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goodman furnace short cycling.

meticulousmikemeticulousmike Member Posts: 31
edited February 19 in Controls
hi all,i hope i'm posting in the right spot.sorry i haven't replied back in the strictly steam category for a problem i had there..the landlord has not called me back over to correct the issue with some of the answers some of you guys gave me,so i haven't been able to do the work to see if it fixes it or not.he hasn't complained either about any lwco issues,hammering or spitting steam mains.so i'm going to assume that he doesn't want to correct the issues yet.i gave him the complete replies to my question so that he could see for himself that i'm not telling him stuff that i'm just making up.anyway i got another issue with a goodman furnace model gmpo75-3 it's a 1991 unit.jumping at unit with tstat out of line it fires up and runs for minutes at a time.i didn't actually time it.then it fires off after so many minutes with the inducer still running and then goes for another firing sequence,runs and then fires off again.it's not intermittent it stays constant with the short cycling .it will run for many minutes and then repeats the cycle.there are no codes being flashed.after it went off i turn the power off and try to pull the wires of of the high limit as fast as i could to see if the switch is still closed,it is,.then i do the same for the aux limit,same thing.i cleaned the flame sensor and still the same thing.short cycles with no code flash.i also tried to get a continuity reading off of the gas solenoid.i get continuity.what i don't think i tried was keeping the 2 wires connected to the gc while it is running to get an ac volt steady reading and carefully watch to see if there is a dip in volts suddenly, briefly or something..correct me if i'm wrong but i eventually came to a conclusion years back on some other IFC on a furnace is that ifc's can't diagnose them selves to see if there's an error on the board,just like car computers, i believe.there are some if not all ifc's that will indicate it's malfunctioning by not lighting up at all which tells you it's either a power issue ie; popped breaker or blown fuse,transformer,etc,blown ifc fuse,if present ,etc.or just malfunctioning altogether but not a specific part on the board that's malfunctioning.time to replace the ifc..i think i did a flame rod dc check,i think the tsat was not connected to the system-this was many months ago so i forgot those details.i wrote everything else down but not those specifics...so i'm stuck thinking that it's either the ifc , gas control or flame rod or maybe all are the culprit(s).i don't know how to test the gc on this type of situation.if i need to,what is the procedure?i was told that i can't diagnose a ifc in the field so i won't be trying to do that.what is the problem with this thing?...i forgot to mention that months ago it was a no start call that was corrected.turns out that the hot wire off of the main service switch was arcing to ground inside the switch box that was mounted to the supply plenum ductwork..the previous repair guy or the installer didn't properly connect the wire to the switch terminal or it rubbed through.i guess.when the blower came on it vibrated the heck out of the box and then the heat transferred into the box, expanded and caused havoc...any help will do thanks for the reply(ies) in advance. gas control rob shaw grayson 72001per. 7e3-d58-029 in case you need to know.
drain cleaning, plumbing,heating and electrical repairs.

Comments

  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,058
    Take the wires off the limit control, and jump them together then start the furnace and see if it runs.

    If it's not the limit shutting the furnace down, take the wires off the air switch. Start the furnace then jump the air switch wires together. and see if it runs.

    DO NOT run the furnace without a functioning limit or a function air switch. This is for testing only.

    Did you check the blower to make sure it is operational??
  • HVACNUTHVACNUT Member Posts: 3,369
    Is the air filter clean? Evap coil if there is one?
  • rick in Alaskarick in Alaska Member Posts: 1,082
    Sounds like one I was just on. Unit would run for 3-4 minutes, then flame out and cool down, then start right over again. After checking limit switches. I finally found it to be shutting off on high limit, and then determined it was running over 160 degrees on the outlet temp. That is when my coffee finally kicked in and I paid attention to the whole picture and realized it was a 117,000 btu output furnace in a 1600 square foot space, and being fed with an 8 x 18 return. I let them know we will either have to change the furnace out, or it will just keep short cycling. Waiting on that call.
    It sounds like you have checked the high limit switch and it is not kicking out, so the next thing would be to check the flame rod and see what reading you are getting. I, however, am not certain if your furnace will just keep recycling itself if it senses a bad flame reading without throwing an error code.
    Rick
  • meticulousmikemeticulousmike Member Posts: 31
    i checked if it was the high limit,it didn't shut down because of that but the aux limit was still in there so i gotta somehow figure out how to get to it and disconnect it without having to pull the blower out.obviously the blower is operational and working..i would have said that in my post.

    Sounds like one I was just on. Unit would run for 3-4 minutes, then flame out and cool down, then start right over again. After checking limit switches. I finally found it to be shutting off on high limit, and then determined it was running over 160 degrees on the outlet temp. That is when my coffee finally kicked in and I paid attention to the whole picture and realized it was a 117,000 btu output furnace in a 1600 square foot space, and being fed with an 8 x 18 return. I let them know we will either have to change the furnace out, or it will just keep short cycling. Waiting on that call.
    It sounds like you have checked the high limit switch and it is not kicking out, so the next thing would be to check the flame rod and see what reading you are getting. I, however, am not certain if your furnace will just keep recycling itself if it senses a bad flame reading without throwing an error code.
    Rick

    you can try and cut a wide 'cheater' return as i like to call it. in the trunk of a rigid professionally made return duct if it is one and if there's room for it or on the backside or side of the unit.filter rack it and your done.the only issue would be is that there is an extra filter to have to change and less money in your pocket unless you want to go adding more ductwork or modding what's there. i always thought that there should only be one return on a system.i was told by this young licensed hvac tech that there can be 2.i didn't ask him if there could be more.something i didn't know.anyway the above mentioned got me out of having to tear open by the front doorway and end of the stair railing a bigger hole in the floor for a wider return.worst place to put a return is in the floor especially at the bottom of a staircase and front door of a house..yes good because of a cold drafty door but not good cause of all the garbage that gets sucked in there.i kept getting the high limit break.i kept telling the landlord and the tenants that it was over sized for the size of the house,,it had a cob job supply plenum ductwork with undersized round pipe and small registers,the return grill in the floor and round pipe leading to the pro made wide curved return duct was too small too.the unit should be running fire continuously without interruption until the tstat is satisfied.
    drain cleaning, plumbing,heating and electrical repairs.
  • icy78icy78 Member Posts: 351
    Post a steady state combustion analysis. (Flue draft included)
    Temperature rise.

    Does it have a trap with a drain sensor in it and you have a slow draining trap possibly?
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