I have a Carrier Infinity system - full system (heating and air conditioning) newly installed a little over a year ago (southern Ontario, Canada).

I have programmed the system for continuous fan operation - the furnace fan should always be running at some modest speed. When new, it worked as expected - fan speed ramps up or down between continuous fan speed and heating or cooling speed (depending on season/mode).

During the current cooling season, I have recently noticed a different behavior. The furnace fan sometimes shuts off completely along with the A/C compressor, until the A/C cycles on again. This is intermittent because the fan sometimes does just ramp down to its "continuous" programmed speed as I expect it to.

Is the system intermittently shutting down because it detected a problem? If so, what might the problem be? Could it be icing up? Is this what the system is supposed to do if it detects what could be icing condition (evaporator temperature/pressure too low)? Is this a fault requiring a service call?

  • 1
    I would look at the control board for error lights when the system shuts down.
    – Ed Beal
    Sep 2, 2018 at 16:59
  • 2
    Some electric companies have a billing option allowing them to shut AC during peak usage. See baltimoresun.com/… . Did you sign up for that option? Sep 2, 2018 at 17:04
  • @DrMoishePippik I'm aware of that option, refuse to have anything to do with it. Vaguely recall my thermostat has the option somewhere, made a point of not allowing utility control, but can't seem to find the setting now to confirm it's still "disabled".
    – Anthony X
    Sep 2, 2018 at 17:13

1 Answer 1


What the Dr. Mentioned will be located outside by the air conditioner and not in the settings. Count the boxes at the air conditioner. One is the disconnect for the air conditioner. If there is another then that will probably be it. However I do wonder, does the furnace sense air flow? As in filter clogged. Best thing is refer to the manual for your model of furnace to see if it indicates error codes.

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