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I have a lennox elite series heater that is giving a

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pressure switch error code. the...
I have a lennox elite series heater that is giving a pressure switch error code. the draft inducer motor is not coming on and I don't know why? Figured that is why I am getting a pressure switch error
Submitted: 11 months ago.Category: HVAC
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Answered in 8 minutes by:
11/22/2016
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 11 months ago
Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 953
Experience: I have been an HVAC/R mechanic/technician for 30+ years.
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Hi I'm Brian and I'm here to help! The inducer motor starting is the first step in the heating cycle, all else depends on that blower starting and the resulting proof of run from the pressure switch. The only things before this in the cycle are the shorting of terminals R to W of the furnace control board by the thermostat. If the thermostat isn't working or there is not incoming power or 24 volt power, these things could cause that. The first thing to do is confirm you have power to the furnace, then 24 volt power within the furnace then a call for heat from the thermostat. If any other mode on your thermostat turns on your furnace's blower fan then you confirmed the first two. If you then take a small jumper wire and short R to W on the furnace control board, you are simulating a thermostat call for heat and this can tell you whether the thermostat is working or not. If you still get no inducer fan when you've confirmed incoming power and 24 volt power by trying another mode and you've further shorted R to W on the furnace control board, then it's likely either the inducer fan motor itself or the relay on the furnace control board that operates the inducer fan has failed.

Let me know if you have questions about this.

Thanks,

Brian

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Customer reply replied 11 months ago
When I jump r and w I can heAR a clicking sound
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 11 months ago

If you feel the end of the inducer motor after you hear the click with R to W jumped, if the motor is getting warm or hot but not running, that indicates a failed inducer motor. If the motor stays cold then you may have a bad relay on the furnace control board that will not pass power to the inducer motor.

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Customer reply replied 11 months ago
Yeah the motor stays cold. Which one is the relay and can this be replaced
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 11 months ago

I'm not sure which relay on the board is for the inducer motor. We don't replace relays on the boards as they are soldered in. We replace the boards. If you're really handy at stuff like this, inducers are available online for most furnaces. If you'd like and you give me the full model number of the furnace, I can source one for you.

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HVAC Technician: Brian HVAC Guy, HVAC Technician replied 11 months ago

Boards are available too. It would be best to use a volt meter to doubly confirm that your inducer motor is not getting power when it should before condemning either the board or the inducer motor. I can source a board for you as well.

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Customer reply replied 11 months ago
How do I check to see which is bad. I have my volt meter
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 11 months ago

If I can get the furnace model number, I can give specific instructions but as a general instruction, if your inducer is not a variable speed motor and if you have 120 volt power to the inducer on the two wires going to it but it won't run then you have a bad motor.

If you hear the click and have 120 volt ac power between the power line wire (not neutral wire) going to the inducer and the Line wire (L1) coming into the furnace control board, that tells you the relay is not passing power through the board to the inducer when it should be. This means the board has failed. Again that's a 120 volt back feed between Line power on the board and the switched line terminal that goes to the inducer. When the relay is energized and calling for the inducer, there should be 0 volts there not 120. There should only be 120 volts there when the inducer is NOT being called to run.

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Brian HVAC Guy
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