Furnace draft inducer problem


  #1  
Old 01-23-17, 03:12 PM
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Furnace draft inducer problem

Inducer fan and motor were getting really noisy so I ordered a new unit. After I put it on, the inducer runs , the burner ignites but goes out almost immediately. It will not stay lit. I checked and the vacuum switch is being activated by the fan. Ruud furnace. Put old unit back on and everything works fine with it other than the noise.
 
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Old 01-23-17, 03:24 PM
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Do you get a trouble code? Do you have a volt meter?
 
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Old 01-23-17, 04:56 PM
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It ignites four times then goes into one hour lockout mode. One flash. I have voltmeter. Voltage activating valve does not stay on long enough to measure. Was wondering if igniting the burners caused the vacuum switch to drop?
 
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Old 01-23-17, 05:00 PM
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Welcome to the forums.

Put the meter probes across the pressure switch terminals. At rest you should measure 24vac.
When inducer gets up to speed you should measure 0v and it should stay that way.

If it changes to 24v then you probably have an inducer leak. Possibly a gasket or sealing issue.
 
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Old 01-24-17, 10:31 AM
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Voltage drops like you said but when burner ignites there is voltage fluctuation and it stops the burner. I tried high temp sealant but did not help. There are no flaws in casting. Old unit still works perfectly. The new unit evidently isn't creating as much vacuum.
 
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Old 01-24-17, 11:36 AM
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Should probably check draft using a manometer and compare it to the pressure switch rating. Also check the venting for obstructions and make sure it was installed per the installation directions. Having to replace an inducer would also make me want to check the venting.
 
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Old 01-24-17, 12:11 PM
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I have checked the venting. Still works with old inducer installed. Will check switch rating. Something has to be different on new unit since old one works.
 
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Old 01-24-17, 12:53 PM
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Did you purchase an OEM assembly from the manufacturer of the furnace?
 
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Old 01-24-17, 02:16 PM
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I think I found the problem. Pressure switch was replaced 10+ years ago when it was sticking shut. Only one available in town was not original but it worked. Just looked at original switch and it was rated -.3 wc and the replacement was-.59wc. The new inducer has a 1/4" smaller diameter fan than the original so probably doesn't create quite enough vacuum for the heavier switch. Ordering a new switch today.
 
 

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