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My 27 year old Carrier Super Saver furnace fan blower stays running even when the thermostat is off. After some troubleshooting, found out that fusible link connected to what looks like a limit switch P/N 4283A was blown. Replaced the fusible link, furnace ran fine for 15 minutes, then no heat, only cold air coming out of vents. Fan/blower keeps running. Whats causing the fusible link to blow. Filter underneath th

  • Looks like this post was cut off. – Tester101 Nov 30 '15 at 22:21
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Your high limit switch may be bad, and need to be replaced.

Your furnace may be overheating, and the limit is not reacting. So the fusible link is doing just what it's supposed to.

There are a few things that can cause the furnace to overheat, a dirty filter being the number one cause.

  • Thanks for the quick response. I ordered high limit switch, P/N HH12ZA161A thru North America HVAC. Will update as soon as the part arrived and have it installed. Filter underneath the blower compartment, washable type, is clean coz I washed it during the summer. But i noticed that there is a tear on the corner of the filter about 3"x4" that look like a rat chewed on it. – Efren Dec 1 '15 at 23:58
  • High limit switch came in. Replace washable filter with new one, remove blower and cleaned it with compressed air. Installed new limit switch and fusible link. Again, the furnace ran fine for approximately 15 min, then it cut off. One thing I observed is the flame is not all blue, but with some orange on it. – Efren Dec 11 '15 at 0:15
  • Has anything changed with the system, or did this just start happening out of the blue? – Tester101 Dec 11 '15 at 0:52
  • Do you have a blocked/clogged/restricted exhaust vent? Are you watching the furnace cycle? If so, do you notice any flame coming out of the combustion area (rollout)? Is there any sign of flame outside of the combustion chamber (scorching, charring, melted wires, etc.)? – Tester101 Dec 11 '15 at 1:05
  • Orange flame could be dust that you have stirred up but I would not run this or any furnace without a carbon monoxide detector especially one that has non blue flame. – B. Kaneer Jan 27 '16 at 3:45
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Its not the flue pipe. That is a seperate circuit with a different fault code. If you have air conditioning, check to see if the evaporator coil is dirty. Your furnace goes off on limit due to lack of airflow. Therolloutswitch is a manual reset so if you have reset it the furnace would not uave ever come back on.

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