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My HVAC is a heat pump system, the air handler inside is a Goodman aspf183016ea. The whole system/house is about 3 years old, and is all electric. I recently moved into the home and noticed that the air handler blower would continue to run even when the set temp was reached, whether heating or cooling; the condenser unit outside would shut off correctly, but the fan would continue to blow. This even occurs when the thermostat is set to off (fan is set to auto). The fan would occasionally shut off, but it was very rare. I had a technician take a look and he said the issue was probably a bad relay switch. He replaced it, but I noticed the issue was still present and called him back. He said he wasn’t sure why it would still be doing this, but replaced it again with a “heavy duty” one and just ensured me that even if the fan blows, it wouldn’t draw much power.

Now, the fan does shut off when the set temp is reached, but it keeps turning on and off in 10-15 minute increments; I’ve timed it, and it’s not exact every time. I’ve also noticed when the fan does come on (when the set temp has been reached and shouldn’t be on), I hear an audible noise from the blower unit, like a switch activating, before the fan turns on. I’ve since replaced the thermostat (formerly a Honeywell FocusPro 6000) with a Nest Learning Thermostat E. All the connections were made accurately, and the heating/cooling/fan controls work properly, however the fan still switches itself on and off in the same intermittent manner. I know the Nest thermostat has a setting to run the fan every hour for a set amount of time but I haven’t activated this.

Is the problem still with the relay switch, and should I have a technician take a look again? What else could the problem be?

  • If you turn thermostat completely off or unplug it from the wall does the fan still periodically turn on and off? With todays modern high-tech thermostats, you really have to rule that out as a cause even if it means replacing with a super-cheap manual thermostat for a week or two. – JPhi1618 Nov 3 '17 at 18:57
  • Yes the only way the fan turns off is if I turn off power/flip the breaker. – bblmaster Nov 3 '17 at 21:22
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    Your relay is doing exactly what it is being told to do - turn on. The circuit that controls that relay is where there is an issue (if the relay is energizing that is). Inside your Air handler cover there is a wiring diagram - Take a good picture of that diagram and post it here and I can look at it and know what controls the relay and also how that blower is connected. – Ken Nov 4 '17 at 8:09
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I have a picture of a similar units wiring diagram, your unit might have connection for an optional outdoor thermostat - W2 on thermostat via outdoor thermostat to brown wire on air handler (if the outdoor thermostat is optional on your system - the diagram on the panel will tell you) and it will also describe how to install with out the outdoor thermostat by connecting the brown and W2 white leads together. Again the panel has a wiring diagram - take a good picture of it and post it everyone can be much more helpful with that.

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