Saw this device on the freon line at the compressors on a one year old house today. Took the pictures intending to ask about them here. They are wired to the thermostat control wires. Have never seen this before.
At the end of the inspection while talking with the homeowner, they came up. He had mentioned at the start of the inspection that he thought the compressors might be noisy. I told him at the end that I thought they were not noisy at all, that he must be getting used to having them going again now that winter is over.
Anyway he proceeded to mention that the things the Builder added to make them quieter must be working. When I asked him to expand on that, he said that he had originally complained about the down stairs unit being extremely noisy at start up. That the builder had installed the devices to fix it. That they would somehow modulate the freon flow or power flow to happen gradually and reduce the noise and (the builder said) they would actually make the units more efficient.
So, what are these? What do they do? Do they do what the client was told from the efficiency end? He said they had indeed improved the compressor start up noise.