OK, a summary,

Goodman/janitrol heat pump has been working well for 4 yrs. A couple of days ago, the thermostat went blank, with no power to the condenser or evaporator (no I haven't checked voltage yet). I assumed (sorry:() that it was the transformer, so replaced that. No avail. Still no power to anything.

It's supposed to be cold tonight (32F, but hey, I'm in FL), but the house seems to be well insulated; last night it only dipped to 58 inside, but nonetheless, please help. Is "labman' still here?

If it went Blank, it may have Batteries, and need replaced.

Update: Replaced transformer is warm to the touch in ambient 40F temps. Any thoughts now? Would greatly appreciate any help. I replaced the blower relay last year w/ great success; hoping for similar success again. Thank you for any attempts.

PS Stratmando, did check the thermostat for batteries; chip only. Thank you, though.

White is some times heat, Green is sometimes fan, sometimes cooling is blue or yellow, I would probably remove thermostat, Jump the red to different wires to see effects. The best that can happen is you determined thermostat is bad, System is good. Worst that can happen and not likely(usually you have one side of the transformer and the control wires, not the other side of the secondary) is a blown fuse feeding the 240 to 24 volt Transformer.

If you have a open main limit(roll out limit, vent limit) It will kill 24v. With a 4 year old system it should be protected with a low voltage fuse 5amp or 3amp auto fuse on the furnace control board. The unit control board should be giving you a flashing light code to tell you what's wrong. Good luck.