limit switch

[tlcreager]

I have a miller furnace model G6RC080C-16 its 12 years old. It has been experiencing a problem with the limit switch (part #626446) for almost a year. Sometimes it will blow the fuse on the main computer board and other times it will just cut out the flame and try and relight after a few seconds, but it doesn't run a complete cycle. We have replaced the main board once and the limit switch several times. This last time we ordered a nordyne part from this web site thinking that maybe the furnace is sensitive to after market brands. Each time we bypass the switch the furance will run the complete cycle and be fine, but as you know this is not safe. The switch is for 140 degrees, but when the furnace is running the limit will open at 112 degrees. Any ideas? We have had 2 different furnace repair companies out to look at it and it will run ok for a while and then back to the same old thing. Any suggestions or solutions would be greatly appriecated.
Thank you
Terri

[Robert]

Hi,

The limit should not be opening until the heat chamber reaches the limit temp of 140*.


However, if you have replaced it several times, they cannot all be bad limit switches.


Because the limits are a safety component, my suggestion would be to find a good reputable hvac tech who will not leave until problem is found.


Not something I can do from here, but can say that with fuse blowing sometimes, it is probably an intermittant short in heat circuit somewhere.


Thanks,
Robert