Goodman furnace ----Circuit board???

Hello,
I had a Goodman GMH 95 1155DX installed 9/08, Pennsylvania, NG. Ran fine all last winter.
This fall it had worked fine but the temps were warmer, then in November it stopped.
Did all the switch checks, and NO lights on the board, thought it was the board so I got in a new board and everything was fine. But 10 days later the same thing happens, I had picked up another replacement board to have, and exchanged it in and it then worked fine. But only for about 8-10 days(temps were cooler,more cycles), at which time I still had the old board and decided to reinstall it, and it too worked great but only for 8-10 days. I have now done this 4 times and can almost do this with my eyes closed. The boards work fine but only for a little over a week. My question is what on earth is causing this, on all boards and not right away. I am trying to do this without the $ of a tech coming out.

 

It sounds like, everytime you disconnect the board & reconnect it, you're resetting a relay or something. I don't think it would matter if you changed the board or not.

 

The manual for your furnace is here:

http://www.acoverstock.com/installat...MH95-specs.pdf

The circuit diagram for your furnace is on page 13.

Read through and follow the description of how to recover the last five diagnostic codes and report what those are.


You need to remove to carefully observe and report the sequence of events that take place when the thermostat is turned up for heat. You may need to observe that several times until you appreciate the details of what is happening.

 

Inspect the incoming high voltage wire connections for loose or melted wires after you get the past 5 trouble codes.

 

Thanks for the replies, No wires looks melted or fried, and the fact that just a new board will get it up and running wouldn't if there was a problem,right?
Also on the board, neither of them allow me to retrieve and recall past codes by pushing that little button, when this happens, I've tried.
A relay seems to be a logical thought.

 

I take it there is a diagnostic light and button as illustrated on the diagram?

You did follow the directions in note #6 to get the diagnostic codes?

When you do that, is the light steady on, steady off or what?

 

When I push the button on either board, nothing happens.
Next time, yes I have a feeling this will keep happening, I am going to try to take off a wire or 2 at a time to see if I can isolate the issue. I hate to keep saying this but the fact that it happens after 8-9 days and to both boards has me stumped, maybe something past the board, but wouldn't it show up sooner?

 

Flame Rectification


Many mechanics will replace the ignition module, then think they've solved the problem because the ignition system begins to operate normally. In reality, what has often happened is that by reconnecting the wires to the module, they've changed the ground connection and improved the sensing signal. In many cases, they may have achieved the same results by simply disconnecting and reconnecting the wires on the ignition module they thought was faulty.

 

Houston204,
that sounds logical, what do I need to do further?

 

Remove and clean your ground connections. Verify that the board is getting a good ground and that incoming ground is connected properly. Measure line to ground for 120VAC. Inspect the wire harness for pins that may have been pushed back.

I've been behind another tech that replaced a board 3 days prior and found the culprit to be a faulty ground connection. (dirt between the circuit board mounting plate and the furnace chasis)

 

You need to carefully observe and report the sequence of operation you observe when the thermostat is turned up.

What should be happening is that the inducer motor turns on and spools up, the hot surface igniter glows white hot and the gas valve turns on.

How far does the furnace get?

 

Whenever the problem happens, the furnace just dies. Attempts to retrieve the past errors by having the power on but the thermostat disconected have failed to produce anything. No lockout or anything, just dead. So that is why I jumped to the conclusion of a bad board, but the 2 of them "fail" after 8-9 days and in the past I had just switched out boards and that got it running fine for a few days.
I will try what Houston204 said, I had read where a bad or faulty ground can cause problems.

 

You need to be specific.


I take it you have the thermostat turned up. Is there an indicator light or symbol that verifies that the thermostat is calling for heat?

Does the inducer motor turn on?


Do you have a multimeter that measures AC volts and do you understand how to use it?

 

When it stops it's dead. No lights on board, no inducer motor turns on, no hot surface ignitor glows, and can't jump R and W to bypass the thermostat, 24vac out of transformer and into board, all switches/sensors that are N.C. are N.C., all that are N.O. are N.O. Flame sensor clean. 118v in.
The baffling thing is that either a new board or an "old board"(have actually 3 boards now in the process) will get it running fine right away but only for 8-9 days and I have switched out boards 4+ times. And when I look to recall the error codes when it is running fine, of course nothing shows up. But when they die,they and everything are dead and nothing works or shows up.

 

Again, your comments are vague. and you aren't answering the questions posed.

If you can't do that, it's pointless to try to help you. Contact a furnace repair company for help.


I'll try ONE LAST TIME:


1: Is there a light or symbol on the thermostat that indicates it's turned on?

2. Do you have an AC multimeter and understand how to use it?


What is the AC voltage at the R and W terminals when this fault occurs?

 

I have a meter.
The thermostat works fine, an ohm meter was used to determine that. There is 118v in to the furnace, there is 24v out of the transformer. But when it dies, there is nothing at R/W.

My question is why would several boards work fine for several days then,I guess they stop, and by replacing the board gets the furnace working fine right away? And I have reinstalled(switched out and then switched back in the "faulty board") a couple of times, so they don't really die,they work again.
Wires look fine, connections seem tight.

 

As I said, each time you remove & replace a board, you are resetting something else. That something else is the problem.

 

If transformer power exists during the outage, then the blower door switch is okay.

If no power at R, it looks to me that on the upper rightside diagram, it looks like all the low voltage wire safety switches that come into play after W(which is normal) - BUT, it looks like 24v power first goes through one (or 2) rollout switch(es), before going to R. Very important if true, and if you are even losing power to R.

Check that out guys, and see if you (agree) think that the way the drawing shows, that the current path comes off the transformer, then takes a right turn into the aux. rollout switches RO1 and RO2, then heads back left to R. If true(if I am reading the drawing right), roll out switch trip would cause break in R that would shut down everything after the transformer. Maybe they do this this way so that furnace even shuts down EVERYTHING for fear of possible carbon monoxide when a rollout gets tripped.

The part that does not make sense though is it says these are manual reset swithes, and goldknox has not been resetting these.

goldknox,

test the volts to ground from each rollout switch terminal to ground (4 terminals to test if 2 switches, and 2 terminals to test if one switch. IF you have 24 volt power there and at the transformer, when you have an outage!, then it could be a pin connector or other connector issues past the last rollout switch at pin 11, or any other connector points that may be from the last terminal on last roll out switch, to the thermostat terminal strip that activates R. These pin-type jack connectors can lose connection. Disconnect and reinsert. Also, before reinsertion, look to see if each split pin connector looks about identical with each other. But simply unplugging and replugging in may score through oxidation.

....................................................

Hopefully you do not dismiss this post, as I spent an extra amount of time reviewing the drawing, and trying to come to the conclusion I did.

 

ecman51`
Thanks for taking what must have been a long time to look over the wiring diagram.
As you correctly state, I have not been resetting the manual reset switches, I will try your suggestions the next time this happens.

 

Yes, as Ecman suggests, this problem has been acting like a bad electrical connection of some kind. A bad electrical connection often manifests itself as erratic operation of a circuit, which pretty much describes the symptoms here.

And since there is apparently voltage at the output of the transformer, but not at the R terminal, it's a matter of carefully investigating the intermediate parts, wires and connections to identify where the voltage stops when this defect manifests itself.

 

To help you understand the drawing better - in case you do not know - once power is supplied to R, it has to go thru the thermostat and comes back to the terminal strip with 24 volt power at W when there is a call for heat. [Do not be confused looking at the drawing when you see the line bridging R,W,Y,G, & C, because this 'line' is simply part of the rectangle of the drawing border around the terminal strip, not a pathway for voltage.].

With all this in mind, you can better track what is happening with the current flow both before R and even after W. When the stat is turned down(no call for heat), anything downstream of terminal W (all the safety stuff located higher up in that upper right quadrant of the drawing)is shut off. But anything upstream before R(stuff lower in the drawing, heading towards the blower door switch and incoming line voltage, would still have 24 volt power, regardless of if the stat is calling for heat or not.

The pin numbers I refer to can be seen and individually followed in the upper center drawing on the left. Upon careful review you will see the left and right drawings actually show the same parts. The drawing on the left though actually identifies the different color wires involved with each device. Find that pin jack connector with numbers 1 -12(has 3 vertical rows of 4 pins). Pull that jack apart and reinsert and pay attention if any signs of moisture around it from say leaking AC condensate from above (if you have central AC). Or, wait til you have failure! and jiggle it or any connection that is after the transformer, but before R. Your problem would not even have anything to do with relay pins 1 & 2(located on the board below the 12-pin connector), which change 24 volt power to 120 volt power for the inducer, because that comes after terminal strip connector R. And so does the pressure switch. And since you say you even lose power to R, these cannot come into play.

Therefore - It is only literally a few places your problem can exist at, if 24vac power is at the transformer, but not at R (if what you reported, is true)