OP
Problem solved: It was a broken C wire, and bad information from Nest. The Nest will operate without the C terminal connected, but it shouldn't be allowed to and I never should have left it that way for the long term. Without a C wire Nest was only able to charge when Heat, Cooling, or Fan were running. It siphoned a little power off the top for charging and wifi. Apparently that didn't cause a problem for Heat or Fan but on Cool, something was sensitive enough to get interrupted.
The blue (C) wire was not providing a ground at the thermostat. I verified this by killing power, moving the blue to the same terminal as red, then testing continuity at the thermostat end. No go. I took a closer look at the thermostat wire bundle and realized there were 5 or so unused wires. Pink now connects to the C terminal at the board, and the C plug at the thermostat base. I get 27V from R-to-C and the system has been running smoothly for close to an hour with the Nest back in place.
I got a spare board out of he deal and *could* have fixed it for 0$ if I was good enough. How much would I have spent to pay a tech to scratch his head over it? I dunno.
@BlackGun you were a huge help and I want to buy you lunch and a beer next chance I get. Thanks man!
The blue (C) wire was not providing a ground at the thermostat. I verified this by killing power, moving the blue to the same terminal as red, then testing continuity at the thermostat end. No go. I took a closer look at the thermostat wire bundle and realized there were 5 or so unused wires. Pink now connects to the C terminal at the board, and the C plug at the thermostat base. I get 27V from R-to-C and the system has been running smoothly for close to an hour with the Nest back in place.
I got a spare board out of he deal and *could* have fixed it for 0$ if I was good enough. How much would I have spent to pay a tech to scratch his head over it? I dunno.
@BlackGun you were a huge help and I want to buy you lunch and a beer next chance I get. Thanks man!
