Announcement

Collapse
No announcement yet.

Home improvements - 24 VAC power HVAC thermostats, doorbell

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Home improvements - 24 VAC power HVAC thermostats, doorbell

    This may sound stupid as I've been owning my own home for 42 years now and I've never actually had to deal with the low voltage power 24 VAC

    I know that I use 24 VAC (nominal it actually measures 27.6 at my thermostat) for my two Thermostats (upstairs and downstairs) and the doorbell.

    I think there is one transformer I see screwed to a stud up in my attic with an AC switch next to it.

    Is this likely that one transformer provides 24VAC to all my thermostats and doorbell system?
    Or does each AC/Heating unit have its own 24 VAC source?

    I'm finally installing a Nest Thermostat and was trying to figure out the easiest way to turn off the power to the thermostat. I don't think just turning off the AC system breakers will kill the 24 V, if its its not normally provided by the AC, is it?

    Last edited by LCHIEN; 01-10-2020, 06:36 AM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

  • #2
    I would be surprised if the doorbell 24VAC is the same as the A/C unit. Usually the A/C unit has the low voltage as an integral part of the unit. Other forums have discussions about a missing wire causing grief. Be sure the required feed contains all the spec'd wires.

    Comment


    • #3
      To kill power to the thermostat you usually need to turn off power to the furnace / air conditional control system, assuming they are integrated. I've never seen a doorbell attached to the same wiring as a thermostat.
      Chr's
      __________
      An ethical man knows the right thing to do.
      A moral man does it.

      Comment


      • #4
        OK, THanks. I'll turn off the breaker to the A/C unit and see if the 24 V goes away.
        Loring in Katy, TX USA
        If your only tool is a hammer, you tend to treat all problems as if they were nails.
        BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

        Comment


        • #5
          That’s going to bug the crap out of me now until I find out where my doorbell transformer is hidden..... and the 24v power comes from for my thermostat.

          Comment


          • #6
            You guys are wrong so far. I turned off the 50 Amp AC breaker and the thermostat still has power.
            Loring in Katy, TX USA
            If your only tool is a hammer, you tend to treat all problems as if they were nails.
            BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

            Comment


            • #7
              Hmmm. Local codes probably vary from location to location. Around here, the door bell transformer is usually wired off of another circuit. Ours has always been the basement light circuit as the wiring is close and the load is very small. Our water meter sender is wired off of a basement wall outlet circuit. The thermostat around here is to be wired off of contacts within the HVAC unit and thus is powered by the HVAC unit. If you want to spend the money, perhaps one of the circuit identifiers available from the big box stores would help you find the breaker powering your thermostat. I suppose being in TX, you don't have a basement, so I'm probably no help.
              Last edited by Jim Frye; 01-10-2020, 06:44 PM.
              Jim Frye
              The Nut in the Cellar.

              Comment


              • #8
                The reason I didn't want to poke around is the rats nest of wiring in between my two HVAC units.
                There's a giant rats nest of telephone/networking cables.

                THere's two transformers mounted to the stud, one a plug in type in a plastic case and the other a metal frame type
                And a box with two wall switches and a box next to it with a duplex plug in which the plug-in transformer goes.

                The metal transformer terminals are exposed and has three terminals of which two are connected. 17 VAC between the two used ones and 34 volts on the other. Doorbell? Some low voltage jacketed cable runs off somwehere... doorbell I'm thinking
                The plug in Transformer has a white and white strip zipcord going into the big rats nest I can't figure where it goes. I'm thinking its the alarm system power.
                The two switches look like they have Romex going off to the HVAC units. This looks promising. Turned them off and a faint hum in the HVAC went off. And I checked the thermostat and its got no power.
                So those two switches control whatever 120 V stuff is in the HVAC... it s old tech so I suspect just the transformer.

                Anyway, My thermostats each have a switch of their own, in the attic.But the transformers are in the HVAC unit.
                Last edited by LCHIEN; 01-11-2020, 03:36 AM.
                Loring in Katy, TX USA
                If your only tool is a hammer, you tend to treat all problems as if they were nails.
                BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                Comment


                • #9
                  Originally posted by LCHIEN View Post
                  The reason I didn't want to poke around is the rats next (nest) of wiring in between my two HVAC units.
                  There's a giant rats nest of telephone/networking cables.
                  LOL ! I never heard it called that, but it sure is descriptive. I have several of those in our attic also, and our house is 85+ years old! Of course that is not the original wiring either.
                  Hank Lee

                  Experience is what you get when you don't get what you wanted!

                  Comment


                  • #10
                    Nest Thermostat E is installed and appears to be working.
                    Now to connect it to google home and alexa
                    Last edited by LCHIEN; 01-11-2020, 03:52 AM.
                    Loring in Katy, TX USA
                    If your only tool is a hammer, you tend to treat all problems as if they were nails.
                    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                    Comment


                    • #11
                      this is the rats nest i was talking about. Frightens me to touch it and I am an electrical engineer, I did mess with the phone wiring once... back when we had modems to call the internet I had a second phone line and converted the upstairs to use the second line as the main pair. Anybody remember dial up modems?

                      Click image for larger version  Name:	20200110_180742_resized.jpg Views:	0 Size:	85.0 KB ID:	838290
                      Attached Files
                      Last edited by LCHIEN; 01-11-2020, 03:55 AM.
                      Loring in Katy, TX USA
                      If your only tool is a hammer, you tend to treat all problems as if they were nails.
                      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                      Comment


                      • #12
                        Connected to Google Home, wifi appears to be working but A/C is below par. Nest is saying it will take 1.5 hours to come down four degrees (info I never had before) and sure enough air coming out the registers is barely 69F. I should have checked AC performance before I changed the thermostat (good advice) but the thermostat appears to be working right and the compressor is running and cooling. I had the compressor replaced a few months ago, maybe I have leak. Oh well it is 73 degrees outside and humid today but I don't think the A/C repair guy is too busy. Or maybe he is, front just blew in but not too cold.
                        Last edited by LCHIEN; 01-11-2020, 03:51 AM.
                        Loring in Katy, TX USA
                        If your only tool is a hammer, you tend to treat all problems as if they were nails.
                        BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                        Comment


                        • #13
                          Last news. The thermostat I took out was from 1991. An old Honeywell

                          Click image for larger version  Name:	old honeywell mercury thermostat.JPG Views:	0 Size:	40.9 KB ID:	838293
                          Apparently there's a strong push to recycle these properly as they have a capsule of mercury attached to a bimetal strip used to make and break the contacts when the bulb is tilted. It is actually a mechanical marvel. Got some clever mechanisms in it to have adjustable hysteresis and stuff.
                          So I gotta take it in somewhere.
                          I have an upstairs A/C I suppose I should convert it too.

                          I never converted from the original because my wife was stay at home and there was never a schedule where we were consistently out that could be programmed.
                          Loring in Katy, TX USA
                          If your only tool is a hammer, you tend to treat all problems as if they were nails.
                          BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                          Comment


                          • #14
                            Not only do I remember dial up modems, I still have the old 56 kb/s one we used when we first got a computer that could attach to the internet. Why? it's in a box along with other computer memorabilia I have saved to confound my kids when I'm gone. There's some 8", 5", and 3 1/2" diskettes. 80 and 96 column punch cards, Magnetic data cards, and the old IBM Portable Terminal (aka "the Brick") that customer support folks carried. I also have two THINK signs, one of which is in braille.
                            Jim Frye
                            The Nut in the Cellar.

                            Comment


                            • #15
                              I've got a couple of 8" disks, a 20MB full-size drive, Laserdisc, a functioning original Newton, some mag core memory (64 BYTES!), and others. I keep meaning to build a shadow box display for all of it.

                              Comment

                              Working...
                              X