Help...Indoor Blower won't shut off on this unit

[atcherservice]

I am working on a 15 year old Carrier Gas Pack unit that the Indoor fan blower runs even when the unit is not calling for cooling or heat. I have replaced the Iindoor fan relay, and still the same results, I am wondering if the Time Delay relay needs to be changed out. Have never come accross this situation any feed back would help.

Thanks

Ken

Atcher Service

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[applianceman18007260692]

If you disconnect the thermostat does it still run all by its lonesome? How does the heat come on? Fan/limit? Maybe the limit is stuck?

[dkpd1581]

First check that there is not a high ohm short to ground in the blower motor that is causing it to find an alternate electrical path and making it run.

Second, if the unit has a Honeywell combination fan limit switch in the heater section and the unit is in a high ambient condition in some attic or closet, check to see if it has not changed state and energized the circuit

I had a church unit - only runs on Sunday - in a mechanical closet that the ambient air got hot enough for the bi-metal combination switch to spin and energize the fan circuit as if the heat exchanger had come on.  I adjusted the cut in temperature a bit higher - greater than the room temperature that could not be vented or conditioned - and this shut the fan circuit down.

Also, check to see if an open limit switch in the heat circuit is causing the fan to run.