The stat is set up for2 heat 2 cool, the system that it is set for
Check and see if the stat calls for Y2 when the setpoint is 4° below room temp, after 5 minutes of first stage run time. You would check that at the unit, using your meter. If no call, I would take the stat off its base, and look for continuity between the Y2 prong and the Rc prong. No continuity in the stat under the conditions above, and I'd say you need a new stat. I would also check the stat wire by jumping R to G, Y1, and Y2, and check on the roof for both stages getting a call. If not, you have a bad stat wire.
Also, double check that all wires are landed properly on the stat base, using the top row of terminal identities, next to the word "conventional," and ensure that the small stainless steel jumper between R and Rc is tight under both setscrews.
[Avatar photo from a Florida training accident. Everyone walked away.] 2 Tim 3:16-17
An explanation is all I wanted. If you what someone to explain the set up for the stat ask for that, if you want someone to walk you threw testing the system ask for that to. personally if you work for me I'd feel better if you came to me and asked me what was going on, at least then I would know you want to figure things out and learn more, I wouldn't have given it to another tech though I would have taking you over and showed you how to troubleshoot it . That would be a win win situation. And I believe you were given info to trouble shoot it you just didn't reply.
Iam sorry for not responding, the task got handed over to someone less busy then I when you gave me the troubleshooting info. My service assignments were backing up and I had to move on. Out of my 7 years of being in the field I have not had that much trouble with 1 unit. I wish I had time to learn what was really wrong with it, it is not that I did not want to learn for my benefit here, it is the amount of service stacking up on me and I cannot sit on one call for so long. Sorry again for the inconvenience.