Goodman GMP075 tripping brakers!! Help!


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Old 02-11-09, 05:46 PM
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Goodman GMP075 tripping brakers!! Help!

My GMP075 is causing the breaker to the furnace to trip. When the breaker's reset, the furnace will act as normal (draft fan OK,Ignitor OK, gas valve OK, Circulation fan OK) but will only run for about 15-20 seconds then trip the breaker (20 amp.) It's not blowing the 3 amp fuse on the board either. This thing was running fine for the last few days since I replaced the high limit switch but now it's doing this.

There are no codes flashing but then the power goes out when the breaker trips so when I reset the breaker, the light's steady. What should I be looking at? There's no smell, no sparks, no flash. It just shuts down the breaker.

Any suggestions? QUICK??
 
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Old 02-11-09, 05:55 PM
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You wouldn't happen to own an ampmeter would you? That would take the guess out of if there really is a high amp draw, or something wrong with the breaker.

Or if you are a decent electrician, you could swap out your furnace wire from one 15 amp breaker to another, in your panel box, and see if that one trips.
 
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Old 02-11-09, 05:59 PM
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It's not the breaker. I just got back from Menard's with a new one. Something's causing it to trip. I think I've got a multimeter around here somewhere.

Where should I be looking for a short or whatever?
 
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Old 02-11-09, 06:15 PM
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I'd check the two biggest users: The blower motor and the inducer motor. Check for any kind of short from hot motor wire to metal casing of motor, with an ohms test, with furnace turned off. If motors are good, there should be no reading. None. If there is a little, you may have something when the motor turns that the little becomes big, sometimes.

Open both the blower door(tape the interlock switch so furnace still can run) and the combustion compartment door, and lsiten to furnace carefully, and see if you hear anything out of the ordinary, like a drag on either motor, when it shuts off.

Other than lucking out with either of these, this may be a tough one.


What makes this tough is the fact that your entire furnace sequence occurs, and stays running as long as it does. If say the circuit blew right as the blower came on, or whatever, then you'd know.

You may end up having to have an ampmeter, and clamp it around the 15 amp breaker wire, to see when during the running of the furnace, if you get a spike in amps. Or if it is high from the get go. This may help steer you onto something.
 

Last edited by ecman51; 02-11-09 at 06:25 PM. Reason: added last 2 paragraphs
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Old 02-11-09, 06:25 PM
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Also check the high voltage connections at the furnace, wire nuts switch screws etc., as a loose wiring connection in high voltage can cause a high amp draw. Check neutral and hot wires.
 
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Old 02-11-09, 06:25 PM
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$#!T.

OK, the blower door is already off and I've already taped the interlock switch so I could see if anything obvious was happening. I didn't hear anything out of the ordinary when it shut off, the fans sounded like they always do. If a fan can cause it though, I suspect it may be the blower motor. It's a bear to get to but there are some leads to a relay just next to the transformer. Are those the ones I should be looking at to check the motor?

I'm gonna check them both for a load. I assume I should be checking this with the power on, right? Or does it matter?
 
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Old 02-11-09, 06:44 PM
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Alright...one more night like this and I'm putting in friggin 220 electric baseboards until Spring.

I'm not getting any multimeter readings from either motor. It was my intention to replace this bugger in the Spring anyway (it's about 24 years old) so I'm seriously considering a trip to Menard's for baseboards in the morning.

Talk me down. Where else should I be looking?
 
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Old 02-11-09, 06:50 PM
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How are you testing (how are you hooking up your test leads -to what)? And what are you testing for?: Volts? Ohms?

I have to leave, so make it quick, please.

I see you have not responded yet. If you have enough money for baseboard heater, endulge in new toy, and buy ampmeter, so you can find out if you have a spike during the operation sequence, or just a plain high read from get-go.

Observe furnace in pitch-black dark to see if when furnace shuts off you see a spark occur, say as fan switch shuts off. Maybe that is where your problem lies. And if it is, let's say, the ampmeter would show a sudden spike at shut-off.

Make sure your furnace is designated on that one circuit!! If someone cheated, and you have other stuff on the circuit............
 

Last edited by ecman51; 02-11-09 at 07:09 PM. Reason: added more while waiting
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Old 02-11-09, 07:10 PM
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My usual method for identifying shorts is to 1) either disconnect everything and add portions of the furnace system back one by one until I find the one that causes the short or 2) pick likely prospects for a problem, like the fan motor and disconnect that and see if the furnace quits shorting out.

Of course if you leave the furnace burning long enough without the fan running, the burners will shut off on the limit switch.

One of these two methods generally works pretty well for me.
 
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Old 02-11-09, 07:11 PM
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Sorry, EC. I was under the house again.

I'll buy the ampmeter AND the baseboards tomorrow. Altogether, it'll cost less than $300 and I'll keep them installed as a backup for whatever furnace I replace this one with.

As you can tell, I'm kinda disgusted and pissed off at this thing right now.

Enjoy your evening.
 
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Old 02-11-09, 07:32 PM
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Another way to test the blower motor would be to wire it into an extension cord plugged into another circuit and run it for a while to see if it operates properly or shorts out.

If you have a way to turn on and run the fan munally, you could try that as well and see if the fan operates properly when just it is running.
 
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Old 02-12-09, 07:37 AM
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I see in you first post you say you have a **20**amp fuse. I am saying that again since you never acknowledged that part of my earlier post.

Normally 15 is what is used. Be sure you make sure nothing else is on that circuit before you go through all the work. If you have 2 wires coming off the circuit breaker, right there you'd know for sure. But even if you do not - unless you physically trace say one wire only from circuit breaker to furnace, with no junction boxes in line, you won't know.
 
 

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