Inducer vacuum issue with 80 % gas furnace


  #1  
Old 01-25-19, 10:28 AM
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Inducer vacuum issue with 80 % gas furnace

I'm having intermittent vacuum issue. When the inducer starts I get about 1.25 iwc vacuum at the vacuum port. The unit goes through its cycle but by the time it is near the end, the vacuum has slowly
decreased to about .8 iwc of vacuum, which is the set point for the switch. Most of the time it completes the cycle but sometimes the switch will drop out.
Here is a list of things that I have done, with little to no improvement:
* Cleaned the entire flue pipe and cap. * Cleaned through inducer vent. First I vacuumed it out then I put shop vac hose on blower and blew through heat exchanger.
* Cleaned burners and burner area.
* Cleaned inducer vacuum port with a small wire bottle brush.
* Checked power and amp draw on inducer motor. (120 volt ac, .6 amps on 1 amp rated motor)
I'm ready to pull my hair out ! Any ideas would be appreciated. Thanks.
Jim
 
  #2  
Old 01-25-19, 11:26 AM
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Sounds like maybe the pressure switch is doing its job and may be a crack or hole in heat exchanger? Especially since this is happening as it runs longer. I have had this happen and found cracks during heater replacement.
 
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Old 01-25-19, 12:46 PM
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Did you also make sure inducer blower wheel is intact and in good shape?
 
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Old 01-25-19, 01:15 PM
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That would suck! I will borrow an exaust gas analizer to check that out. Thanks.
 
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Old 01-25-19, 01:19 PM
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Yes. The inducer motor turns freely and the wheel is clean, in excellent condition and runs vibration free.
 
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Old 01-25-19, 07:14 PM
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Welcome to the forums.

* Cleaned inducer vacuum port with a small wire bottle brush.
Most vacuum connection ports on the inducer blower have a tiny pinhole at the bottom of the barb that needs to be cleaned. A small drill bit, a large sewing needle, etc can be used to clean it out.

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  #7  
Old 01-26-19, 03:37 PM
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Thanks Pete I will check that out. Mine makes it a little difficult because mine is about five inches long and curved into nearly a 90 degree arch from end to end. Thanks.
 
 

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