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I have a Rheem RH1T6024STANJA hvac system, and after any heat cycle runs, the thermostat clicks off but the fan continues blowing for 3 minutes. Now I am fully aware that it is normal for systems to blow for about a minute to get residual heat out, but this is altogether too long. After about 30 seconds it's just blowing freezing air back into the house and by the time those 3 minutes are up the heat has to turn right back on, effectively running 24/7.

How do I reduce that after-cycle fan time? I've been told there aren't any DIP switches to adjust this on the unit itself, so would a new thermostat change anything? I was looking at a Honeywell RTH6580WF but now am unsure if that's the answer.

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  • Usually a thermostat just turns on/off certain controls on the furnace board. Might be a heat sensor or timer on the furnace that can be adjusted/changed.
    – crip659
    Commented Jan 24, 2023 at 14:58
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    Funny, the exact opposite problem of this question
    – FreeMan
    Commented Jan 24, 2023 at 16:11
  • The fan might be kept on by the thermostat's G wire, or by a high temp sensor in the heat exchanger or by a timer, or by a malfunction of any of those things or of the fan actuator switch. With the manual/schematic and a meter you can confirm or eliminate each of these things. If you set it up and rehearse it you might be able to confirm/eliminate all of them in a single 3-minute cycle.
    – jay613
    Commented Jan 24, 2023 at 18:03
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    But wait ... why is it blowing "freezing air back into" the house? Usually the fan circulates air through the house. It shouldn't be "freezing" although it may feel cool simply because it's flowing. It shouldn't be bringing air "into" the house. Perhaps you didn't mean that literally, you just meant that the unheated air from the registers feels colder than you would like? Two minutes after the fan has been circulating air doing its job, the air throughout the house should be fairly consistent in temperature.
    – jay613
    Commented Jan 24, 2023 at 18:06
  • @jay613 yeah I guess that's what I meant. But either way it's the only thing that accounts for running almost nonstop when it's not even that cold outside (50s fahrenheit)
    – mjr
    Commented Jan 24, 2023 at 19:51

4 Answers 4

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According to the manual it should be 30 seconds. Multiple references, including:

An off-delay is built into the control of the motor that keeps the motor energized for 30 seconds after 24 volts is removed from all speed tap terminals.

It should be 30 seconds no matter what, though the source of the 30 seconds varies depending on model. Based on the model #, you have an H1T, so it is part of the motor rather than the blower control board.

There is an exception when you are in electric heat (a.k.a., emergency heat, when the heat pump can't do the job):

There is a blower off-delay programmed into the blower control when a call for electric heating ends. The delay is 45 seconds for the White-Rodgers control and 30 seconds for the UTEC control. This off-delay is added to the 30 second off delay programmed into the motor for a total off-delay of 75 or 60 seconds. This allows time for the contacts in the bi-metallic disc type heating sequencer to open which de-energizes the heater elements.

but even that should not get it to 3 minutes.

So check with Rheem. They may refer you to a dealer. If the unit is under warranty this should be covered. If the unit is not under warranty then hopefully you can get some information about an adjustment somewhere instead of having to pay for a service call for someone to adjust it. My hunch is that nothing is truly broken as the more typical broken modes would be:

  • No fan at all (been there...)
  • Fan stops immediately (no 30 second delay)
  • Fan never stops
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  • ok I'll have to see what rheem says
    – mjr
    Commented Jan 24, 2023 at 19:52
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Could it be that your thermostat is calling for fan-only mode for a period of time? You could remove all doubt by taking a good photo of the current wiring, then disconnecting anything that's on the G terminal on the furnace controls.

If this blower behavior still occurs with nothing connected to the G terminal then I don't see any way that a new thermostat could correct the issue.

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According to the manual:Manual

The delay time off is programed in the fan control board.

fan

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A new thermostat won't correct that. There's a timing relay in the fan circuit that might be able to be adjusted by a screw on the top. You'll have to locate it on the wiring diagram of your unit and then on the circuit board or on the motor. Have you called Rheem's customer service and asked them?

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