Furnace shutting off on overtemp

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GooGumper

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H, I have a 25 yr old Amana GUC70 gas furnace. It's worked well until this year, when some dummy, me, left out the air filter. The furnace started shutting off on the high-temp cutout.

I looked at the blowers and heat-exchangers and they ALL had a thick coating of pet hair and dust! I cleaned off the big blower, the first heat exchanger, and the AC evaporator. They are all now nice and clean and air should be able to blow through them just fine.

However the furnace still runs up right against the 200-degree high-temp shutoff mark. I can live with this but it looks less than optimum.

Is there anything else I can clean up to get more air flow and lower temps?

Thanks,

George
 
check the supply and return ducts, clean the secondary heat exchanger.
check blower speed wiring, you may have to switch some wires around so that the blower runs at high speed or med-high speed. Have a second shot at the evaporator coils as they may still be plugged up even the outer surface appears to be clean. Use a coil cleaning foam that will push the dirt out to the surface. Hose it off good or use compressed air or CO2, just be careful not to distort the coil fins.
I don't believe that this is a high efficiency furnace but, I had one the other day where the condensate line was plugged causing the limit to trip.
Also, some maintenance on the inducer motor may be in order to, along with the exhaust ducts. If the exhaust ducts are partially blocked, then the inducer won't be moving as much air and can cause heat build up.
 
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