I recently purchased a simple condensate overflow safety switch (Rectorseal 97647) to install in my attic air handler unit. I currently have the switch installed on the red wire, but do notice the whole thermostat shuts off when the safety switch is activated.

I have a smart thermostat with the following wires hooked up:

  • G - fan
  • O/B - reversing valve
  • Y - cooling
  • C - common
  • R - 24V hot

My question is, should I wire the safety switch to the yellow wire or keep it on the red wire?

Will wiring to the yellow wire provide protection during heat mode or just during cooling mode? Is there risk of a condensate overflow during heat mode?

One final thing to note is that my thermostat has a A/C protection feature that delays powering back on the A/C after being turned off. As far as I can tell, that feature is preventing the A/C from turning immediately back on when the safety switch is deactivated.

  • 1
    What do you want your system to do when it detects condensate overflow in the pan ?
    – Traveler
    Commented Aug 11, 2022 at 0:26
  • 2
    That delay in the compressor starting is saving you the cost of replacing the compressor, be glad it is there.
    – Gil
    Commented Aug 11, 2022 at 2:29
  • @Ruskes, shut off the compressor, but leave the thermostat on.
    – James
    Commented Aug 11, 2022 at 4:59
  • @James, the interrup the Yellow one, that directs the compressor to run. Unfortunately it will also stop the heat exchange fan (air flow in your home.
    – Traveler
    Commented Aug 11, 2022 at 5:02

1 Answer 1


As you noticed the Red cuts the power to the thermosat and nothing works.

Yellow is probably the best choice it stops the compressor.

Unfortunately the yellow also controls the Air circulation Fan. You can turn on Fan-only on your thermostat to make it continue circulating the air.

When the Fan stops you will notice that and know you have problem with the high water level.

There is no condensation in Heat mode.

More automated mode is to install a very small sump pump and pump out the container when the switch activates it.

example: Pump

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