NEXT STEPS OF TESTING, PLEASE? Pressure Switch or Limit??


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Old 11-09-13, 04:53 PM
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NEXT STEPS OF TESTING, PLEASE? Pressure Switch or Limit??

Hi There,

I have a Goodman GMP 125-5 gas furnace (probably about 7-8 years old or so) and have been gone for a few months overseas, and when I came back, my furnace was not working properly. I have never ever had any issues with it thus far and was fine when I left. I tried turning the heater on and the blower comes on but the hot surface ignitor does not glow red and there is no flame being lit. I just replaced the ignitor today and still the same problem (also tested new part with multimeter and part is good). The sequence that I have noted is that the blower comes on (thermostat properly responds when I set it), then i hear a clicking noise (think that is the gas opening), and this is followed by the gas being fed to the burners.
However, the gas continues on for a few seconds, then shuts off, then after a few seconds attempts to give more gas again, and since nothing ignites (no heated HSI), the unit just stops altogether after a few tries/cycles of this, and all the while the blower is running. I can smell the gas and the valve was not turned off when I left town, so it remains open. Also, I am getting a code reading of a continuous blinking light (blinks on and off over and again, which I just believe is showing that the unit had failed attempts, but not really telling me anything more specific).

It is cold here and I'm not sure of the next step. I had even manually lit the burners twice, in the beginning thinking there was just some build-up on the components and that it could burn off. The heater stayed on for a few minutes, and then turned off. I think with the intermittent pilot for energy-saving, when the pilot went out it tried to reheat and couldn't, since the hot surface ignitor was not coming on and I didn't manually light it again. Oh, I also checked my flame sensor and lightly sanded it for cleaning as a good measure (even though there is no flame to detect at this point).
I checked the thermostat and it is fine, although there was a spark at the thermostat twice in my initial checks of the furnace when I got home and switched one side to auto (the other was already in the "heat" position). I completely took the t-stat apart and made sure there were no bad connections or burned wires, and everything is good there, but still puzzled as to why it sparked in the first place.
I would like to conduct some other electrical tests but am having problems removing contacts from my limit and pressure components. It seems that I may break the tabs/prongs if I wiggle or pull too much harder, but that may be what I have to do. Lastly, I am not sure if it would be more beneficial to test the air pressure (already removed hose and blew in- no obstructions that I can tell) or the limit control next. If the gas valve is opening and sending out gas, is the next process in the sequence related to the pressure switch? I think I hit some resets, but not sure if that is what they were. There were three pop-up type buttons throughout the unit (think they were connected to the limit components) and I pressed them, even though they didn't seem to really depress much (probably indicating they didn't need resetting), and I also changed out my three filters- two were pretty dirty and the other not so bad.

Thank you so much to anyone out there who could possibly help me to get some heat again! I have already done a lot of troubleshooting and about as much as I know to do not being in the HVAC business and having further knowledge. I have a good multimeter and with guidance can perform some other tests (no jumper wires, though). The code interpretation would also be most helpful, as I still don't know what the problem is.... Thanks so much!
Lori
 
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Old 11-09-13, 11:38 PM
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Turn off the gas to your furnace and measure for voltage to the ignitor after the power ventor runs but before the click of 24 volts ac to the gas valve.

If you do not get power and the wires are plugged into the correct location on the board, replace the board.
 
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Old 11-13-13, 12:53 AM
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Hi Houston 204,

I'm very appreciative for your reply and help on this one. I did check for voltage, exactly as you suggested and am in fact getting power to the ignitor. Is there anything else that you would suggest I check or that would stop the new and perfectly good (and tested) ignitor from starting? Our temps here just dropped last night into the 30s and 40s and I'm racing against the clock for a potential freeze. Again, I appreciate any and all feedback and the test of power shows to be working. Thanks! Lori
 
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Old 11-13-13, 08:17 AM
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Here is a link to some info that may be of benefit to you;

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

You stated you cleaned the hose between the inducer motor and the pressure switch. Check the port where the hose attaches to the inducer motor. It commonly gets clogged up with debris and prevents proper operation of the pressure switch. You can use a paper clip or small drill bit or allen wrench to clear the debris out of the port. Make sure you clean it all the way from the opening to the fan blades in the inducer. When done attach the hose to the port and blow into it to make sure you got it completely cleaned out. Re-attach hose and re-test furnace.
 
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Old 11-13-13, 08:49 AM
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Where did you check for power to the ignitor? If there is 120VAC at the ignitor wires and it doesn't glow, then that ignitor--old or new--is bad.
 
 

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