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Discussion Starter · #1 ·
I was testing furnace before winter...rudd acheiver 90 plus model# ugra-07emaeb. Fan running as soon as i power on furnace with wall switch..have to cut power to to furnace to stop the fan from running.
--Thermostat calls for heat properly..nothing at furnace
-- filter is new...fan is clean
-- green light flashes 3 times..2sec pause..flashes 3 times..etc..
*** inside panel says limit switch is open
-- main limit switch ohms properly with beep from multimeter
-- 2 other switches near burner area ohm properly also
-- put a jumper wire between both red wires from main limit switch..no change?

Any idea where to look next?
Could the main limit be bad even though there is continuity?

Pictures posted



Thanks in advance
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I was testing furnace before winter...rudd acheiver 90 plus model# ugra-07emaeb. Fan running as soon as i power on furnace with wall switch..have to cut power to to furnace to stop the fan from running.
--Thermostat calls for heat properly..nothing at furnace
-- filter is new...fan is clean
-- green light flashes 3 times..2sec pause..flashes 3 times..etc..
*** inside panel says limit switch is open
-- main limit switch ohms properly with beep from multimeter
-- 2 other switches near burner area ohm properly also
-- put a jumper wire between both red wires from main limit switch..no change?

Any idea where to look next?
Could the main limit be bad even though there is continuity?

Pictures posted



Thanks in advance
View attachment 710616 View attachment 710616 View attachment 710618
--Thermostat calls for heat properly..nothing at furnace

Can you explain ?

Does it mean Thermostat is not turning the furnace on/off ?
 

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Discussion Starter · #5 ·
--Thermostat calls for heat properly..nothing at furnace

Can you explain ?

Does it mean Thermostat is not turning the furnace on/off ?
I set the thermostat for heat..2 degrees higher than room temp..fan set for auto...turned on power for furnace.( wall switch was off for summer) heat only furnace..fan immediately started to run..no heat...thermostat was showing heat mode...could only stop fans running by powering off furnace with wall switch...thermostat would not turn off fans even when I reset temp to cooler than room temp.
 

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I set the thermostat for heat..2 degrees higher than room temp..fan set for auto...turned on power for furnace.( wall switch was off for summer) heat only furnace..fan immediately started to run..no heat...thermostat was showing heat mode...could only stop fans running by powering off furnace with wall switch...thermostat would not turn off fans even when I reset temp to cooler than room temp.
Do you have a Pilot light ? is it ON ?
 

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Ohm out and entire limit circuit from the board connection (disconnect individual wires or molex - whichever is there), could be a bad connection or even an aux limit in the blower compartment open.

Use the schematic to guide you.

...and "ignore run a gate".
 

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Discussion Starter · #11 ·
Ohm out and entire limit circuit from the board connection (disconnect individual wires or molex - whichever is there), could be a bad connection or even an aux limit in the blower compartment open.

Use the schematic to guide you.

...and "ignore run a gate".
There looks to be 3 limit switches.. they ohmed out as working ..everything worked well last winter...powered down in spring till now
 

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There looks to be 3 limit switches.. they ohmed out as working ..everything worked well last winter...powered down in spring till now
You need to ohm out the entire limit circuit from the connection to the board with it disconnected from the board, since the individual switches are closed.

This is to see if limit circuit is actually open, the connection to the board is the issue or the board itself is defective - closed circuit, good connection but board still reporting open limit.
 

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Discussion Starter · #13 ·
You need to ohm out the entire limit circuit from the connection to the board with it disconnected from the board, since the individual switches are closed.

This is to see if limit circuit is actually open, the connection to the board is the issue or the board itself is defective - closed circuit, good connection but board still reporting open limit.
I followed wires from switches to a connector on board...removed connector..wires from switches ohmed properly...beep
 

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Connection to the board or board itself.


With a call for heat and door switch depressed, you can try pushing on the connector and moving the wires around to see if the code goes away and blower turns off.
 

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Discussion Starter · #15 ·
Connection to the board or board itself.


With a call for heat and door switch depressed, you can try pushing on the connector and moving the wires around to see if the code goes away and blower turns off.
Unplugged and Ohmed 2 connectors..1 inline and 1 at the board...both seem fine..beeped
I'll try your other suggestion later but connectors seem solid...
I'm still looking for the pilot light 😉

Was hoping I could just swap out the main limit and fire up..guess nothing is that simple
 

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Unplugged and Ohmed 2 connectors..1 inline and 1 at the board...both seem fine..beeped
I'll try your other suggestion later but connectors seem solid...
I'm still looking for the pilot light

Was hoping I could just swap out the main limit and fire up..guess nothing is that simple
If you jumper it at the board and it still gives the error, you'll need a new board. (if it starts up, don't run it like that.)

Post a picture of the board/wiring and the wiring diagram.

PS. Ignore runagate
 

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Was the furnace working properly during the cooling season?
Unless you shorted the board somehow it is unlikely the board went bad just switching from cool to heat.
And the usual question.....how old is the furnace?
 
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