Old model Carrier 396F Furnace fan won't turn off

Old 11-09-20, 02:28 PM
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Old model Carrier 396F Furnace fan won't turn off

Hey all,

My parents have an older Carrier furnace (model 396F - I don't know when this was installed but it's pretty ancient. Full model is 396F AW000100). My mom was saying that with the t-stat FAN turned to "Auto" the fan never turns off after the heat comes on (there is no cooling/AC/condenser). They have to kill power to the entire furnace to get the fan to turn off. I just asked if switching the FAN to "OFF" turns the fan off but I'm thinking they tried that and it doesn't turn off. My mom told me they have to either unplug the furnace or hit the breaker switch to turn it off.

At this point, I'm more curious to know what you guys think it is: likely the control board?

Since I'm far and even though I'll be there for a week during Thanksgiving (despite my mom asking for my advice/opinion) it sounds like my brother who lives there is pushing for them just to have his HVAC guy check it out and make recommendations on a replacement furnace. Not sure if it's true or not, but they claim to have never changed the furnace since they've moved into this house (which was in the 1970s), so I think it's time for a new furnace regardless - seems like it should help on the electric bills.
Old 11-09-20, 03:16 PM
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The FAN ON/AUTO switch will not cause the fan to stay on unless in FAN ON mode.
That is an old furnace. It would not be a bad idea to have it checked out and cleaned by a service tech. With age.... the heat exchangers get rusted and can rust thru causing high amounts on CO in the heated air.

I see that furnace uses an ignition control module that lights the pilot with a spark igniter.
I can't find accurate tech info so I don't know if that uses a timer controlled blower or a fan/limit switch.

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