Air Conditioning - How to wire a flood switch to shut off BOTH A/C and furnace?

I have a condensing furnace with an AC coil in the attic, and I want to add a wetswitch to cut off the HVAC if for some reason the drain fails and water collects in overflow pan.

The wetswitch instructions suggest placing the switch in the wire that powers the AC condenser contactor - but I want the switch to also shutoff the system in case the furnace condensate starts dripping, so I want the switch to shutoff both the furnace and the AC whenever moisture is detected.

How do I wire in the switch to accomplish this?

Thanks!

use the switch to control a relay or contactor where both the AC and furnace circuits run through it.

use the switch to control a relay or contactor where both the AC and furnace circuits run through it.


Would that be the R wire that goes from the transformer to the thermostat?

If this switch is a two wire switch, then yes, put the switch between the R at the furnace and R at the thermostat.

That way if the switch trips, the power is cut off (R) to the thermostat.

If this switch is a two wire switch, then yes, put the switch between the R at the furnace and R at the thermostat.

That way if the switch trips, the power is cut off (R) to the thermostat.

Jay, thanks. Page 2 of the wiring diagram (http://www.diversitech.com/applications/documentlibrary/documents/WS-1%20-%20Wet%20Switch.pdf)on the wetswitch recommends cutting the common wire from the transformer, instead of the red. That would have the same effect, I believe, of cutting off whatever equipment is being used (AC or furnace), right?

Ok, with that style of switch, it depends on how the thermostat is wired up.

If there is no C hooked up, and runs on battery, the switch is not going to do anything for heating, it will only kill the outdoor unit.

If there is C hooked up at the thermostat, and is not using battery, then it will kill both.

Thanks Jay! I do have C hooked up at the thermostat. So that's the Common wire I should be splicing the switch into, correct?

Yes, the C wire to the orange wire of the switch, not to the furnace's C.

I take it you have no battery in the t-stat?

Yes, the C wire to the orange wire of the switch, not to the furnace's C.

OK, makes sense. That's what I was thinking, thanks for confirming.


I take it you have no battery in the t-stat?

It's a VisionPro, and it has 24AC wiring as well as battery backup.

It's a VisionPro, and it has 24AC wiring as well as battery backup.
There is two types, the factory built in, and the AAA battery that can get changed..

The AAA needs to come out, the factory one stays, and that just keeps the program in place. The AAA is the one the "runs" the t-stat if common wire is not there.

Yes, I believe that I only have the factory Lithium backup battery installed, and not the AAA ones, but I'll check it tonight.

Thanks!

Jay,

The more I read about thermostat wiring, the more I think that it makes more sense to cut the red wire, which would power off everything and anything if the circuit gets interrupted by the wetswitch. Seems like a more logical wire to cut than the Common wire. Do you agree?

I agree on the red wire....never had to make that decision in an attic situation, but I tell customers that if they leave for extended periods that condensate is going to make less of a mess than water lines that have burst.

With that switch you got, you can't kill the red wire.. it has to stay on the common side of the system. How ever, we can "rewire" that switch to work the the way that Tinman and I agree on.

I agree on the red wire....never had to make that decision in an attic situation, but I tell customers that if they leave for extended periods that condensate is going to make less of a mess than water lines that have burst.

If I read you right, you are referring to the concern of an attic furnace that shuts off due to condensate leak, letting the house cool down to the point of pipes freezing and bursting inside, correct? Must say that I hadn't considered that, it is a good point. We never get below freezing here, so it's not a concern for me (if I understood you right), but thanks for the comment - it makes a lot of sense.

With that switch you got, you can't kill the red wire.. it has to stay on the common side of the system. How ever, we can "rewire" that switch to work the the way that Tinman and I agree on.

I see what you mean - with the red wire cut, the switch will lose its "smarts" for the LEDs, right? But if I cut the C wire instead (and assuming there are no batteries in thermostat), will that kill either condenser or furnace if the switch opens? I guess it would interrupt the transformer circuit (?).

Actually, I think I understand why I was confused - if I cut the C wire, I should not be cutting between the circuit board and the t-stat, but between the circuit board and the transformer, correct?

With that switch you got, you can't kill the red wire.. it has to stay on the common side of the system. How ever, we can "rewire" that switch to work the the way that Tinman and I agree on.

Jay,

Just wanted to say Thanks, and to report that I did rewire the switch (actually two of them, since there are two pans), to interrupt the red wire to the t-stat in case of flooding. I have also wired in an inline condensate line switch (EZT-225), so it was quite the wiring party :) .

But it all works now, actuation of either of the three switches kills the system, as intended.

Thanks!

Glad to hear you got it figured out, and working as lot of us like to see it be.