How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask BillyHvac Your Own Question
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22627
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Type Your HVAC Question Here...
BillyHvac is online now
A new question is answered every 9 seconds

I have a Lennox Elite Series furnace, GHR2603-75-2. It was

This answer was rated:

I have a Lennox Elite Series furnace, GHR2603-75-2. It was installed in 1998. The furnace would not turn on and I discovered that the furnace house breaker was off. I found out the control board went bad (Black scorch marks). So I ordered a new one 21D83M-843 White Rodgers to replace the 50A62-120 Lennox Surelight board that was in there.

Well after hooking everything up to the new board, I'm getting zero power to the Cool, Heat, Fan, EAC, XFMR and Line terminals. The only one showing 120 Volts is the HUM terminal.

How I hooked up the wires to the new board:
ACB Cool (Old Board) to Cool(New Board)
ACB Heat (Old Board) to Heat(New Board)
ACB Low (Old Board) to Fan(New Board)
120 Vac Hot (Old Board) to Line (New Board)
120 Vac TX (Old Board) to XFMR (New Board)
3 White neutral wires to Neutral 120 VAC on new board.

The transformer has four wires: Yellow, Black, Blue, and White. Heres how its wired:

Blue wire to 3 amp circuit breaker. 3 Amp circuit breaker to blue wire on the wire adapator that came with the new board.

Yellow wire to the yellow wire on the wire adapter that came with the new board.

Black wire to XFMR.

How the Door interlock switch is wired:
Black wire from switch to Burner exhaust fan.
Black wire from switch to Line.

I was thinking something is wrong with the way the switch is wired with the new board. It was wired like this before. Only difference being that on the old board the terminal was labeled 120 VAC hot.

Heres the manual for the new board

Mabye someone here can give me some insight, or tell me what I'm doing wrong.

My name is Billy,

Give me a few moments to look over the diagrams and I will be back soon.



first thing....did you use the 4-6 pin connector and the 9-12 pin plug?

Customer: replied 3 years ago.

Yes I did.



Customer: replied 3 years ago.

Yes I did

Thank you,

Now just to have a black wire from the door safety switch...and this is on "Line"

Customer: replied 3 years ago.

That is correct.

Thank you.

When the black wire is on Line...and the XFMR is not hooked up you read 120v on the terminal XFMR? The black wire goes to the transformer?

Customer: replied 3 years ago.

No no voltage at XFMR.


Yes the black wire goes from XFMR to the transformer.

Thank you,

You have a bad board.

I apologize for that type of news. But you are chasing a no fix situation.

Whenever 120v is applied to LINE...XFMR is automatically hot to feed the transformer.

I am afraid you simply have a board bad out of the box. It happens more than I like to say.


Customer: replied 3 years ago.

Id like to add that when I connect the black transformer wire to HUM instead, the board does power on.


How should the door switch be wired, I know one wire to line. But the other wire was going to the exhaust blower. Does that make sense?-

There should be a hot coming from the power switch into one side of the door switch...and then out of the door switch a hot to LINE terminal

Customer: replied 3 years ago.

Ok, I think I may just have to add a wire to the switch tthat hooks to power. Maybe its different then the way the old one hooked up.


The black line thats currently connected from door switch to the exhaust fan, where do I plug that into on the board so it comes on when the heat comes on.

The wire to the exhaust motor should done from one of the plug connectors on the board.

Dont you have a black and white from the inducer to a plug on circuit board?

Customer: replied 3 years ago.

Yes, the black was plugged into the door switch and the white is connected to 120 VAC neutral.


I'm thinking the installers did something funny during the install back in 98 thats causing me problems now.


I think running a live wire to the switch, and hooking up theblack wire from the exhaust blower to a pin on the board might solve the problem. I'm thining the EAC pin? Which used to be ACC on the old board

It has to be the specific connection on the board.

It would not have ran with the inducer hooked direct..the exhaust would have run nonstop.

Wecannot use the eac as it is only hot when the blower engages (eac= electronic air cleaner) You have a plug on the board with 2 blacks and 2 whites correct?

Customer: replied 3 years ago.

You mean the 6-pin to 4-pin? Yes I do. That hooks up directly to the main power coming in.

It is a plug on both ends..4 to 6. If power is hooked to that...then how is Black power wire from door safety switch hooked to LINE terminal?

Customer: replied 3 years ago.

The 6 to 4 adapter plugs right into the board, that adapter plugs right into the house power supply.


I'm just going by what the manual says where to hook the switch to. It was on 120 VAC HOT on the old board, but the diagram in the manual says that 120 VAC HOT is now LINE on the new board.


From what I can tell, the switch does not have power, thats why the board is not powering on. After powering the switch, it should turn on I would think. Now to figure out where the black line from the exhaust blower plugs in.


see page 2 here

The 4 terminal plug feeds exhaust and ignitor.
The power goes to a plain terminal marked LINE
Customer: replied 3 years ago.


Thats an image of the board thats labeled. Where would the black wire coming from the exhaust fan plug in?. This is a hot line, put 120 through the line and the blower powered on.

The exhaust fan has a set of wires that go to a plug. Then this set comes down and plugs onto board where the 4 pin is. The black and white from exhaust and the black and white from the ignitor plug into the 4 pin position.

The hot black wire from the door switch does not go to a goes to a terminal LINE
BillyHvac and other HVAC Specialists are ready to help you
Customer: replied 3 years ago.

This hot black wire is supposed to be plugged into a terminal somewhere. It was before. It powers on the fan. There is no way to connect it to the 4 pin plug unless I would splice it in.

Your black and white coming from exhaust is not in a plug?
Customer: replied 3 years ago.

It is a plug.


But, the male end thats plugged into the plug coming from the exhaust is just two wires, one white, and one black. Both wires have normal connectors on the end to hook them up to a terminal.

Customer: replied 3 years ago.

I have to head off to work, Ill deal with this tomorrow. I'm sure it just something simple thats being missed.

Just check in tomorrow..keep this on your end until then,,I will continue to look at the wiring
Customer: replied 3 years ago.

OK just wanted to let you know I've solved the problem. I had the plug that was going to the exhaust blower mixed up with the plug that goes to the main house power. They are the same. It was wired correctly on the board and door switch, just plugged into the wrong plugs. Stupid mistakeCool


Thanks for your last answer, it got me thinking about it and discovered the problem.