Please help troubleshoot nat gas Goodman furnace. Power on. Fan/blower runs constantly, but no heat. No flame. 4 blinks. No manual, but I believe this to mean "open limit" by reading other posts for this model furnace. Furnace filter was very dirty and has been replaced.

Traced wires back to what I believe is limit switch. (see image #1 in image. 2 screws removed so it is it half uninstalled and titled horizontally instead of vertically.)
swtichornot.jpg picture by mypicstrix - Photobucket

From the front, linked image below seems to match mine very well. Switch model numbers match.
Service limit switch - Product Details

However, instead of wires going out the back there is a hard black plastic rod shaped like a rocket popsicle. Maybe this is a cover? Is it removable? The limit switch has two screws which I have removed, but I am unable to wedge or angle it in such a way that it is removable. I maybe have to remove a few screws from the plate housing that holds the fan before I fully uninstall the limit switch.

Does this switch model have a reset switch?
http://ww2.justanswer.com/uploads/Ou...nual_reset.jpg

So is this just a fuse with a sensor? If I short the wires (only for test) would the furnace run with heat?

Do big box stores have these limit switches? What kind of stores would have these or sell HAVC equipment? We are using electric heaters enough to keep things livable, but it's winter here, so help is appreciated!

Thanks.

UPDATE: As a test I've closed circuit and tested it. Flame does come on and everything appears to work normally. I guess that's a confirmation

It was tricky getting it out, but here it is:
switch00.jpg picture by mypicstrix - Photobucket

Looks like the same animal as the link I showed above, but it certainly is a different design.

I found a place to get a replacement... Can any of you guys confirm this is the problem and replacement switch its correct?

Thanks

UPDATE: As a test I've closed circuit and tested it. Flame does come on and everything appears to work normally. I guess that's a confirmation

It was tricky getting it out, but here it is:
switch00.jpg picture by mypicstrix - Photobucket

Looks like the same animal as the link I showed above, but it certainly is a different design.

I found a place to get a replacement... Can any of you guys confirm this is the problem and replacement switch its correct?

Thanks

No,, would be hard to confirm without being there, these switches don`t go bad that often,, I would wonder what is causing the furnace to overheat and cause the switch to open, you will be lucky to find a dealer that will sell you (non-contractor) any part,and if you do it won`t have a warranty,, again what is causing the furnace to overheat? Did you confirm that all vents (supply and return) are open and clear
Goodluck

As I said, the furnace filter was very dirty so I think that might have been it. Past posts on this topic seem to suggest this is a possible cause. We had a power failure for about 15 minutes but furnace never fired again. In fact, it's possible it cut before power failure and I just didn't notice. I recently installed a humidifier so prior to this the fan has been running a lot to move the moisture, sometimes without heat. Humidifier required I reroute the (G) Green wire from thermostat through the humidifier before connecting to furnace. The flashing trouble light on humidifier was the first thing to draw my attention because it thought the HVAC was off. One other variable is that I recently hooked up the "C" (blue) wire from my furnace to my thermostat so that it's powered and can just use the batteries for backup. I have no idea if any of this is relevant. I'm going to blame the air filter and my own negligence. I forgot we were using a more hyper allergenic (thicker) filter so it got dirty much faster than the fiberglass ones I usually use. Still, my own fault. I'm back to fiberglass now which I hear is better for furnace longevity anyway.

Anyway, just got back from some a part store where they do HVAC installs and repair. If you find yourself looking for parts, call your local hardware store. Even if they don't sell furnace parts, chances are they've been asked before and will know where to direct you. Of course if it's a big box hardware/lumber store, then they will probably have no idea. Try Mom&Pop. I bought the switch for same price as I found it online. For those who happen to have this same problem, don't worry if your original switch looks a little differently with the black housing. Back side of new model is just the wires with the sensor. Also, if you have trouble installing/uninstalling, try going UNDER the black pipe gas supply instead of over it. That worked for me. It was a tight fit, but there was no need to remove any other parts.

So anyway, problem solved. I'll be holding my breath for a day or two, but I think I'm okay now.

I know no one responded in enough time to help me, but older posts from this same forum were VERY helpful, especially from Hvac1000. Glad I had this resource or else I'm sure I'd be out some good money for the service call. In fact, anyone know about what service call like this would cost? Come out, troubleshoot, and replace switch? I'd like to be able to tell the wife how much she saved after she's sees what a mess I made in the garage.

BTW, if anyone knows where I can get a manual for my GMP075-3 Rev B Goodman Natural Gas furnace, please let me know. I've looked everywhere I could think of online, but no luck.

Thanks.

Here is your manual

http://www.hvacpartsshop.com/Gmph075-4%20Series.Pdf

This manual covers all service aspects for your furnace BUT it also contains info for other model numbers also. As you go through the manual always keep in mind that you need to use the information for your model.

I saw your posting but I felt you were on the right track and needed no interference from me to make your decisions. This way you can actually say you fixed it yourself.

One note about parts.

Parts are made by many different manufactures that do the same thing and those parts are available from many different sources. The main item on parts is to be sure they work the same way, the setting and insertion length etc. is the same. The manufacturer selects parts based on the need to do a job in the unit and COST. If they can find a cheaper part they will use it since that keeps the cost of manufacturing down. During my years in the service arena my company only tried to use OEM or original equipment parts when ever possible in strategic areas. Especially areas where failure of the replacement part could put me in a court of law (read wrongful death law suit etc.). This was done for my corporate self preservation as well as the good of my employees since no one is exempt in a law suit. The employee who bolts that part in is just as responsible as the company when it comes to items like this as has been proven by the law time and time again. The standard lawyer language goes like (John Doe an employee of XYZ Company was a professional and should have known better) or sum such wording. For the most part that is why I like to recommend exact replacement parts whenever possible since a liability issue can follow. Now with you doing your own work buying your own parts just about the only person your wife could sue is you and you are a dead man since the furnace blew up or killed the family with CO. LOL

I am glad to see you figured it all out and you are back in operation. Service call, labor and retail parts could have been an easy 250.00 or 300.00 so beat on your chest a bit and tell the wife you deserve and beer and a back rub for all the money you saved the family. You never know you might get lucky.

Attached Images

 

Hvac1000,

Thanks for your help. Other than maintenance cleaning I had pretty much zero knowledge of furnaces at the start of all this so, as I mentioned, your old troubleshooting posts were a lifesaver. Things are still running smooth, BTW.

All I know about the part I did get is that it matched the model number of the original and was sold to me by a local mom&pop establishment that installs and maintains HVACs for a living. I understand the liability aspects, but unless you have a red flag to throw up, I don't see any reason to doubt the safety of the part. I imagine these sensors have been made a long time across many brands.

The $250 pat on my own back isn't as sweet knowing it was my negligence that let the filter get dirty so long. Ha ha. (Wife doesn't have to know that part)

Oh, the pdf manual you linked is dead. I'll try it again later, but if you have another home for it, please post.

Thanks again Hvac1000. Glad you're here.

Pete

Check the link tomorrow. It is a good site and the links are always good but the site might be down for maintaince.

On the filter thing. It is easy for people to forget so mark callender for every 2 months or use the outlook computer program to get reminder.

Was able to get manual today. Thanks!

I just hit the manual site and it loaded perfectly.
Could the problem be on your end?
It is way to big to post here. 77 pages Try the link below. It is the same link but a fresh post.

http://www.hvacpartsshop.com/Gmph075-4%20Series.Pdf

Meant to indicate that I "was able to get manual today". I DID get it. Thanks for all your help.

Ok