I wanted to get some expert opinion on this. I have been having an issue with one of my Goodman Furnaces (GMS9) and decided to tackle the simple things on my own.

The initial symptom of a problem was furnace wouldn't light and would error out with "4 blinks" - high limit error. I first made sure air flow was good by checking basics (new filter, inspect A-coil, and main fan) and all checked out clean. I also had no vents closed and flow seemed ok.

I then went down and tapped the high limit with a screw driver and it fired up fine. I have since replaced the high limit switch, both pressure switches and cleaned the flame sensor and the furnace fires up every time but does some strange "short cycling" without any lockout and/or error code.

I've attached a video of it doing it.

I'm thinking that I may have a real issue that is causing the heat sensor to trip but would it clear that fast and fire up like in the video?

Thanks for any opinions on this! Have a great new Year

https://photos.app.goo.gl/rbTjSVKyfqeVgxqPA

 

What kind of thermostat are you using?

You can bypass it by setting it to off and jumpering terminals R and W at the board.

 

I'm using a Delmarva Power programmable thermostat. I attached a picture.

Here is something else odd. I noticed that when we set the thermostat to lower temps (say 65) that everything works fine. When we set it to higher temps (say 70) is when we notice the cycling. This is what is making me thing it's related to the high temp switch but it doesn't error out.....

 

Normally, it takes the limit a while to reset and there's an error code.

By following my instructions, you can rule out the thermostat and it's wiring.

Then go further with a multi-meter - checking the safeties and incoming voltage.

 

I'd rather not jumper thermostat. I have a call out to my power company to replace it to see if that's the cause.

 

You don't replace parts to see if they're bad. Stats are rarely bad - it's just process of elimination, making sure there's a continuous call for heat when it drops out.

If it was giving an error code when dropping out, the troubleshooting would be different.

If you're not comfortable working on your equipment, call a tech out, not your power company.

 

Thanks for the information and I appreciate your input.

I called the power company because we are on a "cycle" plan where they cycle my heat/AC on power saver days. Since we are on this plan then installed and give us these stats. It's their hardware and they are responsible for it. In my situation, it actually makes sense to contact my power company.

I may just take it off and put on an old stat that I have which has a mercury switch :-).

Let say I was to jumper the cables like you mentioned (or put in a new stat) and the same problem occurred. What would be your next step in your process of elimination?

Thanks again!

 

You don’t have to start installing other thermostats or even install jumpers. Use your meter.
If you check and find your getting a continuous call then you’d start checking safety switches to see if any are opening.

 

New development. It shut down again with the 4 blinks error so I cut power and tried again. During it's attempt I wiggled the main harness to the IFC and the error condition went away and it fired up like normal.

So, it appears I have sort of short or a bad IFC. I guess its time to call the professional to come take a look.

 

In case anyone is following this. I just replaced the IFC and it has corrected all issues. Looks like there was some issue with the board itself.

 

It could have been a board problem but it doesn't sound like it. Sounds more like corroded or loose pins in the nine pin connector that connects to the board.

 

Humm...so if you are right then I guess I'll have the issue again. I haven't as of yet so I have my fingers crossed.

Lets say it is loose or corroded pins, whats the best way to go about troubleshooting that and fixing?

Happy New year!

 

So, I hate to say it but I started having issues again. Similar issue but they are different and we never get any error on the board.

see video below...problems start around the 2:00 mark in the video.
https://photos.app.goo.gl/gWuBJhoqDEGNpb1x9

Thoughts? Thanks!

 

Anyone ever seen an intermittent issue like this before? I guess it could be an issue where the inducer fan is getting ready to fail and not drawing enough suction to keep the vacuum switch engaged all the time? I can't reproduce this when the HVAC guy is here and I'm afraid to let it run without being watched incase it goes into the issue.

 

UPDATE

I've had to HVAC technicians out and here were the results.

1. First guy comes out turns on the furnace and watches it for 30 minutes. Doesn't test a thing and says he can't do anything without seeing the problem. He says to call him immediately when it starts acting up again and he'll try to come out ASAP. Charged us 129 bucks.....we didn't call him back as he did not have a manometer. Seems odd that he doesn't have the tools of the trade.

2. Second HVAC guy comes out and when he gets here the problem is occurring. He says wow I've never seen this in my 20 years of working on furnaces. He test gas pressure, and drains and says thats all good. He then says inducer sounds bad and is pulling 3amps so he's pretty sure that's the issue. I looked up the inducer and it's says the draw should be 2.8amps. He wanted to charge us $650 bucks to replace the inducer and could not promise that was the issue. Nor could he tell us what happens if we pay the $650 and then a new inducer doesn't correct the issue. He also did not have a manometer to check negative pressure from the inducer to the pressure switch.

I've ordered the inducer fan (100 bucks) and will replace it myself. Hopefully this is the issue.

So beyond frustrated with this issue. I'd love to find a qualified technician in Maryland to pay to actually test out this issue and fix it.

 

inducer problem won't produce a high limit error. You would be getting a pressure switch error if the inducer was the culprit.

Did anyone check the voltage drop across the high limit when the problem occurs?

What about doing the same at the molex connector for wire leads that go to the limit.

I'm betting it's an issue with the molex connector, connector on board or the board.

 

Since the board was replaced..... good chance it's the 9-12 pin connector. Unplug it from the board and spray the plug lightly with contact cleaner. WD-40 would work if that's all that was on hand. Put the plug in and out a few times to work the cleaner into the pins. Don't hesitate to try it again.

I'm not sure if that inducer is causing a problem but it does have bad bearings.
That's what that loud whine is.