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Atwood Furnace Not Working


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My Atwood Furnace that supports the rear part of MH is not working.     The Front Atwood is working fine.  I swapped the boards out and move them from one side to the other and still nothing on the rear.   I Checked with my meter and the the main switch and fuse is working and the board is getting power.  I am thinking maybe a flow switch but do not know how to get to it as it appears it is on the back side of the motor?      Thoughts.

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14 hours ago, thancoc@bellsouth.net said:

My Atwood Furnace that supports the rear part of MH is not working.     The Front Atwood is working fine.  I swapped the boards out and move them from one side to the other and still nothing on the rear.   I Checked with my meter and the the main switch and fuse is working and the board is getting power.  I am thinking maybe a flow switch but do not know how to get to it as it appears it is on the back side of the motor?      Thoughts.

Does the fan run?

 

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A real quick walk through of what is supposed to happen:

0. We're sitting here with a tank with LP in it, and 12 volts making it from the battery through the fuse to the furnace and the thermostat happily showing numbers that say it's healthy and ready to server.

1. Thermostat decides it's colder than what you told it you like and sends control signal asking for heat. The thermostat does this by sending 12 volts to the furnace to signal it to wake up and do its job. This signal voltage goes directly to the furnace blower relay to run the blower and also goes to the sail switch.

2. After a delay of 15 seconds or so the blower relay clicks on and sends main power to the blower motor. If your meter shows the thermostat signal is making it to the blower relay and the relay clicks (listen carefully, the click isn't loud and doesn't happen for a while!) measure to see that the relay is really sending power to the motor. No power, bad relay or relay not grounded. Yes power, bad motor.

3. The blower motor starts moving air and within three or four seconds the moving air turns the sail switch on. The control signal goes on through the sail switch and on to the high temperature cut-out switch.

4. If the high temperature cut-out switch is OK and the firebox isn't VERY VERY hot, the control signal goes on through to the control board.You should be able to measure the control signal at the high temperature switch, both in and out.

5. On getting the control signal, the control board wakes up and twiddles it's thumbs for another 30 seconds or so to make sure any explosive gas is flushed out of the system and then passes the control signal on to to the gas valve and to the spark igniter section of the control board. If this is working you will hear a fairly loud "Click!" from the gas valve and a "tick, tick, tick..." from the electric spark igniter.

6. The gas valve clicks open and allows gas to go to the burner, where the spark lights it, making the familiar "Whump" of the gas lighting, followed by the rumble of the burner. If the gas doesn't light, then there wasn't any gas to light or the gas valve didn't really open or something is keeping the spark from lighting it. Here's where the control board earns its pay by  shutting the gas valve off and going into a fairly complicated sequence of purging, and trying to relight the burner. If you got this far it's a good time to evaluate your abilities and maybe call a pro to take over because it can get pretty hairy to fix from here on out.

Take your trusty meter and try to follow along with the above narrative and see if you can find where the expected sequence stops and you'll probably find the bad actor! If not, report back here with how far you got and what you found and maybe we can help!

Good luck!

 

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On 12/2/2020 at 1:58 AM, Harvey Babb said:

A real quick walk through of what is supposed to happen:

0. We're sitting here with a tank with LP in it, and 12 volts making it from the battery through the fuse to the furnace and the thermostat happily showing numbers that say it's healthy and ready to server.

1. Thermostat decides it's colder than what you told it you like and sends control signal asking for heat. The thermostat does this by sending 12 volts to the furnace to signal it to wake up and do its job. This signal voltage goes directly to the furnace blower relay to run the blower and also goes to the sail switch.

2. After a delay of 15 seconds or so the blower relay clicks on and sends main power to the blower motor. If your meter shows the thermostat signal is making it to the blower relay and the relay clicks (listen carefully, the click isn't loud and doesn't happen for a while!) measure to see that the relay is really sending power to the motor. No power, bad relay or relay not grounded. Yes power, bad motor.

3. The blower motor starts moving air and within three or four seconds the moving air turns the sail switch on. The control signal goes on through the sail switch and on to the high temperature cut-out switch.

4. If the high temperature cut-out switch is OK and the firebox isn't VERY VERY hot, the control signal goes on through to the control board.You should be able to measure the control signal at the high temperature switch, both in and out.

5. On getting the control signal, the control board wakes up and twiddles it's thumbs for another 30 seconds or so to make sure any explosive gas is flushed out of the system and then passes the control signal on to to the gas valve and to the spark igniter section of the control board. If this is working you will hear a fairly loud "Click!" from the gas valve and a "tick, tick, tick..." from the electric spark igniter.

6. The gas valve clicks open and allows gas to go to the burner, where the spark lights it, making the familiar "Whump" of the gas lighting, followed by the rumble of the burner. If the gas doesn't light, then there wasn't any gas to light or the gas valve didn't really open or something is keeping the spark from lighting it. Here's where the control board earns its pay by  shutting the gas valve off and going into a fairly complicated sequence of purging, and trying to relight the burner. If you got this far it's a good time to evaluate your abilities and maybe call a pro to take over because it can get pretty hairy to fix from here on out.

Take your trusty meter and try to follow along with the above narrative and see if you can find where the expected sequence stops and you'll probably find the bad actor! If not, report back here with how far you got and what you found and maybe we can help!

Good luck!

 

I went through all of the above steps and at the end it was the burner that had o hole burnt out of it due to 10 years of use.  I replaced the burner and all was well.  

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