I need a relay to control a duct booster fan in my home (120VAC, 0.4A). I believe I found the fan wire from the thermostat (green), and I thought I read somewhere that it runs off of 5VDC. So, I need the 5VDC to trigger the 120VAC on.
What kind of relay do I need and where can I get it? I need something I can put in a regular electrical box. I have looked high and low locally, and no one sells them. I got this DPDT @ Radioshack today, but I am so confused by the additional leads, and I don't even know if it's okay to put this in an electrical box. Help?
12VDC/10A DPDT Plug-in Relay - RadioShack.com
What kind of relay do I need and where can I get it? I need something I can put in a regular electrical box. I have looked high and low locally, and no one sells them. I got this DPDT @ Radioshack today, but I am so confused by the additional leads, and I don't even know if it's okay to put this in an electrical box. Help?
12VDC/10A DPDT Plug-in Relay - RadioShack.com
yeah, I'd be looking for a solid state relay as well. They come in 5vDC control with switched part rated for 120VAC. They come with screw terminals ready to install. Not much more complex than wiring a light switch.
Does your thermostat actually send 5v out, or does it simply close a pair of contacts?
Does your thermostat actually send 5v out, or does it simply close a pair of contacts?
I don't actually know. I know right where the fan wire is, and it's just wire nutted. I called an HVAC guy to try and get some information and he said this is what he would do, so my understanding is that it does send out something.
When I started this project I thought it would be easier to figure out what to do. I can't find anyone that sells this sort of thing. I'm considering just buying the back pressure sensor from the fan manufacturer, even though it seems like a clunky solution to me.
When I started this project I thought it would be easier to figure out what to do. I can't find anyone that sells this sort of thing. I'm considering just buying the back pressure sensor from the fan manufacturer, even though it seems like a clunky solution to me.
Last edited:
Install a contactor in the HVAC unit that is triggered from the main fan or the fan output on the board. You don't want to run it off of the t stat otherwise ther will be no delay and the fan will run when the t stat closes and blow cold air unitl the main fan kicks on. This will aslo ensure that when the HVAC breaker is turned off there will be no power at the booster fan.
My uncle wants me to pull power right off the fan in the furnace. I'm hesitant about monkeying with the inside of the furnace. Would I just be looking for the power to the fan? My furnace fan has variable speeds.
Also, I didn't mention. The booster fan only draws .4A.
I have never heard of a contactor. This?
contactor 120vac - Product Details
Also, I didn't mention. The booster fan only draws .4A.
I have never heard of a contactor. This?
contactor 120vac - Product Details
That is a contactor. It is just a bigger relay. Many different versions available. You will want to connect the contactor coil to the hvac fan motor which will be 230 volts so get an appropiate one. Then you want to wire one phase to the contact and the other contact to the booster fan. The remaining lead will go to neutral since the booster fan is 120 volts. The neutral does not need to be switched. Run 14/2 romex from the furnace to a j box next to the booster fan and terminate. Install a fuse in the furnace for the fan.
My furnace is only on a 120V circuit... the controller board also says "120VAC" on it.
The fan is all buttoned up, but I have pretty good access to the controller board.
So, just intercept the fan power and neutral via the controller board? Everything is connected up with this type of connectors:
Terminal, Quick Conn, Blue, 16-14AWG, PK100 - Wire Terminals - Wire Connectors - 5X425 : Grainger Industrial Supply
The fan is all buttoned up, but I have pretty good access to the controller board.
An externally hosted image should be here but it was not working when we last tested it.
So, just intercept the fan power and neutral via the controller board? Everything is connected up with this type of connectors:
Terminal, Quick Conn, Blue, 16-14AWG, PK100 - Wire Terminals - Wire Connectors - 5X425 : Grainger Industrial Supply
There should be an output on the board marked blower or main fan. Connect the booster fan there or any point along that wire and the other to neutral. This will allow the booster fan to work in conjunction with the main fan. You can just cut the wire and wire nut them together. It is not a heavy current fan so it will be a simple tap in.
Last edited:
This is the one I am planning to buy. Grainger is close by and this appears to be right. If this is wrong, please yell!
Relay, Fan, 24 Vac - HVACR Relays - HVACR and Appliance Controls - 4E658 : Grainger Industrial Supply
Relay, Fan, 24 Vac - HVACR Relays - HVACR and Appliance Controls - 4E658 : Grainger Industrial Supply
Attachments
Aaaaaand a bunch of pictures. There doesn't appear to be just one fan wire. It might be a trick to find a fan wire that's just "on". It seems to have "cool lo", "cool hi", "heat lo", and "heat hi", which are all separate wires. However there is currently a jumper set on pins that say "heat lo" next to them. And I don't know what to use for the Neutral.
I don't have a scanner, but managed to take an OK picture of the schematic:
http://dl.dropbox.com/u/20886311/furnace_schematic.jpg
I don't have a scanner, but managed to take an OK picture of the schematic:
http://dl.dropbox.com/u/20886311/furnace_schematic.jpg
Attachments
Last edited:
The blower fan in the furnace runs on 120 volts. In your second picture you see five wires on the board. The white is your neutral. Use that for one leg on the booster fan. The blower most likely runs on low speed for heat and that would be the red wire.
If you have a meter then verify output when the main blower is running then you should have 120 volts at the red and white wires. Connect your booster fan there. If it is running at hight speed then it will be the white and yellow wires, Just verify how yours is set up with a meter while the blower fan is running. You will not need a relay.
Verify the voltage on the booster fan. It should be 120 volts. This will be a simple install. You will probably not use the booster fan for A/C since the A/C will run at a higher speed. This is just to get some extra heat to the far end of the trunk line to take the chill out of the room.
You don't want to connect it to the t stat as you may end up with feedback and the unit will not shut off and also the booster fan will run early and blow cold air.
You could wire it to the t stat with a delay relay and an additional contactor but that will be more complicated and will require a little rewiring of the furnace controls too. It will be easiest to just tap the main fan with the two wires I listed in pic two.
Test it and let me know what you find.
Brian
If you have a meter then verify output when the main blower is running then you should have 120 volts at the red and white wires. Connect your booster fan there. If it is running at hight speed then it will be the white and yellow wires, Just verify how yours is set up with a meter while the blower fan is running. You will not need a relay.
Verify the voltage on the booster fan. It should be 120 volts. This will be a simple install. You will probably not use the booster fan for A/C since the A/C will run at a higher speed. This is just to get some extra heat to the far end of the trunk line to take the chill out of the room.
You don't want to connect it to the t stat as you may end up with feedback and the unit will not shut off and also the booster fan will run early and blow cold air.
You could wire it to the t stat with a delay relay and an additional contactor but that will be more complicated and will require a little rewiring of the furnace controls too. It will be easiest to just tap the main fan with the two wires I listed in pic two.
Test it and let me know what you find.
Brian
118.3V from Red to White. The wire that looks white in the pic is actually grey, but I did find the white and it indeed goes to a pin marked neutral.
So then... I should just run 14-2 straight from the furnace control board to the booster?
One issue with what you said. We most definitely need the booster in the summer. Our bedroom (the room that needs a boost) is 90 degrees in the summer and 50 degrees in the winter. We'd like to split the difference there! The room literally has no pressure on it's vent. Because of that jumper being on "lo heat" do you think the fan always run's at that speed, or is that just a default?
I also do not want to cut the wires. I'll be searching for some sort of junction box or bus strip, I think.
And seriously thanks for the help. I owe you a beer, at least.
So then... I should just run 14-2 straight from the furnace control board to the booster?
One issue with what you said. We most definitely need the booster in the summer. Our bedroom (the room that needs a boost) is 90 degrees in the summer and 50 degrees in the winter. We'd like to split the difference there! The room literally has no pressure on it's vent. Because of that jumper being on "lo heat" do you think the fan always run's at that speed, or is that just a default?
I also do not want to cut the wires. I'll be searching for some sort of junction box or bus strip, I think.
And seriously thanks for the help. I owe you a beer, at least.
This sounds like the air flow has fallen out of design targets. Or was never set to design targets.
There is usually some form of adjustment in the airflow ducting and/or outlets to adjust the resistance. I suspect these need some attention.
The attic was popped up and finished in 1958. I think it is likely the home owner did some of the work, or standards just weren't the same. In addition, the insulation probably isn't very good up there. As I said before, this duct line is at the very end of the main trunk. It twists around a bunch before heading upwards, and it's only a 6" duct. I don't think there were ever design targets. If ever we can afford to remodel the house, these issues will be fixed, but there isn't much I can do now. I have opened or closed every baffle trying to get some air to flow up there and nothing works. Our neighbors had this same issue (same style of house) and a duct booster helped them a lot.
P.S. my brother's name is Andrew T, so I thought you were him when I first saw this.
P.S. my brother's name is Andrew T, so I thought you were him when I first saw this.
Last edited:
That's the duct I am boosting.
I think I'll use something like this to connect the wires up.
Connector, Pk10 - Terminal Block Accessories - Terminal Blocks - 6YH84 : Grainger Industrial Supply
Terminal Strip, 4 Pole, 20A, .437 Spacing - Terminal Blocks - Terminal Blocks - 6ZEG8 : Grainger Industrial Supply
Attachments
You can make a pigtail with some 1/4" quick connects so you can plug it into the board, plug the fan wire into the pigtail, and the other fan into the pigtail. You can install a 3 way wall switch in a box on the outside of the furnace so you can connect the fan lead to the switch common and the other two terminals to the heat and cool outputs on the board. Then you use the switch for summer and winter mode. If you want to remove it then you just unplug the pigtails, reconnect the fan wires directly to the board and it is then completely stock without cutting any wires.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.