21 replies to this topic

[delawaredrew]

Long story but here's the background: I have a York gy8s080b16dh11b furnace that is driving me crazy. For the last couple years it has blown the 3a fuse on the board several times when we first turn the heat on before deciding to work normally for the remainder of the winter. Weird but as long as it was heating I was not going to spend too much time on it other than to swap the fuse out a few times until it decided to work. I work on home appliances so I know I shouldn't have ignored it this long but who wants to go home and crawl under their own house?

This fall it blew a bunch of fuses, more than previously. I finally was at the thermostat when it happened and saw that the heat anticipator glowed and sparked before the fuse blew. It was a heat pump style thermostat, unnecessary for the gas furnace we have so I swapped it for a programmable Honeywell and all was good. I did find a few nicks on the wires behind the thermo so I pulled some slack up and cut them off just as a precaution.

2 days ago it began blowing fuses again, sometimes it would run for a little before blowing the fuse but never more than a few hours. Thinking that the fuse was on the dc circuit going up to the thermo I inspected that wiring and there were rubs through the wire sheath and nicks all over where someone had stapled it along the beams. So I replaced the whole run from thermo down to furnace. No change..

It powers up normally, with a heartbeat green flash until the thermo calls for heat, then the fuse blows instantly...
Recalling the last errors gives me a 3 flash, a 6 flash, a 3 flash, and then a 7 flash. I can account for these errors as it was pressure hose was clogged 2 yrs ago.


Anyone think there is anything to do other than buy a new board?

[jumptrout]

Something in your low voltage circuit is drawing too many amps.
I do not believe it is a board problem. The fuse is designed to blow before the problem affects the board.
Since you replaced the stat wire and still have the problem,you must check the individual 24 volt components.
Follow your wiring diagram.
It it blows immediately,the first component in series is the problem.
If there is a delay in blowing then the second,third component etc.

[delawaredrew]

Thanks for the info, I'll start looking.

[RegUS_PatOff]

It seems the only thing powered by the 24v is the Gas Valve.
(through the Thermostat, Safety Switches, and the Gas Valve Relay Contatcts)
A bad Gas Valve, drawing too much current, could overload the Thermostat Heat Anticipator and also blow the Fuse.

[Bobice]

High Efficiency Gas Furnace Tries to Start - Clogged PVC Pipe Condensate Drain

If you have ahigh efficient gas furnace(usually indicated by having 2 to 3 inch white plastic PVC pipe running from the furnace all the way up to the roof or through an outside wall from a crawl space) and it is real cold outside a common issue is having a frozen condensate drain.
In this case look outside your home for where the condensate drain is located, many times there is an ice build up around it and this blocks the water from draining properly. You can use a hair dryer or hot water and melt the ice from both outside and inside the pipe and the furnace should start working once the water drains out

[delawaredrew]

It seems the only thing powered by the 24v is the Gas Valve.
(through the Thermostat, Safety Switches, and the Gas Valve Relay Contatcts)
A bad Gas Valve, drawing too much current, could overload the Thermostat Heat Anticipator and also blow the Fuse.

I come to the same conclusion, only the safety and gas valves use 24v.
SO assuming I am understanding this correctly (a huge assumption, I know) the fuse blowing prior to any action in the furnace seems to indicate a wiring issue? If I get the ignition sequence right I'd get the usual fans prior to any power to the valve, so unless the valve was internally shorted, I likely have a problem in the wiring going through the safety system.
If it was a blown safety I'd just get no gas flow, but all the usual ignition process up to that point?

I'm still hoping it isn't a bad gas valve relay on the board, but after 3 yrs of intermittently doing this I would expect it to outright fail. I pulled the whole board off to look for obvious burns or burst caps or resistors and it looked ok.

Just FYI: Here's the manual I've been looking at.

Thanks for help on this, I have nearly exhausted my patience and it's great to have input that isn't mixed with my desire to grab a 2lb mallet and "fix" it once and for all!!!

[RegUS_PatOff]

looks like the same manual...
it could be a bad Gas Valve ..
maybe it's drawing nearly 3 amps... when it shouldn't be ...
Do you have an AC ammeter function on your multimeter ??

[delawaredrew]

RegUS - you posted while I was down below so I didn't check amp draw, I did the simple check though of unplugging the gas valve and it still blew the fuse immediately. That was just a quick check though as I don't really expect that the valve is the issue since it blows the fuse long before it should be energizing that valve. More info follows:

Update: For unknown reasons after screwing with it for several hours and not really finding a problem it is heating again...????WTF#$%???

I probed everywhere I could see a reason to look at and nothing was grounding out/shorted/obviously loose etc... the 24v system is only a few components.

I think maybe the transformer is the issue. I disconnected the thermostat so I could power the board up without blowing the fuse, applied 120v and kept briefly seeing 120v when I expected about 24v at the trans secondary. It was only momentarily then the voltage would go down to a more reasonable 27v. I use the same meter I use daily at work and have never noticed it being wildly off and wouldn't expect it to show that big a drift from spec even if it needed calibration. However I do not have much experience with AC transformers so maybe this is a red herring.

I did unplug and replug a lot of connections during testing, so maybe that alone "fixed" something, it happens at work sometimes and I won't argue with a working unit; but it is annoying to not fix anything but be successful. That is not satisfying at all. I like known broken things that I can fix or change.

I'll see what more cycles brings but fully expect it to fail again.

If anyone has any thoughts about that transformer measurement please enlighten me.

Thanks
Drew

Edited by delawaredrew, 30 January 2012 - 07:14 PM.

[RegUS_PatOff]

... unplugging the gas valve and it still blew the fuse immediately
... I think maybe the transformer is the issue.
... kept briefly seeing 120v when I expected about 24v at the trans secondary. It was only momentarily

1) then there must be a short in the wiring (or the terminals / bodies of the safety switches shorting to ground)
2) I don't think so ... the Fuse is in series with the Transformer secondary .. something wrong down-line
3) doesn't make sense ... but if so, still wouldn't blow the Fuse with the Gas Valve disconnected.

[delawaredrew]

1) then there must be a short in the wiring (or the terminals / bodies of the safety switches shorting to ground)
2) I don't think so ... the Fuse is in series with the Transformer secondary .. something wrong down-line
3) doesn't make sense ... but if so, still wouldn't blow the Fuse with the Gas Valve disconnected.

I don't know what to make of it all either, it has restarted successfully twice now though. So I know no more than I did before. It'll recur I am sure.

When it does I'll crawl back under and look again, if the trans thing is not an issue; than wiring or the safeties are all there is besides the board. If I am reading the schematics correctly the whole gas valve circuit including the safeties is not in play until the gas relay is energized. To complicate though that schematic isn't quite a match for what is under my house, close enough to give an idea but... I did find continuity to ground in a few places in the safety wiring that didn't feel right but it was getting dark, my flashlight was dying and suddenly it began working so who knows...?

Edited by delawaredrew, 30 January 2012 - 08:36 PM.

[RegUS_PatOff]

... If I am reading the schematics correctly the whole gas valve circuit including the safeties is not in play until the gas relay is energized.

... if any wiring from the "left" side of the trans secondary, up to and including the "left" contact of the Relay, is shorting to "ground",
that would short (that one side of the trans) to ground, (the other side of the trans secondary)

[Bullstok]

Don't forget checking any added accesories on the 24 volt side. Improperly added humidifiers, uv lights, or zone controls tied into the board (especially if blowing fuses) or tied directly into the transformer secondary can draw more VA than the transformer is rated for.

Edited by Bullstok, 31 January 2012 - 09:37 PM.

[jumptrout]

Is the neutral side of the LV transformer grounded to chassis? It must be.

[RegUS_PatOff]

Is the neutral side of the LV transformer grounded to chassis? It must be.

yes, as shown in diagram

[RegUS_PatOff]

... unplugging the gas valve and it still blew the fuse immediately.

here's a test (if you're up to it)

With the Gas Valve disconnected:
Using some small insulated alligator clips, make an "extention" cable connected to the empty Fuse Holder.
Length determined by the distance to the furthest Safety Switch.
Use wire ties to secure the cable somewhere to the Board or Furnace
so that any external movement of the cable won't disturb the alligator clips / connections.
Make sure they don't touch each other, or any other metal or circuitry.
At the other end of that cable, use a small 24v lamp, or (2) 12v automotive bulbs in series.
If and when there is a short, the Light Bulb will illuminate.
Watch the Light Bulb while you "jiggle" the wiring all the way to the Safety Switches...
and give each Safety Switch a slight "hit" with the handle of a screwdriver.

[telefunkenu47]

am i missing something here? where is the fuse on this schematic.??? couldnt you remove the fuse and read across it with your fluke 77 or similar meter?

[RegUS_PatOff]

... am i missing something here? where is the fuse on this schematic.???
... couldnt you remove the fuse and read across it with your fluke 77 or similar meter?

1) I don't see it on the schematic, either, but it's seems to be on the Controller Board
2) yes, but seems to sometimes blow the Fuse right away, even with the Gas Valve disconnected....
could be an intermittent short.. hence the Light Bulb test cord

[Shootist]

I had an A/C system that would pop the fuse once every few of months before I finally found the shorted control wires hidden under tape. Most A/C supply houses sell a little device called a "Mini-popper" that you plug into the little fuse connections and it has a little reset button. It'll keep you from going through a pocket full of fuses until you find the problem.

[delawaredrew]

I had an A/C system that would pop the fuse once every few of months before I finally found the shorted control wires hidden under tape. Most A/C supply houses sell a little device called a "Mini-popper" that you plug into the little fuse connections and it has a little reset button. It'll keep you from going through a pocket full of fuses until you find the problem.

Yeah I've been thinking of something like this, I have a 15a resettable fuse from my days of working on MWs but I haven't sought out a 3a version.

The system has been working fine since the last time I posted, much the same as other times it has had issues. If I can find the motivation over the weekend I may go under and check out normal ops, I've been avoiding that since opening the panels allows it to suck dust in from under the house, and it's a really fine dust.

If I had to guess I would think there is a short to ground or a bad limit in the safety system as I saw continuity to the cabinet at a few spots I didn't expect, and as before "fixing" it seemed to happen after I moved wires around and plugged/replugged various terminals. I may be able to determine more when it is running properly; though the safeties on the burner are not fun to get to if it is burning. Mostly I want to see when it powers the safety circuit. The diagram shows wiring in series leading to gas valve similar to a dryer, on this one the safeties' wiring returns to the board, probably for the troubleshooting capacity of the board.

Thanks to all who have posted/helped on this... I am sure I will be back.
Drew

Edited by delawaredrew, 03 February 2012 - 09:45 PM.

[RegUS_PatOff]

the Safetys, Gas Valve and Relay contacts are all in series ..
none of that wiring is monitored by the Board for troubleshooting ..
You could do the Fuse / extension test with the Furnace not running and the Gas Valve disconnected