HVAC Logic Gates

Thread Starter

elmetal

Joined Dec 14, 2017
7
Hello guys,

so I have 3 wires all 24VAC that I need to setup a system of logic gates for.
Wires A B C only get 24V when the respective system is powered (A = Heat, B = Fan, C = Air conditioning, D = Common (24VAC always on))
I am thinking relays since it is 24VAC.

Here's what I need in text form:
We'll call it wires A B C D
If (A or B is 24V) AND C is 0V then output 24V from D to the new device

That's it. If either the Heat or the FAN is on, then output power but only if AC is not on!

Hope that makes sense.
 

ScottWang

Joined Aug 23, 2012
6,963
I was drawn the logical control diagram to shown the conception that you want and we can try to use the bjt or logic ic or relay or mix them to reach your requirement.
OrGate_Inverter_ANDGate_elmetal_ScottWang.png
 

Thread Starter

elmetal

Joined Dec 14, 2017
7
It looks good! Now comes the hard part, finding 24vac components.

I live in Denver so we have microcenter and allied electronics to my knowledge.
 

Thread Starter

elmetal

Joined Dec 14, 2017
7
The main requirement really is longevity and price. I don't mind soldering components and such. I just want something I can set and not worry about ever breaking (not for a few years)
 

be80be

Joined Jul 5, 2008
2,049
Lol like i said you reinventing the wheel

Just make sure you get the right one they come in 24 volt made for what your doing
you get heat AC and fan
 

Thread Starter

elmetal

Joined Dec 14, 2017
7
Lol like i said you reinventing the wheel

Just make sure you get the right one they come in 24 volt made for what your doing
you get heat AC and fan
I'm not reinventing the wheel... I'm trying to turn on something but only when fan or heat is on, not AC
 

be80be

Joined Jul 5, 2008
2,049
Those are 24 volt and the come like you want they come in the same combination
as crutschow drew up in his post all in one black box.
24 volt ac coil and all
And they sale then at any good AC supply house

I don't now where your at but I live in ky probably 10 store stock them.
but they come in spdt and up you can get them that do most anything you'd need
or get 3 and do it like crutschow drew
 
Last edited:

shortbus

Joined Sep 30, 2009
8,057
I don't now where your at but I live in ky probably 10 store stock them.
but they come in spdt and up you can get them that do most anything you'd need
or get 3 and do it like crutschow drew
And also as close as the local Graingers, even if it means buying from the internet.
 
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