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I have a Goodman furnace model GMP075-3. Yesterday night the furnace stopped producing heat--the blower ran continuously. The diagnostic code was "4 blinks" meaning that the limit circuit was open. I checked all of the rollout limit controls (we had very high winds the night before the furnace stopped heating). After I checked the rollout limits, I restarted the furnace and the diagnostic code changed to "3 blinks." And after about 5 minutes the furnace blower stops.

3 blinks means the pressure/limit switch is malfunctioning. I checked the small rubber hose between the pressure switch and inducer and it seems clear. When I suck on the hose I hear a click in the pressure switch--I assume this is the switch completing the circuit. I checked for obstructions at the inducer and it too seems clear although it doesn't seem to be producing much (if any) suction--meaning that I don't think it's creating enough suction to trigger the pressure switch. I have no way of measuring the vacuum. I place my finger over the end of the inducer's valve and it doensn't "suck" down on my finger (like a vacuum would).

Could it be my pressure switch? Or is it likely the inducer not producing enough vacuum? If I bypass the pressure switch the furnace heats--but it's not safe to keep this bypassed.

Any help would be greatly appreciated.

Thanks,
"Freezing in Ohio"
 

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The most reliable way to check the inducer motor is with a Magnahelic guage. They will pull any where from .5 to 1.25" inches water column (usually stamped or labeled the specification). You can either have a professional check it and see which is malfunctioning or buy a part and change it and see if that fixes it. Depending on how old it is, the part may still be under warranty as Goodmans have a 5 yr. parts warranty on them (you pay labor).
 

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would reccommend mag gauge to know for sure but it sounds like inducer motor.Check for water blockage as well in condesate lines.Also these units had rings popping on the primary x-changers.If you have to manually reset limit around burners{not reccommended} x- changer problems for sure on this unit.Maybe contact goodman for model and serial # s affected
 

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low vacuum at pressure switch

I'm having the same problem - I can suck on the tube to the pressure switches on my gsm060-3 and the furnace will light normally. I replaced one of the switches; no good. I can't sense any vacuum at the venting fan port - even .7 inches of water would be something, I would think. The fan blows hard, but I opened it up to look at it, and I can't see how a measurable vacuum is being generated, although it used to work...

If you figured anything out, let me know.
 

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I'm having the same problem - I can suck on the tube to the pressure switches on my gsm060-3 and the furnace will light normally. I replaced one of the switches; no good. I can't sense any vacuum at the venting fan port - even .7 inches of water would be something, I would think. The fan blows hard, but I opened it up to look at it, and I can't see how a measurable vacuum is being generated, although it used to work...

If you figured anything out, let me know.
More than likly it's the switch, but be sure to replace the hose as well. I have ran into this many times im my area, howerver, if the unit is older, you may have a loose spud (barbed fitting on inducer) had that too. But this is of cors after you tested with didg. mag gage and compared reading to that of the presure switch rating found on back of switch.
 

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would agree with Nikko check water lines ,and yes big probs with ht x-changer if going off on limit.Don't change too many pressure switches.miss diagnost alot of times they are doing there job by not closing,maybe a sag in exhaust vent down the line ,or ventor motor not up too speed
 
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