Ruud furnace exhaust fan

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  #1  
Old 03-18-18, 06:23 AM
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Ruud furnace exhaust fan

Hi, 17yo Ruud model UGPJ 07EAUER nat gas upflow furnace with LUX TX9600a thermostat. Lately, I have noticed the exhaust blower cycle seems different. Checked it this AM when furnace lit at end of the nightly setback period. The exhaust blower is coming on, but the distribution blower is starting at the same time. The exhaust blower used to come on a minute or 2 before the burners would light and I believe go off when the burners lit? Now, it seems everything is coming on at once at start of a heat cycle, burners, exhaust fan and distribution fan. End of cycle the gas valve turns off and the distribution fan runs a coupe minutes more. This seems normal. But the exhaust vent fan runs also all the way through the heating stage, isn't it supposed to shut off early in the heat stage? The exhaust pipe is very hot to the touch, seems like I'm losing heat that way? Thank you for any input.
 
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Old 03-18-18, 06:45 AM
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The inducer runs through the entire heating cycle, that’s how your venting the products of combustion outside. An 80% furnace flue pipe will get hot to the touch.
Not sure on the blower starting at the same time. The blower delay switch may be getting weak. Is the unit getting a simultaneous call for heating and indoor blower at the same time?
 
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Old 03-18-18, 06:51 AM
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Yes, the furnace blower starts at same time the burners light. No delay.
 
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Old 03-18-18, 12:15 PM
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More info: Now the system seems to be running correctly. The inducer comes on a few seconds to a minute before the furnace blower starts. So the issue is maybe intermittent? Is the blower delay a piece that can be easily replaced? Or is it a part of the control board?
 
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Old 03-18-18, 12:49 PM
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UGPJ ...... are you sure there is a J there ?

Be sure you accurately watch what is happening.

1) call for heat
2) draft inducer starts
3) pressure switch proves and ignition cycle begins.
3) within 30 seconds ignition starts.... either hot surface or intermittent pilot.
4) within 30-45 seconds the burner lights.
5) if timed..... the main blower comes on in 30-60 seconds.
........If not timed... actual heat switch starts the blower.
6) call for heat ends. Burner shuts off.... draft inducer shuts off. Main blower runs for approx 90-120 seconds.
 
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Old 03-18-18, 02:31 PM
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Yes, just verified it is a "J" model according to manufacturer label inside unit.

How do I know when the system "calls for heat?"

(the inducer is a Jakel model 117847-00)
 
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Old 03-18-18, 02:42 PM
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When the thermostat circuit closes between R and W
 
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Old 03-18-18, 03:22 PM
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Usually when the draft inducer is running.... there is a heat call.
 
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Old 03-20-18, 07:53 AM
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The plot thickens..........just arrived home, house feels a little chilly. Thermostat shows temp to be 68, heat set at 70. Furnace not running, not a peep from it. Pulled panel door off unit and made the door switch and green light comes on on the circuit board. Furnace still does not start. Switched thermostat on/off a couple time.......nothing.
 
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Old 03-20-18, 12:17 PM
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At the control board.... jumper W to R. You'll have to hold the door safety switch in for the test.
 
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Old 03-20-18, 09:10 PM
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The system seems to be operating correctly now. I changed the thermostat batteries and replaced the filter while I had the panels off(it was at 245 hrs of 250 hr filter cycle). Cooler weather predicted here for rest of the week so I'll pay attention and see if it keeps cycling correctly. Thank you for your assistance.
 
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Old 03-25-18, 07:46 AM
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System continues to cycle properly. Thanks for all the input.
 
 

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