Lennox Control Board Wiring Diagram

[Anais Wachowski]

HelloSeton,

Thank you for the clear graph and it really helps a lot. I have the exact furnace + AC combo as you do. Couple question regards to your graph and set up,

-From the SLP98V manual, for a 2 stage Heat/ 2 stage cool set up, the graph is missing the G wire from the control board to the Nest. Do you leave it out on purpose ?If so how did it go without the fan control?

-I know you need to set the board to non-communicating mode, may I know how exactly you do it? Which DIP switch you need turn on/off, and anything else you did on the board for it to work?

I want to thank you all. I have a Lennox ML180UHE furnace, with an AC condenser outside. After reading these posts I got brave and went up to the attic. My furnace has your standard W-C-G-Y-R plugs, and they had wired those 5 wires out to another box, which then turned the signal into the C-R-I+,I-, requiring the communicating thermostats.

The issue I did have, I must not have been too careful with the power, because I took off the thermostat after it was working, hung it on the wall, and plugged it back in, and the entire system was dead. After an hour of searching and cursing, reinstalling the old setup to no avail, I figured out it was the fuse, and popped in a new fuse and it was good to go.

My iComfort thermostat shuts off at night. I want to replace it with a Nest 3rd generation thermostat. I checked the connection of the indoor and outdoor units. The wiring ports look the same as what was posted by @Seton_Carmichael. I have some questions:

I have no experience in HRV, just some simple DIY weekend stuff. Any advice on how to tie in the 3 wired HRV to all of this, and the functionality difference between the 2 wiring diagrams?

@bade011 any feedback?

My icomfort wifi display just died. I also have a single blower system. Are new wires necessary? Could you install a new Nest thermostat with the existing 4 wires by disconnecting those wires from the Lennox control box and rerouting them to the furnace board directly?

I am trying to install my Ecobee3 now. After finishing the connections, Ecobee did not power up. I did some reading and I believe the C-wire, though it is available is not connected to the power at the furnace-end (see the picture where you can find the blue standalone wire). Can you please suggest where/how I connect the C-wire in my furnace (model # lennox g12q4-110) to supply power to the Thermostat? Thank you very much for your help in advance.

I have this exact same furnace (30+ years old) and very similar messy nest of wiring. As user76730 noted the yellow on the 24V side of the transformer is the key. In your photos, this is the left most wire nut that is pointing up with 2 yellow wires and a green attached. I had a spare blue thermostat wire from my old Honeywell mercury blob setup that was completely unused and just wrapped back in the wall. Hooking that up to the yellow bundle and then the C terminal on the thermostat is working like a charm. I have a Nest E with just the R and W, and it was power stealing badly. Now it runs very smoothly.

The pictures are a little difficult to follow but according to the electrical diagram there is a blue and a yellow wire coming off the low voltage side of the transformer. Connect the C wire from the thermostat to the yellow wire from the transformer

I also have the Lenox G12Q4-110 furnace (heating and cooling) system with a four conductor thermostat wire. I found the instructions posted here of tremendous value in confirming that I could update the thermostat to an ecobee3 lite using their five wire to four wire adapter that was included in the box. I was able to make all of the wiring connections, have the ecobee installed and the system up and running in less than 30 minutes. FYI, the Lenox internal wiring to the thermostat that I found is:

The BCC (blower control) is a printed circuit board. This board operates the blower and monitors primary limit and gas valve functions. The control has a non-adjustable, factory preset for fan timing. Fan-off timings are adjustable. the board has two sections, 120 and 24 VAC.

Blower Speed Taps. Notice the speed taps at the upper right corner of the BCC board. Make blower speed tap changes here. Secure unused speed taps to the dummy "D" terminals. Connect the active heating tap to Terminal H. Connect the active cooling tap to Terminal A.

To Change a Speed Tap, turn off power. Remove the existing speed tap from Terminal H. Place the tap on a "D" terminal. Select a new speed wire. Place it on Terminal H. Restore power. Blower speed tap information appears on the G20 unit wiring diagram.

Adjust Fan-Off Timing by changing the position of a jumper across terminal pins. Fan-off timing is the interval during which the fan is inactive. The choices are in seconds: 90, 150, 210 or 270. (The fan-on time is non-adjustable. The factory setting for fan-on timing is 45 seconds.)Thermostat Terminal Strips on early model BCC boards are removable. Late-model boards (such as Type 65K29 in our ad) have permanent thermostat strips.

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Combiner box

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Lighting panelboard

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Elevator control panelboard

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Busway

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Grounded relay

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UPS

The MGE Galaxy 3500 from APC Schneider Electric features factory-installed hot swappable batteries and electronics to reduce installation time. The device features a TUV-certified 94% efficiency rate and ships with dual mains input and a built-in maintenance bypass switch. Additionally, the product includes an environment monitoring card, along with a start-up service to ensure proper configuration. The UPS relies on IP 51 reliability protection, a standard 2-mm thick steel plate enclosure, and user-replaceable air filters. www.apc.com #6

UPS

The Eaton 9395 UPS with Energy Saver System delivers 99% efficiency when utility power is within normal tolerances, and when the utility power falls outside acceptable limits for IT equipment, the UPS switches to double-conversion mode. The intelligent power core continuously monitors incoming power conditions and balances the need for efficiency with the need for premium protection. The UPS is rated for 550 kVA and provides N + 1 redundancy. www.eaton.com #7

Generator set

The Kohler Large Industrial Gas (180-400 kW), EPA-certified generators from Kohler Co. provide one-source responsibility for the generating system and accessories. The generator set and its components are prototype-tested, factory-built, and production-tested. The 60 Hz generator set offers a UL 2200 listing and accepts rated load in one step. The set meets NFPA 110, Level 1 requirements and conforms to the New Source Performance Standard for stationary spark-ignited emissions. www.kohlerpower.com #8

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