Any hvac techs out there? Just replaced a control board and it's not working. Main fan doesnt come on. I've probably screwed something up but I cant find it. It's a york unit, single stage using a universal board white Rodgers 50m56u-843.
Fan relay comes on when I jumper thermostat connections. Heat goes through the motion but gas never opens.
Gonna drop 30 degrees overnight and I've been at this 5 hours. Shouldve been an hour tops

Have you installed the jumper for the york models?

Also make sure your gas valve has the correct contact rating.

Also what was your previous control board? The wiring harness connector might be slightly different on the wire connections.

Also if you haven't had someone look over your work that is always worth it. Peer reviews can catch so many mistakes, you may think it's perfect and then BOOM they find something obvious. I built and wired industrial HVACS for hospitals and other large businesses for a year, Motor control centers for two years, and now I assemble semi conductors for a leading manufacturer.

It's a replacement for a source 1 1012-03-9651b. No I didnt install the jumper. Model number didnt match.....and in the span of a few hours I've misplaced the damn jumper.

Try to verify the wiring the best you can get a ladder diagram of the old control board and the new and compare the main harness. Also there should be two jumpers the one that goes on the 12 pin board and the R/O jumper pin.

There is no mention of the jumper on the 12 pin connector. There is on the old version of this board. The R/O jumper I'm not sure about. Do you know specifics of it?
If I'm correct it looks like one of the pins on the 12 pin doesn't match the old board. It's supposed to be plug and play. None of the included adapter harnesses would work because this one plugs in directly. The 4 pin matches up well. Inducer fan motor and glow starter work fine. If I jumper G and W I get a relay click but no fan. Fan was working just fine before this board install. I'll have a meter with me in the morning and I can check the output of the heat and cool terminals and anything else that may need checking.

I have nothing to offer except my appreciation for this community coming to help out. I know nothing about home HVAC, but it's cool to see someone else's capabilities shine for another member. Props!

Without being there to see it I don't want to make to many guesses. If you can hold out till morning it's already kind of late so may be the best option, wait until you get the multi meter. Get the Ladder diagram for both old and new board, verify the connections are the same, then check voltages throughout the system, make sure everything is getting the correct amount of volts/amps, trigger the relays see if the power is reaching the fan. Also read up on the gas valve and verifying the contacts on that. It's basically a trouble shooting game at this point. Ladder diagrams are amazing at this because you can just trace and highlight everything that you have already checked/works.

Sjd6795 said:

Have you installed the jumper for the york models?

Also make sure your gas valve has the correct contact rating.

Also what was your previous control board? The wiring harness connector might be slightly different on the wire connections.

Click to expand...

I installed the jumper and it fired up.
Now it consistently runs for a little while and then flags a high limit error and shuts off. It cycles again and fires up again after it cools. I highly doubt limit is bad.
Makes no sense. Also get a weak flame sensor error for the first 10 or so sec of flame startup. I assure you it's not weak. This is such a simple thing I'm just at a loss.
I kind of wish I had the original style board instead of this different replacement. This all started when the original board flagged a pressure switch code. I put a new pressure switch in and it ran for a day then flagged again. Cleaned out the orifice where the tube goes. Ran intermittently but never correctly. Kept flashing pressure switch code. I chased it and chased it. Finally realized it I pushed on the board slightly something made connection and it fired up. The very moment I let go it shut off. I was able to repeat this many times. I assess this as a bad board and this is where I'm at now.

this board is listed a direct part number replacement for what I had. I checked it number for number. I also installed the included hot wire ignitor included with the board.

So other then the high limit error no other codes? You have indicator lights I assume if so what color flashes and how many times? The fan is coming out now?

yeah everything is workign it just flags a high limit error and shuts off. After the main fan runs it's cool down it fires up and starts over again. I suspect after so many high limit errors it's going to shut down completely. I'm hoping I don't have a cracked heat exchanger or something more serious.

You said you replaced the pressure switch so that should be fine sometimes they get stuck in open or closed. You did say it kept throwing a code about it so maybe the pressure switch hose can also be bad. Are all of your fuses good?

Any restrictions in air flow, clean filter, blower motor working? Did you find the R/O jumper(I doubt this is your issues though). Check the flame sensor rod if you are getting a weak flame it could be faulty cleaning gently and even checking it's position to be correct.

It sounds like overheating for sure if the new board was listed for a direct replacement and you checked the wiring to make sure everything matches up, it almost has to be hardware at that point. Check the thermostat as well.

I would try testing the high limit switch if you have an ohmmeter depending on your model it will also control fans does the blower motor turn on at all?

The high limit will only be a problem if you adjusted the gas pressure and/or the fan speed has been changed. My guess is your fan speed has been changed. If you have a temp sensor like the ones used for cooking you can put it in the ductwork directly above the unit. You should see a temp of 100-120. If you get to much more than that it will cut out on high limit. Do not adjust the gas if you have not already!

Sjd6795 said:

You said you replaced the pressure switch so that should be fine sometimes they get stuck in open or closed. You did say it kept throwing a code about it so maybe the pressure switch hose can also be bad. Are all of your fuses good?

Any restrictions in air flow, clean filter, blower motor working? Did you find the R/O jumper(I doubt this is your issues though). Check the flame sensor rod if you are getting a weak flame it could be faulty cleaning gently and even checking it's position to be correct.

It sounds like overheating for sure if the new board was listed for a direct replacement and you checked the wiring to make sure everything matches up, it almost has to be hardware at that point. Check the thermostat as well.

I would try testing the high limit switch if you have an ohmmeter depending on your model it will also control fans does the blower motor turn on at all?

Click to expand...

I found the R/O jumper. It was necessary as before the unit would cycle but shutoff before gas was delivered.
I've changed nothing on the flame sensor, didn't even touch it.
Blower motor is now working since installing the r/o jumper. I'm double checking the wiring today, measuring temperature and checking the flue. Nothing changed from before. I did trim the ends of the hose just to make sure they had not been stretched out. There are no other cracks in the hose. It is fine.
I duplicated the wiring from before. Same colors on cool and heat. I took photos from before so it's easy to verify.
Per some suggestions I'll check the high limit sensor it self just to see if it's actually cutting off and as stated above check the temp to see if it's faulty or simply doing its job. If temp is high I will find the root cause of that and fix it. Odd part about all of this for me is I changed very few things.