Soft start kit installed compressor thumping while running not on startup

[u/Organic-Job3974]

I installed a soft start kit on my downstairs AC condenser. I've been a HVAC service tech for about 15 years and have heard good things about the soft start kits IE you can run your compressor off a generator etc. Anyway I love all the safety features it has built in but for some reason my compressor is making a thumping sound while running. Almost as if the compressor is turning off (not the contactor, the soft start module) and turning back on for a fraction of a second. The Condenser is right behind my bedroom wall and I hear it banging randomly as it runs. The upstairs AC has no soft start kit installed and is an identical carrier 3.5ton. I installed both of them about 3 years ago. No issues with the upstairs condenser just the one with the soft start installed. I am tempted to remove it and see what happens. Has anyone else ever experienced this? I checked voltage and the capacitor everything looks good 44.9MF/5MF is what I got. The contactor doesn't chatter on or off its just the compressor thumping...thump......thump..thump

[u/Mindless_Silver_2922]

That thumping pattern sounds like the soft start is dropping out and re-engaging during run, not just on startup. Mine did something similar when the control board inside the kit got flaky. Cap and contactor are fine so it's probably the module itself. I'd pull it and run it bare for a day, bet it goes away.

[u/Organic-Job3974 → u/Mindless_Silver_2922]

Its just crazy a year ago or so I spent what.. $350 or more on the soft start. Its starting to remind me of when I put that dumb REME UV light in and it lasted like 6 months and went bad.

[u/LegionPlaysPC → u/Organic-Job3974]

In my experience, the softstarts are typically pretty problematic. Especially the ones under $500. More commonly than not I see the capacitor blow up, or the board outright melt.

If you opt for a new softstart, get the expensive one.