Furnace works fine with heat but shuts off after few minutes

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  #41  
Old 11-19-14, 06:13 AM
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After removing one connector

Placed jumper between two switch terminal and got flashing error on control board - pressure switch open with induce on

Then


Placed jumper between WIRES and system ran without any issue
 
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  #42  
Old 11-19-14, 06:29 AM
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I suggest you restore pressure switch wires to original configuration. If the furnace ignites and operates for awhile use your finger to flick the pressure switch to see if the pressure switch opens. That would indicate weak contacts.
 
  #43  
Old 11-19-14, 07:11 AM
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Ok, will try when i get home later today. Beside what you think if it's not pressure switch then is it inducer?
 
  #44  
Old 11-19-14, 08:12 AM
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Beside what you think if it's not pressure switch then is it inducer?
Jumping out the pressure switch merely simulates a closed pressure switch. The closing of the pressure switch is meant to be accomplished by the inducer when the vent system is in proper working order. The only accurate way to prove if the pressure switch is defective is with the use of a magnehelic gauge or manometer.

To verify the operation of the pressure switch during a call for heat the magnehelic gauge or manometer is connected into the pressure switch tubing with tees so that you are reading the negative pressure developed by the inducer. This is what the pressure switch is sensing and closes by. Pressure switches labels have their close setting shown on the label. With the inducer running, the gauge or manometer will indicate the pressure sensed by the pressure switch. This pressure should be higher than the close setting indicated on the label. If the pressure is not above the switch setting, there is a problem with the furnace. If the gauge or manometer indicates higher pressure than the pressure switch close setting indicated on the label, yet the switch does not close, the pressure switch is defective.

Some of the causes of an open pressure switch during a call for heat are debris in the inducer blower housing, seized induced draft blower wheel, failed inducer motor, cracked heat exchanger, pressure switch stuck open, etc.

So without a gauge or manometer about all you could do is replace the pressure switch and see if it corrects the issue you are having.
 
  #45  
Old 11-19-14, 10:51 AM
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I searched few manometers and looks like there are different types, do you have any recommendation?
 
  #46  
Old 11-19-14, 02:23 PM
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You need one which will read down to 0.1" W.C. It must also be able to read negative pressure.
 
  #47  
Old 11-19-14, 04:02 PM
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So i did finger flicking on pressure switch while it was closed and heat ON... it did not open to stop the system.

So does that mean its not weak contact and may not be bad then.? May be its something inducer portion you mentioned.. huh.. next big phase now
 
  #48  
Old 11-19-14, 04:44 PM
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So i did finger flicking on pressure switch while it was closed and heat ON... it did not open to stop the system.
How long were you able to get the furnace to operate? It doesn't prove anything really. I always flick them and if they shut off that easily I replace them because the contacts are probably getting weak. The manometer tells the whole story whether or not the inducer is doing it's job and if the pressure switch is not doing it's job if the correct pressure is being supplied.

Did you perform the test to check voltage across the pressure switch to see if it will remain at 0V while the inducer is running?
 
  #49  
Old 11-21-14, 04:45 PM
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Update.. i came home y'day and temperature was down to 65 and furnace wasn't running.... so not sure what was going through.. but i gave hard flick to pressure switch and guess watch.. since then furnace is working 100% fine.

i think there must be something wrong with pressure switch.. i guess will order new one to replace.

its been about 24 hours and 20 degress outside.. and furnace is keeping it up..
 
  #50  
Old 11-21-14, 05:11 PM
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Yup, sounds like it's pressure switch time.
 
  #51  
Old 11-21-14, 05:41 PM
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Glad to you hear you were able to narrow down the culprit of your issue. Here is a link to a parts diagram and list (page 10 and 11) for your furnace:

http://www.nordyne.com/literature/7087000.pdf

It is important to match the specs of the pressure switch.
 

Last edited by firedawgsatx; 11-21-14 at 06:05 PM. Reason: Added link
  #52  
Old 11-21-14, 06:04 PM
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Thanks everyone for your help.. especially @firedawgsatx
 
  #53  
Old 11-22-14, 12:25 PM
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Ummmm. This thread seems to illustrate ther weaknesses of GUESSING AND SUPPOSING as diagnostic methods.


<<Update.. i came home y'day and temperature was down to 65 and furnace wasn't running.... so not sure what was going through.. but i gave hard flick to pressure switch and guess watch.. since then furnace is working 100% fine.


We are well into the 21st century, and beating the sucker to death with a hammer still seems to be the diagnostic method of choice.

As suggested, using a manometer to check out a pressure switch is the right way to diagnose difficult pressure switch problems. Often you can work around that because a bad pressure switch is VERY RARELY the problem. Pressure switches usually operate reliably, and so ASSUMING that they are not the problem when they stay open is a reasonable supposition.

But if you want to KNOW if you have a opressure switch problem, you need a manometer and the skill to use it. It would be rare for a DIYer to have a manometer and that skill, and all too often it's rare among repairmen, too.
 
  #54  
Old 11-24-14, 04:29 AM
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I understand your skepticism however i put in exactly what happened... May be THIS PART was made by 20th century boy

I just got new pressure switch and looking to buy manometer, let me know if any expert recommendation.
 
  #55  
Old 11-24-14, 04:19 PM
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I use & have had good luck with the 2 port version of this manometer. No idea as to cost. EM151 | UEi Test Measurement Tools
 
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