I have a residential Honeywell Prestige IAG system, with THX9421R5021 thermostat connected to a Honeywell EIM. I want to wire a relay (which I'll connect a dry sensor to) to the EIM, that will allow me to determine when the blower fan comes on.

Reason: I have a Fantech FG6 Duct fan installed at the end of a very long duct run. Currently I have to manually turn it on/off with a switch. I want to automate this via my SmartThings Home automation system. If I can get a relay with a dry contact wired up to the EIM, I can plug a smart dry contact sensor onto it, and then automatically turn my fan off and on.

I've attached an image of my EIM. Does anyone know what leads I can wire off, and possibly suggest what sort of relay with a dry contact I could use to connect. I would actually like the relay to indicate whenever the fan comes on (cooling or heat), but if that is not easily doable, I'm really most interested when the thing is in heating (blowing hot air) mode.


Thank you!

 

When I add a duct booster fan to a system I use a current sensing relay around the high voltage common wire to the blower motor. It is often necessary to loop the common wire through the relay a few times to meet the minimum 4 amps required to close this relay.

There is a high voltage model 51 and a low voltage model 50. If the booster is close to the furnace I would consider the high voltage model but if the booster is far from the furnace ( and there is another possible source for my 120 volts) I would use the low voltage model 50, a j-box and a fan relay.

 

Too bad you can't program the Honeywell thermostat/EIM to use the U1 relay.

How about a simple fan relay (https://smile.amazon.com/gp/product/B00BTLN78Q) driven by W and C? That would trigger on heat. Add a second relay driven by G and C for a/c (fan). Then put the contacts in parallel so that if either was called the dry contacts will be available to your sensor.

Otherwise if you have a gas furnace see if it has an EAC/electronic air cleaner terminal. Usually 120v but might be 24v.

In the end a SmartThings solution is shaky as it really overcomplicates things. Better to get a real two wire cable to where the duct fan booster is located.

 

Thanks for the replies. Unfortunately, the booster fan is too far away (basement vs 3rd floor), and in an obscure location, to be able to get wiring from it to the furnace. Thus, I'm left with looking for other alternatives.

I too was hoping to use the U1/U2/U3 dry contacts. In reading (HVAC stuff is ALL new to me) they can be setup for ventilation, humidification, or dehumidification. U1 is already setup for ventilation, and has something connected to it. I was thinking that if I could program H2 for humidification, and program it to be on ANY time heat is called for, that might work, but not sure if I can program it that way in the thermostat Advanced settings.

The furnace is a Trane XR95, and in Googling, appears to indicate it has an EAC terminal on it. So, if it does:

1) Would I be better using that (I think that is 110v) or using the relay you suggested and connecting that relay to the W and C on the EIM?

2) Could you recommend a 110v relay that I could use if connecting to the EAC, or is it the same relay you recommended?

3) Do you know if the control board where the EAC would be located is easily accessible if I remove the front cover to the furnace?

Sorry, I'm new to this. Thanks guys, for sharing your knowledge!

 

1) could go either way. Since you are are a novice, using smartthings and not traditional HVAC controls I would use relays from the EIM. Mainly to keep you away from line voltage.

2) Different relay as the EAC terminals are 120vac. You could use a relay such as https://www.amazon.com/Functional-De.../dp/B000LESCI2 since it will use 120v or 24vac.

3) Should be easy to get to. Trane might have EAC wires marked and capped at the electrical junction box. Otherwise use crimp on insulated spade terminals for the line voltage and then it should be a direct connect to the board's EAC and neutral terminals.

 

Awesome, thanks for the link to the relay! That looks pretty inexpensive, and fairly simple to do, if I can find the EAC terminals! I'll give it a go!

 

OK, I've found the EAC terminal on the board. Unfortunately, there is only a single EAC terminal. Where do I connect the other lead from the relay. I've attached an image of the Board and the EAC terminal. Thanks!

 

There are two EAC terminals.

That one in your picture is labeled EAC-N..... N for neutral.
There will be a second one labeled EAC-H... H for hot.
(Looks like you already have something on EAC-H.)

 

Thanks! You were exactly correct! It was indeed in the upper left corner. It was the black wire just below the yellow wire. They had already plugged in a wire (nicely labeled EAC) that ran to the junction box, and was dead-ended there. Tested voltage across both EAC terminals, and it shows 120v whenever the heating or cooling mode turns on the blower. This should work perfect. Thanks everyone for your help! This forum is awesome!