I just moved into a new apartment with HVAC, and I'm looking to control the thermostat with a few Phidgets (I had already invested in that ecosystem, so I just needed a couple of relays).
Anyway, when I connect the R and G wires together with my relay, the system turns on both the fan and the compressor (the letter behind the green wire is indeed labelled G). I'm guessing this isn't normal; how would I go about troubleshooting this? I haven't had the chance to turn the Fan switch to "On" on the original thermostat to verify its operation.
Shorting the blue wire (labelled Y in the photo) and R turns on the compressor + fan as well, which is expected.