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 Repairing and Servicing Lennox Products
 Repairing / Servicing Lennox Gas Furnaces
 My Lennox G50UH is not automatic any more
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wendydog

6 Posts

Posted - 02/14/2010 :  4:14:46 PM  Show Profile  Reply with Quote
Help: I have a LENNOX M/N G50UH 36B 090 01, S/N5800M 44140. When you turn on furnace the status light on the main board shows normal--slow flash/slow flash.when it calls for heat lights fast flash/fast flash,nothing happens except the light on main board tells error off/slow flash. If I pinch rubber hose or pull lead from pressure switch and replace. Furnace fires normal.When room reaches set temperature the furnace shuts off, but the combustion air inducer never shuts off. light on main board shows error off/slow flash. When thermostat calls for heat I have to pinch rubber hose or pull lead from pressure switch and furnace will fire. The main control board & pressure switch (49L9101 replacement switch )about a year ago by a service tech. This problem has happen off and on ever since. he said he did not know what the problem was and wood not come back. please help?

slctech

2085 Posts

Posted - 02/14/2010 :  8:00:00 PM  Show Profile  Reply with Quote
The control board is designed to monitor the pressure switch for two types of faults
1) If switch is closed prior to a call for HEAT
2) If switch opens during a call for HEAT

It appears to be that after a call for HEAT that the inducer motor is not being deactivated by the board (faulty relay). Thus, it continues to run keeping the pressure switch closed, upon the next call for HEAT the board doesn't realize that the inducer motor is stuck on, it just realizes that the pressure switch is closed and will fault out.

Replace the board

As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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wendydog

6 Posts

Posted - 02/18/2010 :  11:29:12 AM  Show Profile  Reply with Quote
I received New Pressure switch from Cozy Parts yesterday 2/15 installed it furnace same as before as I posted on 2/14/10. today 2/18/10 to start furnace same as before at 5:30 am, when it shot down and called for heat the furnace started normal by it self. after blower comes on air inducer shuts off. It run for about 6 hrs with know problems. Then the same problem as before.
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Cozy.Support

5773 Posts

Posted - 02/18/2010 :  4:48:16 PM  Show Profile  Reply with Quote
If the induced draft blower is not shutting off, replacing the induced draft pressure switch is not going to solve the lockout issue. If the induced draft blower stays on between cycles, the furnace will not come back on at the beginning of the next heat cycle. The circuit board looks to see if the switch is open (fan off) and then looks to see if the switch is closed (fan on). Also, if you have any other issues that can cause low induced draft fan pressure, you can get a pressure switch code. Most pressure switch diagnostic codes do not result in a bad pressure switch. Most of the time, there is other issues causing the circuit board to set the induced draft pressure switch code.

If the call for heat is satisfied, and the inducer continues to run, you would be suspicious of the circuit board, as stated by SLCtech in the beginning of this thread. The key to a good diagnosis is knowing for sure that the call for heat from the thermostat has ended and that the inducer is continuing to run after the call for heat has ended.



CozyParts.com, Inc. is an Independent Lennox Dealer providing a national parts distribution resource for Lennox parts since 2002. The Cozy.Support team does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx
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slctech

2085 Posts

Posted - 02/18/2010 :  8:22:52 PM  Show Profile  Reply with Quote
Replace the board as I stated in my previous post. Pressure switch has nothing to do with your symptoms, your symptoms actually prove the pressure switch is doing it's job.




As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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wendydog

6 Posts

Posted - 02/19/2010 :  08:51:46 AM  Show Profile  Reply with Quote
quote:
Originally posted by slctech

Replace the board as I stated in my previous post. Pressure switch has nothing to do with your symptoms, your symptoms actually prove the pressure switch is doing it's job.




As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!

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wendydog

6 Posts

Posted - 02/19/2010 :  09:19:24 AM  Show Profile  Reply with Quote
Thanks: Slctech: I have one question, after staring furnace same way as I had before, for some reason the furnace working normal , air inducer shuts down when thermostat reaches set temp. Air inducer runs until heat is satisfied.Is this normal. Thank you.wendydog
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slctech

2085 Posts

Posted - 02/19/2010 :  09:24:49 AM  Show Profile  Reply with Quote
Sticking relays on a board have their good days and bad days. Just a bump to the board could free up the relay and you will run fine for a few days to a few years. There is no rhyme or reason to the relay failures.

As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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