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I noticed my home gas furnace was turning on, I could hear it running, but it seemed the fan was not blowing the heat out of the heat duct vents...there was almost no air pressure. SO I went downstairs to the furnace, and looked at the red blinking light on my American Standard Freedom 80 furnace, and it showed 4 blinking flashes then a pause, so I looked on the error chart on the front panel, and it said "Open high limit device." I figured I would need to go and find my manual that came with the unit, to see where the "high limit" was located? Anyways, while I was there at the furnace, I figured I would jiggle the 2 electrical connections that connect to the fan housing. I just tried to get the metal on metal connection of the electrical connectors to seat slightly differently. I put the front panel back on, and the system fired up, and this time I could hear the fan running and blowing the hot air. I went upstairs, and yes, the heat vents had blowing hot air. Anyways, in the days before this I had been smelling an odd "electrical burning" smell, like a smell I had smelled before when I had a motor burn out, in some other unrelated tool. I'm just guessing that this smell is related to the new problem with the furnace? The filter was replaced one month ago.

Well, I was wondering if you could suggest some helpful hints and knowledge? I sure would appreciate being able to learn.

What does the HIGH LIMIT device do? Does "open high limit device" error code mean that the device is stuck open?

What do you think the "burning" smell is coming from? Which part would be affected in such a way as to cause this?

Thank you.

  • If the blower is not running, the furnace will surely overheat. Get the blower running, and you shouldn't have a problem. – Tester101 Dec 24 '16 at 15:49
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High limits and you

A "high limit" switch protects the furnace against overheating and damage -- it's located in the output duct, or plenum, of the furnace and turns the furnace off if things get too hot up there. The usual cause of a high limit trip is inadequate airflow -- in your case, because an apparently faulty connection was causing the fan to not run.

If you continue to get the "electrical burning" smell after fixing the connections -- that's a sign the fan motor on your furnace is on the way out the door. Generally, you'll need to have an HVAC service tech come in and swap it for a replacement. (If you can access the other side of the connection, you can also use a voltmeter to measure the voltage drop across it -- anything more than a volt is cause for serious concern.)

  • Not to be nitpicky, but the high limit is there to protect the equipment, not to prevent fire. Although, I guess it does also prevent fire. If the furnace gets hot enough to ignight nearby materials, I wouldn't recommend trying to use that furnace ever again (as it's probably a molten puddle at that point). – Tester101 Dec 24 '16 at 15:58
  • Thanks very much for you smart answers to my questions and my need for help...You answered everything I needed to know about my furnace problem, thankyou for taking the time! – user64183 Dec 28 '16 at 0:37
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I had the same thing. I checked both limit switches with a meter and the primary limit switch was open, but closed once it cooled off. It would heat up, light for a few minutes but the blower never turned on. This caused it to overheat so the induction blower turned on and stayed on to cool it off. This ind blower would not turn off until I unplugged it. It was the capacitor that went bad —$5-$25 depending on whether you buy Chinese or American. An hvac guy I know said to buy American because it will last longer. The capacitor is attached to the blower housing. Watch videos on how to change it.

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