Honeywell circuit board wiring harness short Bryant furnace

[Tony Discenza]

Our oil fired furnace didn't kick on the other day when the temp dropped. T his happens once or twice a month during the winter. I simply access the r eset button and all is well (why the reset button trips occasionally is ano ther question). In this case however, the reset button had not tripped, no r had the breaker from the main power supply.

Until purchasing my own country home a few years ago, I lived in a large ci ty and always rented. I have almost zero mechanical skills. Now that I've retired and my income pared by 66%, I need to learn to do many a repair th at until now fell to others.

In the case of the furnace not firing, I called the local HVAC repair peopl e. The technician was puzzled. As he fiddled around with the main switch a ffixed to the side of the furnace, the unit fired. He assumed there was a short in that switch and after cutting power to the unit, proceeded to swap out the switch with a new one. When power was restored, the unit continued not to fire when called upon to do so. He then removed a cover panel that exposed a circuit board (Honeywell ST9103A). He poked at a wiring harness that is connected to the board (harness attached in upper right of board in photo linked below) and by wiggling same, the unit fired. Jiggling the ha rness resulted in the unit kicking on and off, on and off, in "fits and sta rts" as if there were a faulty connection somewhere. He positioned the har ness in such a way as to ensure the unit would fire (at least at that time) , replaced the cover panel, and wrote me a bill for $164. The bill read "f ound there to be a loose connection on wiring harness, corrected problem, u nit running well."

While I can't argue with his assessment of the situation, I've learned to p oke around a little myself next time before making a phone call that I know will result in a minimum $85 just for the call.

With that said, this morning the unit failed once again to fire. I accesse d the panel myself and by wiggling the wiring harness, all systems are agai n GO. What is the long-term fix here? Do I attempt to replace the board ( $80 for a replacement)? Do I purchase a new wiring harness and replace tha t? Both? Is either job very complicated? Thanks in advance for any assis tance.

[KLayton888]

Sounds like you've got bad solder joints on the connector pins on the circuit board. Shut the power off, remove the board, resolder the connector pins on the board and it should be good to go.

[trader4]

Certainly could be that. Could be corrosion on the connector, pins, etc. too. You have to wonder about the service tech that charges $164 and relies on "postioning the harness" to keep it working.

[Tony Discenza]

board and it should be good to go. >

Sounds like something within my abilities. I just might give it a go, thank s.

Any tips on how to clean the pins and connector? Pipe cleaner? Something a bit more abrasive?

"postioning the harness" to keep it working. >

Especially knowing that eventually (probably due to the vibration that occu rs each time the unit fires) the problem will reoccur, which in fact did ha ppen today. They get $85 for the call and $90 per hour one on the job. Ho w should I have handled this? He was in fact at the house for 45 minutes? Should I have objected to the hourly rate because the fix was so simple? H e did offer to replace the board (or at least dig deeper) at additional exp ense to me for his time. At that point I showed him the door, knowing that I might be able to address this myself, at 100% less in labor.

Thanks again folks.

[trader4]

e board and it should be good to go. >

a bit more abrasive?

First I'd just inspect it. If the connector looks clean with no sign of corrosion, oxidation, etc, then I probably wouldn't do anything. Any auto parts store should have electrical contact spray cleaner.

I'd look for evidence of a cold solder joint near the connector. Those things can go for years, until finally they start to exhibit intermittent behavior. In fact, if you can't find anything else, I would just reflow the solder points near the connector, assuming it's possible with whatever board design that is. Make sure you use solder made for electronics,.

on "postioning the harness" to keep it working. >

curs each time the unit fires) the problem will reoccur, which in fact did happen today. They get $85 for the call and $90 per hour one on the job. How should I have handled this? He was in fact at the house for 45 minutes ? Should I have objected to the hourly rate because the fix was so simple? He did offer to replace the board (or at least dig deeper) at additional e xpense to me for his time. At that point I showed him the door, knowing th at I might be able to address this myself, at 100% less in labor.

If that's the rate and he spent about that much time, not much you can do. With some basic debuggins skills, you can fix a lot of things like this yourself. Also, it can be more effective, because you can catch it when it's not working. If it's intermittent and works when the service guy is there, it can just be a waste of a service call.

You would hope that he would have used a VOM while wiggling the various connector pins to see if there was a bad connection on the board. If it's repeatable, ie hold the cable this way and it works, hold it the other way it doesn't, it should be possible to find the root cause.

[Nightcrawler®]

You got robbed. The problem was not corrected and a more verbose description of said problem should have been given and a note should have been added that the unit was functional, but not repaired.

First, I would try to isolate the problem. Try and manipulate the connector without disturbing the wiring.

If nothing happens, try and manipulate each individual wire with a pair of needle nose pliers; moving left to right, up/down, and in and out. Do this at the connector first, and not knowing if there are two connectors, then the second connector or the solder points on the board.

So, I guess I should ask. Are there two connectors?

[Tony Discenza]

No, just one. I edited the photo below to identify the wiring harness in qu estion.

With respect to your view of the way I was treated on the service call (got robbed), it took the guy 45 minutes to identify the problem. Once identifi ed, he did offer to continue working in an effort to correct the problem (h e made a couple of off the cuff suggestions as to what he would do ... clea ning the connections, looking into replacing the harness if cleaning didn't work. At that point, at $90 per hour, I decided to take the ball into my own hands and run with it. So, while I wasn't happy with amount of the bil l, I didn't think I had a leg to stand on had I attempted to haggle. I sup pose I could've beefed about paying for his time to swap out a switch that was fine to begin with (15 minutes of the 45 minutes he was on the job) but other than that, I understand that he's gotta get paid for his time by his company. He made a point to tell me he didn't charge me for the new switch and he also did a smoke test on the way out the door, showing me a clean t est paper indicating a unit running clean.

Thanks for your reply. I'll attack the problem in the manner you suggest (i solating the connector or the individual wire).

[David L. Martel]

Tony,

If you haven't soldered before and have little DIY experience, it's not easy to advise you to pursue technical solutions. Here's something easy you can do. Buy a can of electrical contact cleaner (Radio Shack, most hardware stores). Turn off the power to the furnace. Disconnect the offending plug. Spray the connector at the pc board and spray the plug connections. Now plug and unplug a bunch of times with some wiggling action. If you are lucky you will remove the corrosion that is causing yur problem. Now plug the plug in firmly. Restore power and hope for the best. If that doesn't work I'd recommend finding an honest competent repair guy.

Dave M.

[Nightcrawler®]

Another thing to do is, as suggested, disconnect all power, and remove the board from the chassis, and look at the back side of the board where the connector is. Look for burnt traces.

Usually these connectors (Molex) are of a bullet type of terminal inside the housing, where the board side as metal tubes that the plug side, which has split tubes, that slide over the metal tubes on the board side. The clamping strength of the connector side will weaken over time and sometimes you just need to get a small, metal object (ice pick) into the Molex and gently pry them closer together so that they may make better contact. Of course, follow David's instructions, also.

[Tony Hwang]

Hmm, When I replaced a board on my old z Carrier furnace a pig tail cable extender was inclded with the replacement boards. It had M connector at one end and F at the other. Just to make the harness longer.