Honeywell Prestige IAQ Kit YTHX9421R7001WW


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Old 07-24-22, 02:34 PM
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Honeywell Prestige IAQ Kit YTHX9421R7001WW

Hello members. I've decided to pull the trigger and replace my current thermostat with a Honeywell Prestige IAQ EIM kit. I really like the idea of combining the furnace/AC, humidifier and HRV into one cohesive system. It's a little daunting at the moment, but I think I have the skills, understanding and perseverance to get it done correctly. I just need a little help with the wiring to be sure I don't damage anything or incorrectly connect any of the components. Here's my current setup:
  • Bryant 350MAV048100F furnace with AC - single stage w/ wall mounted Honeywell smart T-stat (5 wire)
  • Bryant HRVBBLHU1250 ventilator w/ wall mounted basic controller (4 wire)
  • Aprilaire 600 humidifier w/ utility room controller
Looking to replace it with the Honeywell YTHX9421R7001WW kit that includes these components:
  • THX9421R5021WW Prestige 2-Wire IAQ Thermostat
  • THM5421R1021 Equipment Interface Module
  • THM6000R7001 RedLINK Internet Gateway
  • C7089R1013 wireless outdoor sensor
  • C7189R1004 wireless indoor sensor
  • 2 Duct Sensors
I think I've got the connections between the EIM, furnace and humidifier mostly figured out, but I'm a little confused with getting the HRV connected. It looks like my furnace supports the low speed fan dehumidifier (DHUM) function so I'd like to utilize that too. I sure would like to learn how others would connect these items. Here's my current setup that I'm looking to replace with the Honeywell:


My current setup

My challenge is to attach this gear to the Honeywell EIM:


My setup is obviously different. Single stage of heating and cooling, but with humidity and a HRV

Sure would like to see how the pro's out here would accomplish this. A wiring diagram would be tops! Thanks for any help you can provide!
 
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Old 07-24-22, 04:22 PM
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Do you want to eliminate the HRV controller and have the IAQ control the dehumidifier ?
It would connect to the U1 terminals.

Your humidifier doesn't appear to be drawn in-correctly.
What you have labeled as humidifier should be humidistat.
The HH terminals are only a switched contact. No power comes out of them.
What model humidifier are you using ?
Do you want to eliminate the humidistat and use the IAQ to control the humidifier ?
The humidifier would connect to the U2 terminals.

Work in progress......................


 
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Old 07-24-22, 06:44 PM
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Hey PJmax - thanks so much for your response and willingness to help me out! I'll try and answer all your questions in order.

Yes, I would like to eliminate both the HRV controller and the humidity controller. My desire is to have the new Honeywell do all that work, and be able to program it to be as smart as possible with all four areas of IAQ (temperature, humidifying, dehumidifying and ventilation). Are you inferring that the HRV is a humidity control device? My understanding is that an HRV only controls humidity to a certain extent and that it's more of a ventilation device during the Winter (I live in MN). I wish it was an ERV instead, but the HRV came with the house, so that's what I'm working with. Hence my desire to use the furnace's low speed fan dehumidifying function (DHUM) during the Summer. Yes, I'd like to have the EIM control the HRV via the U1 contacts, but I am unsure of how to wire that correctly. I think I'm letting the current wiring confuse me because the blower is set up to run when either the thermostat or the HRV controller calls for it (using that relay) - that's my one big head scratcher.

Hmm. My humidifier is an Aprilaire 600 (not 600A). Currently the H terminals go out to the water
solenoid with no other connections. The unit is powered by the furnace EAC1 and EAC2 terminals so those H terminals must be supplying voltage to the solenoid:


I'm thinking if I rid humidity controller the water solenoid will go to the U2 terminals on the EIM along with a 24V source in series, allowing the new Honeywell stat to control when humidity is applied. I could use the existing 24V transformer and wire it like this:


I could even take the transformer 120V input off the EAC1 and EAC2 connectors of the furnace control board and simply wire it to 120V permanently. Am I thinking this through correctly?

I hope I'm not throwing confusion into this discussion. I really want to know the inner workings of this whole project and know for sure it get installed correctly while using all of the functionality possible.
 
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Old 07-24-22, 09:44 PM
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Regarding connection to the HRV - will the EIM (U1 terminals) need to connect to the override switch contacts on the HRV control board? Outside of this, I just can't see how the EIM can connect to the HRV.



Here's the manual for the HRV in case you can't see the above highlighting very easily:

https://docprime-x.com/view/1561275/...ons-manual-24/
 
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Old 07-24-22, 10:07 PM
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And finally, the connection for the low speed fan dehumidifier (DHUM) function on the furnace. Last pair of EIM contacts (U3) to use. Would I simply connect the DHUM on the furnace to the EIM U3 contacts with a 24V transformer in series? I'm pretty sure my furnace expects no voltage on the DHUM terminal to dehumidify. 24V on the DHUM terminal = no dehumidify. Regardless, I know I can change the functionality of the EIM U contacts to normally open or normally closed within the tstat setup. Which makes me wonder, since there is no connection to the DEHUM terminal at present, does this mean my AC has always been running in dehumidify mode all along? Also, I've read in numerous places that the J1 jumper on the furnace control board should be removed when using DHUM function - it's presently connected to the 120 second poles.


 
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Old 07-25-22, 07:13 PM
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So I went on a fact finding mission regarding my HRV. After fully digesting the install manual here's what I've found and tried regarding the wall controller and the bypass switch (contacts OL and OC on the HRV control board).

The bypass switch calls for ventilation regardless of the HRV wall controller settings. If the wall controller is disconnected the bypass switch functionality still works (in lieu of what the manual says). Regardless if the wall controller is attached or not, and also regardless of whether the wall controller is presently requesting ventilation or not, or even if the wall controller is turned off, here's how the bypass switch works:

1) If the bypass switch is momentarily pressed (touch OL and OC together momentarily for about 1 second), the HRV opens the damper and its blower runs for 20 minutes, then the blower stops and the damper closes. The 20 minute timer is located on the HRV control board.
2) If the bypass switch is pressed and held (again, touch OL and OC together) longer than momentarily, the HRV opens the damper and its blower runs continuously. Once the bypass switch is released the blower stops and the damper closes immediately, without any 20 minute timer involved.
- In either scenario, if the wall controller is connected and is still requesting ventilation it will continue to ventilate until satisfied. Once satisfied the wall controller will turn off the blower and close the damper.

This satisfies me that I can control my HRV with the EIM, with or without the HRV wall controller connected.

Note: It's imperative that I'll need to keep the HRV interlock relay circuit in-place to be sure the furnace blower always operates when the HRV ventilation is called upon by the EIM.

Further note: If I want to ventilate/circulate air without the HRV and its open damper (for instance when it's overly humid outside) I can simply turn on the furnace fan with the thermostat. I'm pretty sure I can program the Honeywell thermostat to take all this into consideration and perform the functions desired and required.

I'm now feeling pretty good that I can get everything wired correctly and configure the Honeywell thermostat correctly too.
 
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Old 07-25-22, 09:21 PM
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Hey Pete, I have a question I hope you might be able to answer.

Regarding using the EIM to control the humidifier/water solenoid. Without looking at my idea of simply connecting the water solenoid in series with the 24V transformer then to the contacts of the EIM relay, is there a different method you would use to control humidity with the EIM? I ask because I got to thinking about the inductive kick that occurs when a relay opens when driving a solenoid, and the potential of arcing at the relay contacts. I sure don't want to damage the EIM relay because of something like that.

 
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Old 07-25-22, 09:49 PM
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I've never come across a problem caused by the solenoids.
You could probably put a capacitor across the solenoid to suppress the spike.
I could check into that.
 
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Old 07-25-22, 10:27 PM
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Okay, good to know - thanks

I've been refreshing myself about what is known as snubber circuits that go across the relay contacts. I've actually been scrutinizing the circuit board of the EIM near each of the miniature relays and I think I see where they're using a snubber circuit for each relay. Simple and inexpensive prebuilt snubbers are available on eBay or Amazon too - I might just order one since I'm already ordering a new 24V 40VA transformer anyway:

https://www.amazon.com/PoityA-Absorp.../dp/B07TV3R3T1

 

Last edited by Nortonics; 07-25-22 at 10:48 PM.
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Old 07-25-22, 10:47 PM
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That blue part is a varistor or similar and does the spike suppression.
The resistor is probably inline with the varistor to protect the circuit if it shorts.
Varistors

With DC.... a simple diode across the load is all that's needed.
 
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Old 07-26-22, 07:09 AM
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Well, I think you're close and have the right idea. Here's that snubber device as installed in-circuit:

Looks like perhaps the manufacturer has incorporated two levels of snubbing to cover both AC and DC circuits? I can't say diddly about the component values though as the math gets intense, so I'll take his specs at face value. I can just barely see a 70 volt value on that varistor, which is certainly better protection than the potential 1000+ volts of induced EMF from a solenoid kick-back upon opening the circuit/relay.
 

Last edited by Nortonics; 07-26-22 at 07:28 AM.
 

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