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Aux booster fan cant find connection

Posted by tommedlin (My Page) on
Sun, Oct 20, 13 at 16:43

I have a an Air conditioner/furnace and needing to connect a booster fan to it. Duct work is run to the location and i have installed a 120 v booster blower and a 24v Electric damper. I am an Electrical engineer but having trouble following the schematic in the furnace. So here is what i need to do. I have installed a switch in my shop which will turn on the 120 v fan and also a 24v transformer (which opens the damper). I was trying to connect this 110 v line to the hvac unit where when the blower came on, (and i had the switch on in the shop) then the damper would open and the booster would run. By having the switch in the shop, I would only turn it on when i was working there. I have attached a schematic. I can not seen to find a single place of 110 v that comes on when the hvac blower is on. I know that you have high speed blower for Air and lower speed for heat. Seems i cant find a common point for 110 ac when either fan is running.

I have even looked at the hvac 24 volt system. I understand the green wire is for fan but is that on for both heat and cool? If so i guess i could install a 24 volt relay which could control the 110 to my aux booster.

can anyone tell me the best , easiest way to connect to a point in this furnace where i will have a voltage if either heat or cool blower is running? Thanks, Tom


Follow-Up Postings:

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RE: Aux booster fan cant find connection

Connect the booster fan supply wiring to the point where your air handler fan receives it's power. If the air handler is multispeed, do not follow my suggestion.
Engineer? Really?
If you want the damper to operate at the same time, use a 24 volt transformer near the booster fan and power the damper from that.
Engineer? Really?


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RE: Aux booster fan cant find connection

Additionally, if the air handler fan is two-speed, two line-voltage relays could be used to operate the booster fan. One of the relays would have the operating coil powered by the fan power for one speed and the contacts would supply line-voltage power to the booster. The second relay operating coil would be powered by the other fan speed. Properly connected, the two speed function would work perfectly and only one relay would be energized at a given time.
I have never done such a hookup. So be your own judge.
I do not have degree in Electrical Engineering. But do have some course credits.
Modern electronics may offer other solutions.


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