Trouble with AC Soft Starter

I installed a Microair 368 Soft Starter for my 4 ton AC a few months ago:

Prior to this, the AC compressor, the (natural gas) furnace, and the HVAC blower fan are all detected separately and fairly reliably by Sense. However, after the soft starter was installed, I started having issues. I expected it will take a while for Sense to re-learn the startup pattern, so I waited patiently. Since the soft starter has Bluetooth, I can connect to it and see its status, including the number of compressor starts. It went something like this:

  • After 263 compressor starts, Sense detected a device and thinks it’s HVAC. I renamed it “AC Soft Starter”.
  • However, subsequent detection of AC Soft Starter was poor. Out of every 10 starts, Sense may only detect 1 or 2 of them.
  • This continued until about 800 starts. At this point Sense decided that it should merge “AC Soft Starter” with “HVAC Blower Fan”, and called the merged device “HVAC Blower Fan”.
  • Never mind that this is going to cause problems come winter time when the furnace and the blower fan will both run, but not the AC compressor. The detection has gotten even worse after the merge. Now AC is almost never detected anymore.
  • I waited until there have been over 1000 compressor starts to give Sense time to learn. Now, 1045 starts later, I’m starting to think Sense will never figure it out.

Has anyone had a similar set up? Any resolutions?

Based on a prior suggestion that I try this device for problems Sense is having with my geothermal system pump, I researched it pretty carefully. What I seemed to find out is that this device modifies startup (couldn’t find anything about shutdown) power curves, eliminating the sharp spikes and providing a gentle/gradual startup.

That’s exactly the opposite of what Sense needs, it depends on sharp/short on/off transitions for proper detections, one reason it fails for so many modern devices (like my refrigerator and dryer) that gradually ramp up and down and use only the power that’s needed.

So, I decided to avoid the Microair 368 Soft Starter (and saved $350) and lots of additional Sense frustration.

It does lower the startup current spike, from LRA of 112A to around 40A or so, but can vary between 36-44A. That’s still a significant spike though compared to its normal operating current date, which is 10-11A. Perhaps the variability in the startup spike is throwing Sense off.