Nest Thermostat Gen 4 - Ventilation (HRV) Wiring Question

[DancingKangeroo]

Hi all, thanks in advance for your help. I'm investigating whether I can hook up the 4th gen thermostat to my home. I have standard furance / cooling set up which the compatability had already cleared (R, W, Y, G, and C). However, my home also comes with a ventilation unit (HRV). Based on the manual I'm seeing two wiring diagrams as follows:

Single Speed HRV Wiring (High Speed)
Low - N/A
Hi - ACC1 / ie. AQ+ (?)
ON - (short with red)
Red - ACC1 / ie. AQ- (?)

Two Speed HRV Wiring (Low and High Speed)

Low - ACC1
Hi - ACC2
ON - (short with red)
Red - ACC1 & ACC2

Would it possible to hook up the two speed or is the 2-wire ventilation compatability mean purely putting AQ+ and AQ- on the high speed single mode or is there some alternate wiring I can do to utilize the * as well? Thank you! 

Ventilation (HRV): Lennox HRV5-150

Source: https://tech.lennoxintl.com/C03e7o14l/VIu12Ch2uV/507363-04d.pdf - page 14 

[luciaaa]

Hi, @DancingKangeroo,

Thank you for reaching out to the community and for sharing your investigation. I'm happy to assist you.

As you've correctly determined, the Nest Thermostat 4th generation is indeed compatible with your HVAC system. However, the specific wiring configuration for your ventilation system requires professional expertise. I highly suggest you contact a Nest Pro technician or a qualified HVAC technician so they can accurately identify and connect the wires to ensure optimal performance and safety.

Please keep me posted.

Best regards,

Ana

[Dilon_V]

Hi there, I have a similar setup. Were you able to get the HRV to work with the Thermostat?

[DancingKangeroo]

Hi Dilon_V! Yes, I got it to work. I did reference older posts from ecobee forums (and tried a google support suggestion). Findings:

1. Depending on your HRV, you will have to follow the manual for single speed (timer) wiring. For me, it was connecting AQ+ and AQ- to either High (or Low) and Red. My particular model require I also add a connection on the HRV between ON and Red as well. This is my current set up and everything works.
2. Google chat support suggested if I wanted to try the two speed wiring to utilize Y2 and * as well. I did try this initially but Nest Thermostat said one of the wires was missing power. Without further support and short of asking a professional, I stuck with #1. 

Hope this helps!

[Dilon_V]

Hi DancingKangaroo,

Thank you so much for getting back to me. Wanted to ask you what you meant by "Red". Is this the "Rc" on the Nest?

Thanks again!

[DancingKangeroo]

Not a problem! And Red is on your HRV (at least my model). I would have to suggest reviewing your HRV manual. 

Here's an example of what I referenced for my model (Lennox HRV6-150): https://tech.lennoxintl.com/C03e7o14l/VIu12Ch2uV/507363-04d.pdf / page 14