If I leave my fan switch on "on" instead of "auto" and the temperature in the house reaches the desired temperature will the fan stay on and continue to push cool air out even though the thermostat turns the compressor off.


Yes, that's what "on" means. It means the air handler will keep operating, even though nothing is heating or cooling the air.

Whether this is a good idea depends on how your system is setup and what is going on.

If you are getting thermal separation ceiling to floor or upstairs to downstairs or sunny to shady side, it can be helpful at evening things out.

One person on here a few weeks ago had a problem where one side of their house was much hotter. So they had their air conditioning re-"balanced". Now the side with the solar load got a lot more A/C; this also meant the other areas got a lot less. With so much less air conditioned (dry) air, condensation started to occur. "On" might have helped them with their problem.

  • Harper that's exactly my problem. With the change of the angle of the sun, one side is getting hotter than it use to and the ac is having to work harder. – Clifford Williams Sep 30 '19 at 21:50
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    Do you mean than it used to this morning, when it used to since a ducting problem developed, when it used to before I painted that side of the house a deep color/re-roofed to black... Any idea what changed? – Harper - Reinstate Monica Sep 30 '19 at 22:04
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    My neighbor removed a pecan tree. That exposed that side of the house to more sunlight in the afternoon. – Clifford Williams Sep 30 '19 at 22:34
  • I leave my fan on all year round. It evens out the too hot or too cold places, eliminates stuffy rooms, and helps prevent dampness in the basement. The filter needs to be replaced more often, but perhaps that's a good thing. The extra electricity is about a dollar a day in summer, and in winter it's almost free (the heat produced by the electricity reduces the need to burn gas). – Ray Butterworth Oct 1 '19 at 15:25
  • Thanks Ray and Harper. I kept my fan on all day, with the thermostat on. It worked. The overly hot area stayed cool all day and into the evening. – Clifford Williams Oct 2 '19 at 2:58

Yes. the fan will stay on until you switch it to a different setting. Even with the compressor "off" the fan will continue to run.

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