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hvacdave84
hvacdave84, HVAC Technician
Category: HVAC
Satisfied Customers: 67
Experience:  ARI and EPA certified
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I have a Tempstar Furnace. The plenum fan stays on and the

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I have a Tempstar Furnace. The plenum fan stays on and the exhaust fan is not activating. Thus no ignition cycle. I checked the sensor loop. All switches (overtemp and dome) seem OK. Dome open/closed makes no effect on problem

hvacdave84 :

Hello, I'm Dave. I'd be glad to help

Customer:

Well, What can you offer on the problem?

Customer:

I ran out of time before I had to go to work.


 

Customer:

I cannot rate until interaction with hvacdave84 actually happens


 

Customer:

Dave


 

Customer:

Can you hear me dave?


 

Customer:

Stepped out? He never made it in!


 

hvacdave84 :

most times, if the blower runs without anything else happening, it is either due to an open High limit switch, rollout switch, or some other fault involving excess heat in the furnace


 

Customer:

Hi Dave, Furnace is stone cold no heat.


 

hvacdave84 :

Right. If a manual reset limit switch gets tripped, (such as a rollout switch or an auxilliary limit) it will remain open until physically reset by someone. the control board will sense the open switch, and run the blower as a safety precaution. no matter what happens, it will ONLY run the blower, until the limit is reset.


 

Customer:

How does one reset this switch


 

hvacdave84 :

check near the burners, for small circular switches with little "buttons" in the middle. try pressing each one. if you feel a click, the switch was open and you have just reset it.

hvacdave84 :

if that doesn't turn up anything, check the rest of the area where the inducer (exhaust) motor and piping is for the same type switches. If nothing there, check in the blower area. In front, on the sides, and behind the blower housing (you would see wires going back there, that aren't attached to the actual motor)

hvacdave84 :

if possible, see if you can snap a picture of the wiring schematic on the furnace door, and sens it to me. that would help me help you troubleshoot it.

Customer:

I'll give that a try and be right back. The circuit for the overtemp sensors is in concert with the Dome temp sensor. when i unplugged and checked for opens on them, the only thing that caused change was when I diconnected the o


 

Customer:

circuit loop from the main controller.


 

hvacdave84 :

also, have you tried shutting off power to the furnace, and turning it back on?


 


Sometimes if the automatic reset limit (priXXXXX XXXXXmit) has opened too many times repeatedly, it will cause the control board to lock out, shutting off and restoring power to it can reset it.

hvacdave84 :

Do you mean that you had continuity while the loop was connected to the board, but showed open when it was disconnected?

Customer:

 


 

Customer:

That would be a fair assumption...I found a sensor near the burner opening. At first it was visible but through bypassing it I was able to obtain ignition cycle and burner ignition. After I removed it from the chassis there was a red plastic unit between the terminals which ended up being the reset (although it was not typical in appearance) It clicked like you described. When I reconnected the sensor, it functioned fine.


 

Customer:

Your answer was spot on! Thank


you

Chat seemed to be giving us problems, so I switched us to Q&A. Try the things I've listed, and get back to me.
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Customer: replied 4 years ago.

Added info.....I went to a local p;ace to order a new roll out sensor, and the techs there were inquisitive as to the cause of the repeated sensor trips. They sent me home to do more tests which revealed a low chamber suction. I tore everything down after getting a look at an expanded view on a Sears site. Condenser unit was the problem....big hole in the endcap (which is plastic)22 years old, it just could not take the pull. Thanks.

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