I bypassed my AC thermostat with an ESP86 and a relay to control it with HA. By using tmp sensors in each room i have pseudo-smart thermostats (using the HA component). Great!
The other day I screwed my HA installation and lost control over the AC. I was not home and my wife was not happy (hot afternoon without AC). I learned the hard way that I need a backup plan.
The question is: is there any way to wire the relay with the old thermostat so the thermostat can override whatever the state is from the relay. That way, if there is an issue there is always a manual solution for a software problem.
I have found few topics talking about always keeping the manual option handy, but I honestly don´t know how to wire it. It may be a lack of the right terminology (is this called serial-relay connection?) to google the topic, so more than happy if you can just point me out to the right search.
thanks a lot! New to the forum here, but over a year playing with HA coming from doing it all on my own on a rpi.
You can have “mini automations” in the ESP (assuming you are using ESPHome?). So If you add a switch to the ESP, the firmware would recognize if you switch it and, well, switch on the AC.
This is completly independent from HA or even a wireless connection.
That´s a great idea, tanks. Just to be sure I understood correctly.
Using ESPHome (I use it) I could upload a firmware that considers HA input and/or the switch (the switch priority should be higher than the HA input). Even if HA is down or internet is down, for as long as the ESP is not dead I could control it with the physical switch. This option is also great because i think i could maintain the correct status even if someone switches on from the physical switch.
If so, Instead of a switch, do you think I could read directly the output from the thermostat? I need to check the voltage to not fry my ESP but in my mind it should work. To pass the Wife Acceptance Test she wants to be able to switch on and off from the old-fashioned wall thermostat.
To be even more secure, is there any wiring option that does not depend on the ESP? (I´m terrible at wiring, I always need to follow diagrams)
Connect your relay in parallel with the old thermostat. That way if the relay fails off, the old thermostat can always be used to control the system.
Of course it doesn’t help if your relay fails on, but usually that’s not going to happen and is a less troublesome scenario.
Another choice is a good old mechanical multi-pole switch. Connect common contacts to all the thermostat wires from the furnace, then one set of contacts to the old thermostat, one set to your relay(s). Then if something fails, switch can be set to “manual” to switch back in the old thermostat.
Using ESPHome (I use it) I could upload a firmware that considers HA input and/or the switch (the switch priority should be higher than the HA input). Even if HA is down or internet is down, for as long as the ESP is not dead I could control it with the physical switch. This option is also great because i think i could maintain the correct status even if someone switches on from the physical switch.
yes thats correct.
If so, Instead of a switch, do you think I could read directly the output from the thermostat? I need to check the voltage to not fry my ESP but in my mind it should work. To pass the Wife Acceptance Test she wants to be able to switch on and off from the old-fashioned wall thermostat.
Technically that is possible. But if you would like to use the old thermostate switch I would suggest going with the solution of @ AaronCake. setting up both relais in parallel does the magic. Your wife can easily, with the already known controls “override” the system. Still, HA would not recognize the state change. But we are in a scenario where HA is forsome reason not working…
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Connect your relay in parallel with the old thermostat. That way if the relay fails off, the old thermostat can always be used to control the system.
I think I am going to go for this one, although I find the idea of reading the old thermostat output super appealing hehe. I don’t know why I was thinking about series when it´s clearly in parallel (well I know, I suck at wiring). If it works (and it will) I may buy an 8 channel relay and do the same for the heating (I have underfloor heating). I have been postponing the project because I did not want to leave the rooms without the manual control (and I did not want to spend hundreds of euros in “smart” thermostats).
Sorry to re-open this. While planning the implementation I realize that the relay-in-parallel-set-up (attached diagram) gives you only half override. If one of the two is on (either thermostat or relay) the system is on. Thus, in case I lose connection to the relay and if the heating is on, I won´t be able to switch it off (unless I shut down electricity). It´s not terrible, but not ideal either.
The wiring should be more like a 3-way switch (I believe that´s the term in English, I mean one of those set ups in which two switches control one light). However I cannot think how to wire it that way. The control unit will be in the entrance, each of the old-thermostats are in one room, so I won´t be able to directly send a wire to them, I can only modify the connections. Any thoughts?
Sadly the 3way switch is not wireable, as I understand.
The actual location/wiring situation is not very obvious to me, but I understand that you could install the solution drawn out by you.
THe only “easy” way of solving this that I see at the moment is to wire a switch in series to the automatic relay. So you can shut off the function of the autmatic and then use the thermostat normally as you are used to. Switching on the power side requires a insulated and beefier switch but covers all the bases of µC errors as well as welded relay contacts.
