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Author Topic: Furnace Relays  (Read 4830 times)

Offline lkwilson

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Furnace Relays
« on: February 17, 2009, 11:10:02 AM »

The documentation with my furnace states that it has three available dry contact relays (no power supplied from board).  The relays switch whenever the blower motor is operating.  These relays can be used to interlock humidifiers, air cleaning equipment etc.  Power (if required) must be supplied to common from an external source.  Max voltage - 120 volts.  Max Amperage - 10 amps.

I want to hook up an HRV that runs only when the blower runs but am unsure how to hook it up.  The diagram shows a wires connected to relay connections NO and Com.  Would this be the hot wire coming from my circuit panel to the HRV?  Any help would be greatly appreciated.

Lifebreath Clean Air Furnace

Offline Repair-man

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Re: Furnace Relays
« Reply #1 on: February 17, 2009, 02:20:25 PM »
A circuit which is labeled "N/O" means that whatever is connected to it will not run unless the relay is energized. In other words, your fan is also set up on a N/O relay switch. It closes when the fan relay is energized.

Placing a device on the N/O and the incoming hot lead on COM will assure that the device receives power when the realy is on. The other leg of your device goes to Neutral or L2, depending on voltage. I have no idea what a HRV is.

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Offline lkwilson

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Re: Furnace Relays
« Reply #2 on: February 17, 2009, 03:13:06 PM »
Thanks for the reply, I was hoping that was the way it worked.  HRV is short for Heat Recovery Ventilator or heat exchanger.  It brings in fresh outside air and exhausts stale air from inside the house.  It uses the air being pumped outside to warm up or cool down the air coming in depending on the season.  Thanks again.


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