Is NEST 2nd gen compatible with Trane XC95M and XL16i? I have an XL900 (TCONT900AC43UAA) thermostat that controls my heat pump/furnace and want to replace it with NEST 2nd generation but not sure if it will work. I removed the faceplate of my XL900 thermostat and it only shows three wires. The wires or slots that the wires plugged in to are not labeled. Thanks in advance.