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White Rogers Integrated Control Board

Malcolm_33
Malcolm_33 Member Posts: 9
I'm trying to help out my neighbors; they're elderly and on a fixed income. I have handyman experience with HVAC but am not schooled. Their Trane furnace doesn't heat, although the AC works. I've already changed out the control board, a 50A65-5165. After I changed the board out, the inducer fan came on, the pressure switch circuit closed, and that was it. It did not time out; the inducer would keep running but the ignitor would not glow. I put my testers on it and it was getting approximately 68 volts (it's an 80 VAC ignitor, and the board instructions say it has to be a White Rogers because the board senses the lowest temperature at which it will ignite gas. I replaced the ignitor, and got the same results; it would not glow. I checkd for continuity through all the limit and roll-out switches. I thought maybe some wires were misplaced on the board so I pulled the spade terminal wires and made sure they were on the proper (marked spades), and now I'm blowing the 24V 5Amp fuse whenever I call for heat. The AC still works. I'm mystified - I think somehow the board has decided 68 volts is enough for the ignitor but it isn't, but I don't know why all of a sudden I'm blowing that fuse (immediately) when I call for heat. Any geniuses out there?

Comments

  • DZoro
    DZoro Member Posts: 1,048
    What was it doing before you changed the board?
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    Nothing. No diagnostic light, nothing. And it was getting 110volts. Btw, now the diagnostic light flashes "Normal- no call for heat" until I call for heat, and then it goes out and does not flash any codes.
  • mattmia2
    mattmia2 Member Posts: 7,217
    Check the wiring against the schematic. You almost certainly hooked something up wrong to the control board
  • mattmia2
    mattmia2 Member Posts: 7,217
    Once you figure out the fuse blowing (which is either a wrong connection or something touching that shouldn't be, possibly a chaffed or melted wire but more likely a connector or part of the tstat wiring) check the resistance of the ignitor from the board connection and of the wiring but with it unplugged from the board.

    I think that is a sure light system and you should be able to find a description of the algorithm somewhere. It only sends the power required to light the gas to the ignitor to greatly extend the life of the ignitor. I think it basically increases the power until it detects a pilot flame then remembers that setting for next time. I think but am not positive it gets reset when power is cycled.
    Malcolm_33
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    I did that (checked the wiring against the schematic).The only wires I pulled and replaced were the hot and neutral Lines, the hot and neutral to the transformer, and the neutral to the blower motor. All the low voltage wiring is attached to the board through a 12-pin connector, that you can't put on wrong. And my short is definitely in the low voltage - if I disconnect either of the low voltage wires coming out of the transformer, the fuse doesn't blow. It also doesn't blow if the thermostat isn't calling for heat. I thought maybe the gas valve was bad but I don't think the voltage gets there until the inducer starts up, the ignitor heats up, etc.
  • mattmia2
    mattmia2 Member Posts: 7,217
    edited December 2019
    It is remotely possible but unlikely that any of the components would fail as a dead short. It is very likely that in moving things around you caused someone else's poor workmanship to short out. Does the fuse blow immediately or does it start some of the cycle like running the inducer fan first? If it does nothing then look at the tstat wiring, if it does some things, look at the wiring to the step in the process where it blows

    An ammeter on the 10 or 20a range between one of the xfmr terminals and the control board (in series) will tell you if it is an overload from something like a cooked coil that is blowing it or if it is a short.

    I think that has 2 (or more if it has multi stage heat) has valves, one for the intermitant pilot burner and one or more for the main burner.

    Make sure the tstat wires match the letters at the tstat and the control board, the colors dont necessarily follow the letters, did you check before you disconnected it?(if you did, I think you said they go to a pluggable connector)
    Malcolm_33
  • JUGHNE
    JUGHNE Member Posts: 10,333
    It is possible that the stat cable is internally shorted.....say the W is shorted to the C and tstat closes and you short the R thru stat to W which is shorted to C.

    I would disconnect all the tstat from the furnace and then jumper R to W on the board....this is what the tstat actually does.

    When ever I disconnect tstat cable from any board, providing there is extra cable, I cut the colors leaving an inch on the board terminals. Isolated from each other of course. This is then a record where things were laid down....sometimes mislaid.

    If furnace then works I would disconnect the tstat end and check for shorts between wires within the cable. Then you can wirenut them all together at stat and check for continuity on all conductors and also shorts to ground at the furnace.
    It is simpler than it sounds. It takes the stat cable and wiring out of the equation.
    Have done this on someone's bad install and found the problem.
    mattmia2Malcolm_33
  • mattmia2
    mattmia2 Member Posts: 7,217
    BTW, the last brute force method to troubleshoot this is to unplug everything from the control board and hook up one thing at a time in the sequence of operations and see which one it blows the fuse on (the first thing being a temporary jumper between r and w so it powers on with a heat call each time)
    Malcolm_33
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    Thanks to everyone trying to help! I'll take all your suggestions and let you know what works.
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    As far as the low-voltage dead short, I took the thermostat out of the equation by disconnecting all the thermostat wires from the board and then jumping the white and red, and it's still shorting out. I took the limit switch/s wire off the first limit switch and it didn't short. I plan to put that one back on and take the second in the series off, etc, in sequence, and see if it shorts, but I think that is just a single sequence without a neutral or without a hot and I won't find the short in there. So, it would help to know what is the initial low-voltage component. Btw, I did get a diagnostic read from the board of an open limit switch when I took the limit switch sequence off.
  • JUGHNE
    JUGHNE Member Posts: 10,333
    Possibly your limit circuit has a short to ground.
    I would ohm that circuit out to ground.
    There may be 2 limits on the fan blower housing, one on the inducer blower housing, 1 or 2 rollout switches, one somewhere on the air plenum.....just follow the wires around.....they are usually all in series. One opens shuts down fire. If circuit grounded might be blowing fuse with a call for heat.
    Malcolm_33
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    Jughne, you were right. I followed the limit circuit, and the high limit was shorted to ground. I just wired around it and ordered a new one. That solved the dead short, and now the ignitor glows, the inducer does its thing, and the gas valve get 24volts for about four seconds - I can actually hear the gas start to flow, and then the system shuts down. I'm reading the manual and may be able to figure this out on my own (bad flame sensor?) but I'm still open to any and all advice! Thanks everyone for your interest.
  • mattmia2
    mattmia2 Member Posts: 7,217
    DO NOT RUN IT WITHOUT FUNCTIONING LIMIT CONTROLS.

    If you can't find something that is bent or chaffed or melted and shorted, you will have to wait until you get a new part to run it. (although you can cautiously troubleshoot the original problem if you are careful to make sure it isn't overheating while you are troubleshooting)

    Does the gas light before ti shuts down? What error does it have at that point?
  • mattmia2
    mattmia2 Member Posts: 7,217
    Cleaning the flame sense probe with something like scotchbrite might get it working again. Oxide on the surface will insulate it and prevent it from properly detecting flame. It uses flame rectification to prove flame so a current must flow from the probe, through the flame, and back through the burner to the ground of the control board.

    This is the manual but I think you have already found it:
    https://climate.emerson.com/documents/50a65-5165-instructions-en-us-3583534.pdf
    Malcolm_33
  • DZoro
    DZoro Member Posts: 1,048
    What was the symptoms before the board change out?
    Was the old board a 50A65-5165?
    Very unusual to have so many problems, usually there is only one fault not 2,3 or more.
    D
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    I live across the street from these folks, and a couple months ago an electrical surge blew the power supply in my computer (it actually woke me up; I heard it buzzing and then there was a huge SNAP! and the computer died), and three plug-in surge suppressors literally melted - you could see the plastic disfigured over whatever overheated. And, two of those were in series! I suspect the same surge blew up the control board on their furnace and a few other components besides. Think that's why this whole thing has been driving me nuts. I had already bought one control board for their furnace a year and a half ago or so, so I kinda slow-walked buying another one, until she told me she was using an electric heater that she was afraid of and was getting up a couple times a night to check on it.
    The old board was a 50A65-475; I must have gotten the model number for this new one from the model number of the furnace, or it was the recommended replacement. Can't remember, I've been working on this for a week off and on and I bought it online.

    I don't get an error code when it shuts down; it just shows the rapid-flash "heat called for, operating normally" throughout. I'm thinking the burners themselves might be so dirty the gas doesn't get through properly, or there might be another gas shut-off that isn't next to the furnace (the gas stove works). I'll loosen the flex line and see about that. The gas valve gets 24V for maybe 4-5 seconds but the gas doesn't come on right away, and when it does (you can hear it - at least I assume that's what I'm hearing), it shuts down immediately. Btw, it does attempt another cycle after one minute.
    Sorry to be so verbose; hope this site doesn't have a yearly word limit.

  • JUGHNE
    JUGHNE Member Posts: 10,333
    Which limit was bad/shorted?
    Did you jumper only that one?
    Does this have a pilot or light the entire burner to start?
    I would go for flame sensor cleaning, of course if it never lights the gas then no flame to sense.
    Pilot burner, if there could be plugged.

    If you get it going and have a limit jumpered out you should not leave it unattended......but which limit button was it?
    mattmia2
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    It was the high-temp limit (I think that's what it's called) - it's a 190 degree limit. I only jumpered around that one.
    I never do get a flame - the gas valve takes like four seconds to open, it seems (monitoring the voltage going to it), and as soon as it opens, everything shuts down. Maybe it's a two-stage gas valve, but I don't understand how those work.
    I just want to get it working and then I won't leave it on until I put on a new limit switch.
    No pilot light. Just the ignitor.

  • JUGHNE
    JUGHNE Member Posts: 10,333
    Was that limit switch physically located in the air flow of the plenum? That is the serious one.
    There may be a small electric switch on the gas valve....easy to move unknowingly. And of course the gas supply valve is on....

    I am not familiar with Trane, but have had high limits fail from cycling on lack of air flow.....air filters.......small duct work.

    Most gas furnaces I have seen will do a post purge immediately with the inducer fan and try to relight maybe 3 times and then lockout.
    Malcolm_33
  • mattmia2
    mattmia2 Member Posts: 7,217
    if that is the right number at the top, according to the theory of operation it just opens the main valve, no pilot valve.

    It will retry lighting i think 10 times according to the instructions before locking out.

    the gas valve could be a slow opening version, finding the data sheet for that valve would tell you, seems kinda likely since it is direct ignition instead of intermittent pilot

    the type of damage you describe usually happens from a neutral getting broken.
    Malcolm_33
  • Malcolm_33
    Malcolm_33 Member Posts: 9
    To follow up, I fixed the low-voltage short which was in the limit circuit, and in the high-limit switch in the plenum, by removing it and putting it back in. It had a metal plate under the sensor which either protects it from the flames or gives it its reading of the temperature, or both, and evidently they were touching. Maybe a loose bottom screw, which held both, but anyway, I took it out and put it back and now it doesn't short and gives continuity through the terminals. The gas valve is getting 24V at the proper time in the ignition cycle and isn't coming on, so I've ordered an identical replacement. I'm hoping I can find a circuit surge protector so I don't have to go through all this next year or the year after. We live in East Atlanta and are supposedly on the oldest electrical grid in Atlanta. Power goes out here a lot.
    Thanks to everyone for your help. I really was the point of just throwing in the towel until I started getting some ideas in here.