Replaced both thermistors. Unit cooled to proper temps, shut off, then 10 minutes later the compressor began its regular routine of trying to start (relay buzzing) stopping for a couple of minutes, and trying again, and so on. Here is a new and curious symptom: After the compressor tried and failed to start a few times I turned off the unit, unplugged the wiring harness to the relay, turned the unit back on with a volt meter on the harness to see if it was still getting 120v (all OK) turned the unit off, plugged the harness back in, turned the unit on, compressor started right up EVEN THOUGH HOT!? With the volt meter in place I had jiggled every wire in sight trying to see if I could get a voltage drop, nothing, a nice steady 120, so I don’t think that I inadvertently made a better connection when reattaching the harness. A lose connection is something I looked for right from the start, and wiggling the wiring harness to the relay, pressing in on it, etc.,, when the compressor was trying to start all had no effect.
I went the through a similar routine a second time when the compressor failed to start hot, omitting only the attaching of the voltmeter: turned the unit off, disconnected harness to relay, turned the unit on, turned it off again, attached harness, turned unit on: hot compressor started up. VERY strange to me, any help to you?