four flash on night and day furnace

Old 11-12-14, 07:31 PM
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four flash on night and day furnace

I have a 4 flash issue with my day and night N8MSN0701412A1 I replaced the 165 degree limit switch because that's what the guy I had in today said was wrong. After I put in the new one got the same thing and the switch ohm'ed open any thoughts or ideas on what could be causing the over temp? Some background: new filter, all ducts and registers open, unit installed Oct 2013 but there was no Tennant in the unit last winter to confirm if this has been a continuing issue.
Old 11-12-14, 08:14 PM
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Welcome to the forum!! Did the person who diagnosed that it was the limit switch actually test to see if it was opening while the furnace was in operation? You have some of the common causes covered. I would suggest to make sure the vent pipe is not blocked/restricted, return air ducts are not blocked by furniture or other object, make sure the air filters are not too restrictive and make sure the blower speed is set properly. Other factors that can cause the issue is inadequate supply ducts and not enough return air. Here is a link to the installation and parts manuasl that may provide some additional info to you:

Checking the list for 4-flashes there are multiple possibilities for a cause. It is shown in figure 44 on page 38 in the installation manual.

Last edited by firedawgsatx; 11-12-14 at 08:53 PM. Reason: Added links to manuals

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