Hello,

I'm new to these forums and came across them because I found someone with a similar problem to mine while searching online. My problem is a bit different, so here goes:

We have a Goodman GMH95 furnace. It is not under warranty as we bought the house with it in place and the previous owner didn't register it as they should have.

The first thing that happened that indicated a problem was a loud noise whenever the ceiling vent kicked on when the furnace was running, this happened for approximately two days. We thought it was the ceiling fan needing to be cleaned and I'm not convinced that isn't the case (it has since been cleaned and runs fine).

The second thing that happened yesterday is the furnace stopped working properly but the loud noise is gone. The blower runs continuously without heat and will not shut off. The LED error code the system is showing is 4 flashes. According to the installers manual this indicates a problem with not enough "conditioned" air moving through the system. The manual says to check the filter for blockage (or if it's dirty), to check the blower, or to check the limit switch.

The filter was just changed at the beginning of November, 2015 and I don't see any visible blockage. I double checked and it's still in great shape. The blower is running continuously and is moving air, so the blower motor and blade seem fine, so that should mean it's the limit switch (according to the manual).
I found this video:

https://youtu.be/UZlHJu9yFVg

that says if the blower is running and you have the four flash error and no heat, it's probably the limit switch. So I pulled the limit switch out and tested it with the multi meter, and the circuit completes. I ordered a new switch just in case because they are cheap, but at this point I'm stumped. Could the switch still be bad despite the circuit working? What else might it be?

I always hope to avoid paying a $200 diagnostic fee so any help is appreciated!

Thanks!

 

Welcome to the forums.

Your furnace is one of the rarer ones in that the high limit switches are manually resettable. According to the wiring diagram.... your furnace has two of them. One of those has tripped due to high heat in the exchanger. The filter is the primary cause. Too many closed registers, blocked return, dirty blower fan, clogged/dirty A/C coil in furnace are also causes.

http://www.goodmanmfg.com/portals/0/pdf/ss/ss-gmh95.pdf

 

Ah, so a couple of follow ups. First, should I try resetting the switches myself? If so, how do I do that (The roll out limit has a reset button, but the primary does not and I thought the roll out would throw a 6 flash error code). Second, should I have someone come out to clean the ducts or try sticking the shop vac down the registers to see if anything gets sucked up? It sounds like I'll probably need someone to come out to help, but I appreciate the follow up.

 

Yes you can reset them, they will have a red button in the center you can push. Most likely they will trip again till you find the problem. Like PJ said make sure all your vents are open and not covered up.

 

Like I mentioned.... it's pretty rare to see manually re-settable limit switches. I have a feeling that was done to protect a possibly questionable heat exchanger design. The diagram shows two. One may be visible.... the other may be hidden.

The roll out switches, which your furnace has two of, are manual reset types which is normal.
You also have another high limit switch called primary limit but that one is self resetting.

 

Ok, I'll do some poking around. I know of at least two exchanges we keep closed in the bathrooms because they really heat up those smaller spaces, but they've been closed since we moved in. I wonder if the Christmas tree skirt is covering the one in the living room and maybe causing havoc there (we haven't taken down Christmas yet, don't judge me). The other thought I had is we have an extra return in the master closet and it's down by the floor so maybe something is blocking it. Thanks for the help. I'll report back if I have success.

 

You need to check the auxiliary limit switches as well

 

Astuff, this was exactly what I needed. I don't know where you found that diagram and information, but it was perfect. The auxiliary limit on the left side of the blower was the problem. I had to remove an apparently unused pipe to get to it, and even then it was tight. Regardless, it turns out the auxiliary limits are only attached by one screw. On the one causing the issue, the screw hole had stretched out and so the limit was hanging loose out of the hole in the blower housing and so was not being properly read. I removed it, flipped it over (using the previously unused hole) and tightened it in no problem. I also put a small piece of duct tape over the unattached side to secure it better and hopefully prevent that from happening to the new screw hole. I closed things up and turned it on and voila! Fired right up. Thank you all for your help. I hope someone else having a similar problem will find this post someday. Cheers!

 

Well darn, the same auxiliary limit keeps flipping. Not both, just the one that was loose. Its still on tight but it keeps flipping. Wouldn't they both flip if there was a problem? A bit confused.

 

Those are limit switches that are designed to trip when they exceed a set temperature. The aux switches are there to stop the burner when the blower compartment gets too warm with the theory that the fan has stopped moving air.

With an attic system in a horizontal position the top one would trip first as heat rises. You may just have a bad switch - try swapping the two on the blower.

The full service manual:
http://www.alpinehomeair.com/related...3%204.2013.pdf
It does say: