I am designing a system to mist my outdoor air conditioning units during the summer. I will be powering a low voltage irrigation value using the low voltage from the AC controls - 24 VAC. I have 2 air conditioning units that work independently of each other. However, there will be times that both units come on at the same time.

How do ensure when both units come on at the same time that electricity is sent to the power power supply without shorting out the solenoid or shorting out the air conditioner power supplies?

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  • \$\begingroup\$ Use two irrigation valves, one for each air conditioner. \$\endgroup\$ – Peter Bennett Jun 27 '16 at 19:22
  • \$\begingroup\$ Yes. That would work. Trying to just use one valve if possible. Thanks for the reply. \$\endgroup\$ – Dan Huber Jun 27 '16 at 19:50


simulate this circuit – Schematic created using CircuitLab

Figure 1. AC source switching.

How it works:

  • If AC1 (supply 1) is off the relay is de-energised. If AC2 (supply 2) turns on it is passed through the normally closed contacts of the relay to the irrigation valve.
  • AC AC1 turns on the relay energises and AC1 supplies the irrigation valve.

You need a relay with 24 V AC coil and contacts rated at 24 V AC/DC minimum and rated at the switching current or greater.


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