I’m installing a nest thermostat and trying to turn off power to the thermostat before doing so. I’m using a voltage tester and can see the wires coming in have power. I have two systems, one for upstairs and one for the basement. I’ve turned off the furnace breaker for both, and even pulled the large pull out head for the system, and the thermostat still has power. I don’t have any other breakers indicating anything for the HVAC system. I then started flipping off breakers for the surrounding area, and still has power. How/where in the world is this thing getting power from? Am I missing something else somewhere?
Can’t turn off power to thermostat
hvacthermostat
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Nest states their thermostats do not require a Common 24 volt leg of control power to be provided to the Nest, However there are some situations where the Nest will not stay charged after a bit thus requiring a Common leg of the 24 volt power sent to it, they allege the Common leg back feeds
to the thermostat by unused circuits and it does in many if not most cases however there are many complaining after a week or so of the Nest no longer operating or operating normally, this is due to no Common leg in most cases.
Yes, it is easy to control a swamp cooler with any thermostat. The problem is that in order to use a swamp cooler effectively, you need strategic openings (typically open windows) to let the air out. This is the part which is hard to automate. The best way to use a swamp cooler is to open windows in the rooms that need the cooling the most. You want as much windowspace opened as possible without any outdoor air coming back in through the windows. There are some automated devices I've seen (such as UP-DUX that vent into the attic but they cause additional resistance so they are much less effective.
Your drawing has a couple of problems...
- You need to use the Rc terminal
- The coil on your R8222B1062 needs to connect to the Y2 and the C (not the R)
- I don't think you want to connect to the C terminal on the nest because your heating system is already providing the C to power the thermostat.
- I think you're right about this one but I wouldn't rely on the thermostat powering Y1 and Y2 simultaneously when it called for high. I would rather to design it so that if the Y1 is not powered but the Y2 was, it would still run on high. This gives you a little more redundancy in case of a relay or wire failure.
Below is a drawing that would fix these problems but it is much more generic, the only specific part is that Packard contact delay because I am unfamiliar with a generic part name for that. If you fix 1 - 3, your design should work flawlessly. Again, the exhaust ventilation is your biggest problem.
I would put a nice 24v DPDT relay and a nice 24v 3PDT relay on the appropriate mounting sockets and mount them to a DIN rail. This will make it easy and clean. Put it all in a box with the transformer and the Packard and voila.
Best Answer
BRHANS is absolutely right. Use a multi-meter to check for actual "voltage". 24 volts A/C is the minimum voltage you should have. You said you have two systems. By chance do you have a zone control board for any other zones?? sometimes they have their own transformer and a separate control wiring. If you do NOT have a zone control board, get a multi-meter that can do LOW A/C voltage and verify the voltage. Check voltage at "R" to "C". with power ON you should have 24v A/C. If you still have voltage with the system off, you will have to check power at the HVAC equipment. I'm not sure the age of your furnace/ air handler, but some of the older equipment has a separate Transformer that runs the low voltage side only. This may have a separate power source as well. ( not very common) but I have seen this situation in the past. Hope this helps. and good luck to you.