E89 error: Y/Y2, no Y1 wire. Nest App said connect Y2 -> Y1 port, but cooling does not work :(

[austindavid]

My original thermostat has a Y2 wire, but no Y1: see attached.

Nest app said to plug into the Y1 terminal, and the "technical info" etc finds all the wires, reports cooling + heat + stg2 heat as expected, and heat + fan work fine.  But cooling doesn't work, it just seems to blow fan-air or possibly warm air.

Running the troubleshooting and in the cooling area it goes to E89, which doesn't have docs 😞

To be sure, I put the old thermostat back up and cooling works fine.  Nest doesn't report any other errors; it seems to be getting power fine and otherwise behaves.

[CoolingWizard]

@austindavid , the Y1 and Y2 are the Compressor Stage 1 and Stage 2 cooling.  The E89 error is reported when there is a wire attached to Y2 and no wire is detected in Y1.  You cannot have Stage 2 without a Stage 1 wire.  Please post a picture of your Nest Thermostat backplate so I can see the wires that are attached.  Thank you. 

AC Cooling Wizard

[austindavid · Accepted solution]

i figured it out; the system is a heat pump and the wire was actually an O.  I traced back to the source and hooked it up correctly, all is well.