Draft Inducer Motor turns on and off randomly (no heat called for)

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  #1  
Old 12-17-12, 08:27 PM
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Draft Inducer Motor turns on and off randomly (no heat called for)

Hi all,

I have been trying to troubleshoot this problem for about 2 weeks now with no luck. Here is my situation:

I have a 4 floor house with 2 furnaces (one on the first floor another on the 4th floor) + water heater all connected to the same chimney.

On both of my furnaces (which are identical Armstrong Ultra V Tech 80), model number #G1N80AU050D12A-1. I get the draft inducer motor randomly turning on and off when the thermostat is not calling for heat. Sometimes it will be for a few seconds and sometime it will run for about 15 to 20 seconds and shut off.

Here are the things I have done/unsuccessfully tried (and spent money on)

1) I tried completely disconnecting the thermostat, left the Red, Green, Yellow, White wires dangling to rule out this was a thermostat issue (the inducer motor came on randomly even during this test)
2) Installed a new thermostat for the lower furnace (heck maybe you need a pull up or down on the wires i thought) the inducer motor still randomly turns on and off.
3) Replaced the pressure switches on both of the units (didn't help at all but the replacement units look nice)
4) Replaced the control board on the lower furnace (no change still the inducer motor comes on and off randomly)
5) Turned the water heater on (by turning the temperature dial) to see if this resulted in the inducer motor to come on on the furnace doesn't seem to be related.
6) Adjusted the humidifier control doesn't seem to effect the inducer motor behavior.
7) New flame sensors on both of the units (doubt it was necessary that was a HVAC company suggestion)

Additional clue 1: i observed sometimes on the lower furnace; is the green LED will blink "only sometimes" 4 times (for this furnace this means "Open Limit Switch or Limit Switch Ciruit" ) while the inducer motor is running and no heat is asked for then it will go back to its good old heart beating mode (bright blink followed by a dim blink) without doing anything.

Additional clue 2: if i open a door on the bottom floor this does seem to effect/trigger the symptom of inducer motor coming on (not all the time though). This leads me to believe that i may have a pressure change in the house or draft from chimney type of an issue but have no clue on how to test this theory or remedy the situation.

I am running out of ideas so any help will be much appreciated. I did have a HVAC company show up but they haven't been able to diagnose the problem yet.

Other then the issue I described above the furnaces seem to be running properly and heat the house when necessary.

I have searched quite a bit on the internet and i do see a few people with similar issues but just never seems to be answered.
 

Last edited by efe476; 12-17-12 at 08:57 PM.
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  #2  
Old 12-17-12, 11:22 PM
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Cheap electronics thermostats which leak current when off may cause that problem, but you ruled that out.

Sounds like there could be a power quality issue. I don't recommend replacing more parts.
 
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Old 12-18-12, 08:41 AM
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thanks for the reply, how can i check for a power quality issue ? I don't see any lights flickering in the house.
 
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Old 12-18-12, 08:53 AM
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Makes absolutely no sense

I can't see draft having any bearing on the problem.
Flame sensor would not cause this.
The pressure switches are completely unused until there is a call for heat.
 
  #5  
Old 12-18-12, 03:52 PM
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^Ditto

--------------------------------
Start by making sure that the voltage at the furnace is stable (with a multi-meter) when the problem occurs.
 
  #6  
Old 01-02-13, 09:32 PM
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Wanted to provide an update on this issue in case anyone else encounters a similar problem. I finally found a HVAC company (priority heating & air conditioning) in Chicago that was willing to go the extra mile. Tom, was extremely helpful and after numerous attempts, got a hold of someone over at Armstrong to discuss the symptoms. Overall the diagnosis seems to agree with all your suggestions that there is something with electronics on this unit/model (combination of the smart valve which actually controls the inducer fan, the controller board and possibly some fluctuations in my household voltage "even though when i monitored it with a meter i am getting 118 ~ 119.5 V" that is causing this behavior). Long story short the only workaround (i am rather pissed that i didn't think of this myself) was to put in an extra relay (also recommended by Armstrong, this is such a hack and there should be recall on these units rather then technical support making a suggestion to install extra hardware) to monitor the "call for heat" and only allow the inducer fan to turn in this case. The relay was put in by splicing the inducer fan live wire on the high voltage side and connecting the call for heat (24 V wire) from the thermostat on the low voltage side.

Anyway the workaround does take care of the problem of the inducer fan getting turned on and off randomly. But overall my take away is to stay away from any Armstrong furnaces (or anything labeled from the same manufacturing line) and going with a unit that can handle real life conditions properly (for ex: fluctuations in voltage) in the future.

Armstrong if you end up reading this thread please do us all a favor and actually publish some documentation acknowledging the problem and a possible workaround rather then punishing people out there to suffer with your faulty units and wonder why their furnace(s) keep turning on and off.
 
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Old 01-02-13, 09:54 PM
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Well......I guess that's one way to take care of the problem.
 
  #8  
Old 01-03-13, 12:05 PM
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You don't often see this kind of creativity in the HVAC trade!


Actually, you do ---- from time to time. Sometimes it's needed to make the SOB work.
 
  #9  
Old 04-01-13, 09:50 AM
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Additional issues

My furnace was exhibiting the identical symptoms and I performed the same steps to isolate the issue. In my case I also noticed that the rubber grommet that surrounds the gas pipe to the burner was burned and the part furthest from the burner was burned through. This area of the fire box never gets warm and there are no signs of charing on the label inside the furnace access door. Replaced the gas valve which did not correct the problem. After running overnight the furnace appears to be working normally with no random restarts. Voltages all appear to be normal but if this starts again I will install the relay as indicated.
 
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