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Old 12-17-2013, 07:40 PM   #1
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Air handler fan stays on


The system has three components:
Goodman air handler ARUF036-00A-1
Honeywell thermostat TH4110D1007
Rheem heat pump 10PJB36A01

Worked fine for years, but now the air handler fan runs continuously whenever the thermostat switch is at 'heat', regardless of temperature or heating. The fan is not stopped by disconnecting the green wire on the thermostat 'G' terminal (fan). The fan stops only when the switch is set to 'off', or the thermostat is completely disconnected.

One possibility is a stuck fan relay, but replacement & testing show the relay/time delay board are fine. With the thermostat fan switch 'off', jumpering 24vac to the fan terminal on the relay board causes the fan to start normally. The fan stops after some delay when removing the jumper, as I believe it should.

There is a 2nd 'heat' relay in the air handler. It seems to be working properly since it clicks, and the fan stops when the relay coil is not energized.

When I look at the way the system is wired, it does not correspond exactly to any of the reference diagrams I have found. It is possible that some unintentional wiring changes were made at the last service when the unit was moved, and it is only become obvious now that cold weather is here.

What I am left with is either the thermostat itself is bad or the wiring is incorrect. There should be some basic tests I can do to isolate the problem.

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Old 12-17-2013, 08:27 PM   #2
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Air handler fan stays on


Had a heat pump system in the middle of the night come on and stay on, turned out it was a bad wire from the air handler to the heat pump.

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Old 12-18-2013, 05:01 AM   #3
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Air handler fan stays on


If it only stops by turning the thermostat system switch to off. Its either the thermostat, or a wiring short.
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Old 12-18-2013, 04:34 PM   #4
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Air handler fan stays on


I have removed & tested all the air handler components, and they seem OK. The heat pump functions OK, and I don't think it could cause this issue. I checked the thermostat settings and they are set to suggested values for a heat pump system.

I walked thru some diagnosis with Honeywell(india), and they claim the thermostat is OK, but shortly afterwards I was able to determine that the thermostat 'B' terminal (changeover heat) is always energized when the thermostat switch is set to 'heat'. I don't know if this is normal or not, but it is the reason the fan runs all the time. The signal from the B terminal is wired directly to the air handler electric heat relay which also activates the fan. Disconnecting the B terminal opens the relay and stops the fan. I hope this proves the thermostat is at fault (or mis-configured), since I see no other explanation.


Troubleshooting this system has been complicated by the limited/incorrect documentation. These are fairly simple systems, yet finding correct and complete documentation is challenging, and seems to include several options and exceptions to the way the system may be wired, even depending on the brand of components. HVAC installers should be required to provide the install manuals for each sub-system and an overall system wiring diagram.
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Old 03-18-2014, 11:27 PM   #5
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Air handler fan stays on


After some months of not using the heating, the original installer was able to drop by and take a look. It turns out he had replaced the thermostat in the prior season, and the problem behavior (B terminal always on) was because the new one was simply the wrong model. The system needs a 2H1C thermostat and he had used a 1H1C model. Once the correct thermostat was used, it all works properly.
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Old 03-19-2014, 04:49 AM   #6
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Air handler fan stays on


Thanks for the update.

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