Fan Limit - Blower goes too long

Old 12-08-09, 12:49 PM
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Fan Limit - Blower goes too long

I have a Trane XL80 gas furnace from approx 1992. House is 1 level, 2300 sq ft. It's cold out but noticed this issue prior to latest cold spell. Heat cycle starts fine runs for a while then when heating stops fan continues until air coming out the vents feels cold, approx 70f according to temp probe I have. At that time setback thermostat sends another call for heat and we start over. Fan essentially runs non-stop and house goes from warm to cold and back.

Looking at fan limit switch, Honeywell L4064T 2333 that's now obsolete. Fan off is 90, Fan on 130 and high limit is 150. If I try setting fan off to 100 it seems to slide past that and will continue to run until well below 70. Won't stop until I manually move the fan off again.

Does does limit switch wear out and need to be replaced? How can I tell? What should the settings be? Seems like 150 is low and is 130 too low as well? Looks like the L4064W replaces this unit.
Old 12-08-09, 01:06 PM
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Usually I'd set the fan off temperature to about 100.

Since this switch is failing, I'd experiment with the fan off temperature and see if you can find a setting where it will shut off properly, regardless of the nominal setting.

You should be able to get a replacement switch --- I probably have one in parts left over from my furnace repair business.
Old 12-08-09, 02:24 PM
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No expert..but remember..something that hasn't been moved in years..may need to be cycled a few times. Back and forth..back and forth a few times may make a difference...and make sure you hold the "dial" as you move the set points..twisting the dial around will mess up the guts...

Had kinda the opposite issue would shut off..then turn back on about 60 sec later..adjusted it down about 5-10 degrees..then all good.

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