtain service from an authorized repair center.

Preventive maintenance is essential to reliable, safe operation of the furnace. By far, the two most important areas to watch closely in order to assure safe, reliable operation are the venting and the main burner.

Furnace maintenance and inspection are not do-it-yourself projects and should be performed only by qualified service technicians. You should have your furnace inspected by a qualified dealership technician twice a year and at any time there appears to be a possible problem.

RV Forced Air Furnaces

      The air intakes (for the fan that supplies return air to the furnace blower) are located on either side and the top of the metal furnace housing. These air intake slots draw air from the surrounding area and the blower fan forces this air past the sealed combustion chamber in the furnace and on to the warm air duct work.

      If this intake air flow is restricted, (with loose plastic bags, aforementioned cookie sheets, etc.) the fan motor speeds up. (the same effect is observed when the intake hose of a vacuum cleaner is plugged off).

      There is a separate combustion air system, sealed from the inside of the coach, that feeds fresh air to the burner assembly inside the furnace. This system draws in outside air to allow the proper combustion of the fuel gas and then forces the exhaust products out again. The fan for this system is powered by the same furnace motor that runs the blower, there for it speeds up at the same rate.

      The increased air flow in the combustion chamber alters the burn characteristics of the flame - producing a leaner, hotter flame. This overheating can lead to failure of the furnace safety devices, damage to the electronic components of some models or in the worse case a cracked combustion chamber. Exhaust products, including CARBON MONOXIDE, will now be forced into the living area !!!! CO is odorless, colorless and extremely toxic - a silent killer.

      Please check your furnace compartment for air flow restrictions.

      If you have any doubts or concerns regarding your furnace's condition, have it inspected by a licensed, qualified RV gas technician.

      A carbon monoxide detector installed in your unit is a very inexpensive life insurance policy.