About 1-3 times per summer the same fuse blows in my AC service disconnect. Always the one on the left. The fuses are 30A and on the panel there are two 30A breakers. The fuse blows typically on a very hot day when the AC runs for quite a while. My guess is that there's just a bit more resistance on that side due to age ( or loose wire or evil spirits?) and that causes the fuse to fail. The breakers never trip.

Given that upstream there are 30A breakers the disconnect fuses don't seem particularly necessary (also the panel is ~5 feet from the disconnect). Is there any reason I shouldn't replace the disconnect with a non-fused model?

Does it even make sense that the disconnect itself could be the culprit, or should I be hunting other issues?

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Update: I replaced the capacitor with an OEM version (first replacement was not OEM), and the fuses stopped popping, the best explanation is that something was causing more resistance on one side of the disconnect which resulted in blown fuse when the unit was at high load (ran hot, decreased fuse life). The OEM capacitor had a CPT terminal and I don't think either of the previous capacitors did, so perhaps that made a difference too, unsure about that. Since then the whole unit has been replaced, and new disconnect. The OEM capacitor did get me an extra trouble free year.

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    Can you post a photo of the nameplate label on your air conditioner compressor? Commented Jul 23, 2019 at 11:42
  • @ThreePhaseEel Might have one from when I changed a capacitor a couple years ago will have to dig around a bit this afternoon. If not will get down there this weekend and can take a picture, but was hoping to address the issue while there.
    – Hart CO
    Commented Jul 23, 2019 at 14:05
  • I am confused. The lower wires look like normal #10 A/C wire but the feeder to this panel is much larger (not a bad thing, just odd). What is the circuit breaker rated at? Also what are the fuses rated at? Commented Jul 23, 2019 at 17:04
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    I’d like to see the panel with the cover off.
    – Kris
    Commented Jul 23, 2019 at 21:54
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    Will plan on getting more info this weekend, lift the panel's skirt for a few photos and get details on the condenser, check connections and report back. Thanks all!
    – Hart CO
    Commented Jul 23, 2019 at 22:12

1 Answer 1


The feed to the panel looks like #6 al and aluminum wire can loosen over time and with load. I'd check the connections in the panel. You can change the fusible disconnect to a non fusible one. Make sure it is rated for aluminum cable. You would need either a 30 or 60 amp depending on what you find when you get the name plate info. You've got breakers for the compressor and the air handling unit so make sure you know which ones are which, though the breakers for the air handler would be higher amperage if there's a strip heater in it.

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    I ended up not pursuing switching it out because the compressor was nearing end of life and an OEM capacitor seemed to fix the fuse issue for the rest of the unit's life. The unit has since been replaced.
    – Hart CO
    Commented Jul 12, 2022 at 15:12
  • @HartCO Thanks. It's nice to get updates on the questions we try to answer.
    – JACK
    Commented Jul 12, 2022 at 16:38

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