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My AC unit is working just fine and shuts down at/below set temperature. However, the AC fan keeps running all the time even in auto mode. The only way I can shut down the AC fan is to power-down my HVAC system, wait for some time and then power it back again. What could be the problem?

Furnace Model: 58MVB100-F-10120 AC Model: 24ANA748A0030020 or 24ANA748A00300

I would appreciate any recommendations on what diagnostics I should perform in order to identify root-cause and fix it.

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  • Has this always been the case or just recently?
    – JACK
    Sep 20, 2019 at 1:09
  • It happened recently. Background: My HVAC unit was running fine until about 2 months ago. About 2 weeks ago my AC stopped running. I checked the unit and found out that both the start and run capacitors had both blown off. So, I purchased brand new start & run capacitors (both identical in their specifications to the original ones) and replaced them in my AC unit. Today I noticed that while the AC is running, the AC fan/blower were not shutting down (even in auto mode).
    – user97485
    Sep 20, 2019 at 2:22
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    Check the blower relay as it could be sticking. After that, check the thermostat fan/auto circuit.
    – JACK
    Sep 20, 2019 at 11:31
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    @jack that should be an answer. I find many times when a system has failed caps the high current caused because the motor could not start can weld the contacts or cause them to start sticking. On big systems I burnish the contacts with diamond burnishing tools but small ones I usually replace.+
    – Ed Beal
    Sep 20, 2019 at 13:40

1 Answer 1

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Check the relay for the blower in the air handler. It could be sticking due to pitted contacts from over currents from the motor not starting when the caps failed. Also, check the thermostat fan on/auto circuit. Good luck.

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  • I've been closely observing my AC unit for the past 5 days; it now seems to be functioning perfectly fine and shuts of the fan/blower from time to time when in auto mode. Thanks for your suggestions/help. If fan/blower shut-off problem resurfaces, I'll check the relay and possibly replace it.
    – user97485
    Sep 26, 2019 at 2:12

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