I have a self standing HVAC unit that has a control panel with manual buttons. There is no thermostat. Eventually my goal is to create a relay that can be controlled via IR/RF so I can install a Nest and control my HVAC units remotely. But this question is simply about trying to debug the manual interface and figure out how to add the relay to the system so I can turn on the heat.

For simplicity, assume I have one button on this control panel:

And here is the backside of the control panel (top left of image is where the buttons are on the front):

How can I install a relay to control one of those buttons?

My guess is that I should use a voltmeter to figure out how the metal terminals on the back of the button part map to the buttons, and then install a relay across one of those terminals.

I have a self standing HVAC unit that has a control panel with manual buttons. There is no thermostat. Eventually my goal is to create a relay that can be controlled via IR/RF so I can install a Nest and control my HVAC units remotely. But this question is simply about trying to debug the manual interface and figure out how to add the relay to the system so I can turn on the heat.

For simplicity, assume I have one button on this control panel:

And here is the backside of the control panel:

And here is the wiring diagram on the unit:

How can I install a relay to control one of those buttons?

The wiring diagram is a bit strange, for example, I see that High Heat = 1->1A 3->3A 4->4A 7->7A and 8->8A closed, but there are no leads on some of those terminals (1A, 4A, and 8A have no leads?)