I added a new room on my home and am adding a 3 amp booster fan to my a/c unit that will turn on and off with the blower fan on the main unit. I can pick up a relay to be used to switch it on and off but my question is what would be the best place at the a/c unit to power on the relay from? The model on the unit is WCY036F100A and it's an American Standard/Trane. I have the wiring diagrams for it and just need someone familiar with these units to point me in the right direction!
Also any suggestions for the relay type would be great too.
Thanks

I have no wiring diagrams for that unit so it will be difficult to help you.

Post the wiring diagrams and we will see what we can do.

Thanks for checking it out.
Dale

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I would pick up a signal circuit off (F) which is the fan control in the unit. If you can find a low voltage (24 volt)signal that is good(triggers when the blower in the outside unit comes on) then all you will need to do is pick up a common with that to make a complete trigger circuit for a relay in the house close to the booster blower. The relay inside would have a 24 volt coil and what ever power terminals you need. (Normally open will work) This way when the unit blower motor comes on for the air to blow inside it will send a signal to the inside relay to also come on.

Now a word of caution. You might end up having to use a 240 volt signal circuit for the indoor blower motor on the outside unit. If that is the case you will need a 240 volt relay coil and a normally open relay. This way when the relay makes it will send a signal only to the inside with no voltage. Then inside you will have to use a small 24 volt transformer in combination with a relay circuit to kick the small interior fan on. The outside relay will close and act as a switch which will allow the coil on the indoor relay to close to start the smaller motor.

The first type set up is the easiest if you can find a 24 volt circuit that activates the relay for the outside motor as you can tell by the extra transformer and relay that the second set up will take.

Please do all wiring in a safe manner and fuse the circuits with small fuse assemblies that you can get at Radio Shack. Calculate the fuse requirements by the size of the VA of the transformer you get.

BTW use at least 18 gauge wire for the signal circuit to prevent voltage drop .

First off, thank you for a quick response!
Second, I liked your idea of the first solution so I found a 24 volt switched circuit off the fan relay and it switches with the blower motor. It even has a pigtail hanging off the wire already with what appears to be the factory crimp on wire nut. The only thing about this connection is that the 24 volts is only good up until the compressor switches off and then the voltage is gone but the blower still runs for a couple of minutes and then it turns off also. That was the only point I found to get the 24 volts switched, do you think it will be an issue? I don't care if the booster doesn't run for the extra 2 minutes or not because of the delay circuit.
Does it matter whether I pull the common from a particular place or is using the main ground on the unit sufficient for the relay?
I will be going back to the unit again and try locating the fan relay tomorrow morning when it is much cooler.
Thanks for your help.

You tapped into the fan delay circuit. That will work but as you said it will run for a minute or two after the unit turns off. The main blower for the house also runs for a few minutes also so I see no problem..

Since you have to bring two wires into the home for the switch circuit it would be best to go to the source for the neutral. This way nothing is being overburdened. The main ground will work if you cannot find another source. Put a small fuse in the circuit also to take care of any shorts in the wiring that may happed. A twist apart automotive fuse holder with a very low amp fuse will do the trick.

Thanks for the help HVAC1000! The booster fan works great. I fused the relay connection at the main unit with a .5 amp fuse. Do you think it's a good idea fusing the 3 amp booster fan motor as well? If so would you use a 3 or 4 amp fuse? The reason I ask that is because it's getting it's power from a 20 amp outlet.
BTW, I never was able to find a 24 volt tap that was part of the delay circuit which keeps the blower running after compressor shutoff, do you think the delay is built in to the circuit board somehow?
Thanks again for all your help.

Yes it would be a good idea to fuse the booster fan itself. With out one the fan motor could get hot and go up in smoke in case of a failure. Good Idea

When I looked at the diagram I thought the tap could have been made off the delay but you are there and I am not so you can tell the conditions much better that me.

Glad you it it going.