Burner Head, Electrode And Valve Assembly - Atwood AFS Series Training Manual

Burner Head, Electrode and Valve Assembly

itself. Therefore, when trouble-shooting a furnace problem, always check the following items before testing or replacing
components.
#1- Gas Pressure
The gas pressure should be set at a minimum of 11" W.C. with a minimum of 50% and ideally 100% of the gas fired appliances operating. You
should test this pressure with a U-tube Manometer only. If you choose to use a dial-type manometer, calibrate it often with a U-tube
manometer.
#2- Voltages
Voltage to the furnace should be between 10.5 and 13.5 VDC during operation with the interior lights ON and OFF. This check should be
made with the battery, converter or generator when applicable. Use a digital or analog multi meter when taking voltage readings. Do not use a
test light. It does not provide enough useful information for proper diagnosis.
#3- Ducting
Always make sure that the furnace has at least the minimum number of ducts (not including closeable outlets) called out in the installation
instructions. Check for proper duct connections at the furnace and heat registers, collapsed ducts and holes in the ducting. The duct runs must
be a straight and tight as possible. The heat ducts must also be clean and clear of obstructions.
#4- Return Air
The return air passage should meet the minimum square inches as specified for the particular model of furnace in the installation instructions.
This air passage should also be clean and clear of obstructions. Do not put air filters in this passage way. Also, make sure that combustibles
are not stored in the furnace compartment.
#1 – Gas Pressure
A furnace is a consumer's friend when the outside temperature gets colder. Unfortunately though, cold is an enemy of LP gas. The BTU
capacity of LP per volume decreases as the outside temperature gets colder. Therefore, based on how full the LP tanks are, the ambient
temperature outside and how many BTU's the furnace is, there may not be enough gas to sustain ignition on the furnace.
Using the charts below, let's say that a 40,000 BTU furnace won't fire we also know that the 65 lb. LP bottle on the RV is 40% full and it is 0°F
degrees outside. One's first thought might be that the burner or valve is bad. However, if we use the chart, the vaporization capacity of the
tank in these conditions is only 38,500 BTU's. The furnace is not going to perform very well because there is insufficient BTU capacity in the
tank. This make for a lean gas/air mixture which may not be able to be sense by the ignition control to maintain continuous operations.
If you were to put an insulated fire resistant blanket over the tanks and a 75 watt light bulb under that, you would probably raise the
temperature of the bottles 10-20°F degrees and almost double the BTU capacity of the tank to vaporize the propane for proper operation. So
keep in mind that a furnace problem is not always a component problem.
The burner head, electrode and gas valve on the late model 79 series furnaces are individually
accessible. However, to service these same components on the late model 85 and 89 series,
remove the complete assembly.
The different models and /or BTU ranges of furnaces use different burner heads. These burners
differ by the size of the top gas port holes or the deflector that runs through the throat of the
burner. If the wrong one is used, it may cause an ignition, sooting or flame sense problem.
When an electrode assembly is installed on a furnace, they will already be in a fixed and
predetermined position above the burner. The only adjustment that you may need to do is on
the sparking and ground electrode points. This gap should be 1/8". However, when the
porcelain on an electrode assembly becomes cracked, it will not function properly and will have
to be replaced. When doing so use the proper electrode assembly for the model of furnace
being serviced.
There are only two versions of the solenoid valve available for the models of furnaces noted
above. These two valves are identical except for the gas inlet porting on them (side or front). As
stated earlier in this manual through, the coils are what usually breakdown but they are easily
replaceable.
20 lb. Bottle (*30 lb. bottle multiply rate shown X 1.40)
40
The 4 Always
Remember that you are working
on a heating system and not just a
furnace. A majority of furnace
problems lie outside of the product