To Furnace or not to Furnace...
Hi all, So my furnace was working perfectly fine except one or two times here and there it didn't light. I turned it off and back on and it lit just fine. The other night I came in and the blower was...
Forum Discussion
I wasn't entirely sure I understood what a sail switch is, even though I have repaired all aspects of RV's. Evidently I haven't worked on a sail switch!
So I did some searching to increase my own understanding of it and I found an article posted by somebody else on another forum I have never heard of.
So here is a copy of what they wrote in response to a similar question:
First, check the sail switch if you have one. The sail switch is an on/off device. (normally in the off position) It gets it's name from the "sail" or paddle that is attached to the switch mechanism. As the blower comes up to speed, it blows air onto the sail with enough force to push the switch closed, thus allowing electrical current to flow to the next component in line.
It's job is to determine if there is adequate air flow for proper combustion to take place. If the battery voltage is low or the fan does not come up to 75 per cent of it's design speed, the sail switch will not close.
Possible causes of this malfunction are: low battery, restricted return air inflow, restricted or inadequate outlet vents, restricted combustion air inlet or exhaust, faulty sail switch.
If the switch is ok, then check to see if there is a limit switch that might be interupting power to the circuit board. (some models allow the blower to run as a safety precaution even with power interrupted to the board)
Next, check for proper voltage at the circuit board. The circuit board will not receive power until the sail switch is closed by adequate air flow from the blower. The power must also flow through the limit switch.
When the circuit board is triggered by this current, it usually delays ignition for about 15 seconds to allow the blower to purge the combustion chamber of any unburned gases.
The circuit board then sends voltage to the ignitor assembly to ignite the gas/air mixture. At the same time, the circuit board sends power to open the gas valve(s) allowing the fuel to flow to the burner, after which, the circuit board monitors the burn cycle through a sensor that detects the presence of the flame. If the sensor does not detect a satisfactory flame within about 10 seconds, the board then shuts off the gas valves and discontinues the ignition spark. Depending on the board design, it will probably try for ignition up to three times. Beyond that point, it goes into lockout mode, will not retry for ignition until reset and the blower will continue to run.
If you have the correct at the circuit board, check for the correct voltage at the gas valve itself. If you show power and the valve is not allowing gas flow...replace the valve. If you don't have power at the valve...replace the circuit board.
So I did some searching to increase my own understanding of it and I found an article posted by somebody else on another forum I have never heard of.
So here is a copy of what they wrote in response to a similar question:
First, check the sail switch if you have one. The sail switch is an on/off device. (normally in the off position) It gets it's name from the "sail" or paddle that is attached to the switch mechanism. As the blower comes up to speed, it blows air onto the sail with enough force to push the switch closed, thus allowing electrical current to flow to the next component in line.
It's job is to determine if there is adequate air flow for proper combustion to take place. If the battery voltage is low or the fan does not come up to 75 per cent of it's design speed, the sail switch will not close.
Possible causes of this malfunction are: low battery, restricted return air inflow, restricted or inadequate outlet vents, restricted combustion air inlet or exhaust, faulty sail switch.
If the switch is ok, then check to see if there is a limit switch that might be interupting power to the circuit board. (some models allow the blower to run as a safety precaution even with power interrupted to the board)
Next, check for proper voltage at the circuit board. The circuit board will not receive power until the sail switch is closed by adequate air flow from the blower. The power must also flow through the limit switch.
When the circuit board is triggered by this current, it usually delays ignition for about 15 seconds to allow the blower to purge the combustion chamber of any unburned gases.
The circuit board then sends voltage to the ignitor assembly to ignite the gas/air mixture. At the same time, the circuit board sends power to open the gas valve(s) allowing the fuel to flow to the burner, after which, the circuit board monitors the burn cycle through a sensor that detects the presence of the flame. If the sensor does not detect a satisfactory flame within about 10 seconds, the board then shuts off the gas valves and discontinues the ignition spark. Depending on the board design, it will probably try for ignition up to three times. Beyond that point, it goes into lockout mode, will not retry for ignition until reset and the blower will continue to run.
If you have the correct at the circuit board, check for the correct voltage at the gas valve itself. If you show power and the valve is not allowing gas flow...replace the valve. If you don't have power at the valve...replace the circuit board.
