Comfortmaker upflow furnace M/N GNJ075N16 A1

[TheDuke]

Service call was out here before glow plug ignitor was not liting up so i checked pressure switch it was good so i cleaned plug wire blew in it pluged it in the hit emergency switch it fired up.
watched this thing go off on like 5x make shore that was problem.
two days later a recall ok im thinking faulty pr sw or ignitor.
I call supply house they do not have pressure sw in stock so i call another they don't have that one but person working there says that m/n furnace uses a .50 wc
well i stop there on the way pick one up and a glow plug for unit.
now I go there i look in ohm out glow plug i get over 95 ohms so i know it has to have hair crack in it.
well i watch it cycle on before i change it it glows then second later goes right out, ok i change it look at old one has a hair crack real small like a half cicle on side ok watch it cycle 5x again even suck out orifaces with shop vac make sure i got it, also check pressure switch size on unit it is .40 wc so i don't change it, could it have wrong size pressure switch in it or was supply house wrong on size.
ok 4 days later now this will be my third time out this thing don't have a flame sensor rod has a flame switch also, get these intermitent one drive me nuts think pr switch is right size on it i will call supply again make sure

[Senior Tech]

I believe the one your working with has a "flame rod assembly". However given the limited info you've given about the symptoms it would be difficult to even attempt to assist you....
You have also began your diagnosis prior to actually bring in front of the unit with a meter...monometer...etc. That can be risky at best.

[TheDuke]

75,000 btu input 80 percent eff. year 1995
m/n GNJ075N16 UPFLOW
GLOW PLUG SAME AS PART 41-414
OK like i said it has a .40 wc pr sw in it well i called the dealer again to ask size of the pr sw for that model furnace they said it comes with a .50 wc
guess some one had change it out at one time or another put wrong one in that gotta be it if the flame sw went it would just go would not be intermitent like what it is doing
i guess
all other safetys are good and air filter is clean and inducer working good so is blower motor nothing getting real hot
just gets me when i run accross these ones were i go back few times
thank you for your reply anymore are welcome thank's

[TheDuke]

just thought I would post the end result.
ok no this unit does not have a flame rod.
this unit has a flame switch.
went back today last out there last friday today is monday.
now this is a rental property and the basement lites don't work, did not bring my spot lite with the 30 foot cord this time just my maglite.
changed out the pressure switch with the new one also put in a line to the pr switch.
turned it on from the emergency switch and it fird up waited few minutes blower on then like minute later flame out then after like one minute glow plug lites up flame again.
now after few minutes flame out then few minutes glow plug lites flame on. now i hit the emergency switch checked all the limits two on the blower three more in the burner section one more high limit in the heat exchanger all good wires tight.
just to see if the new .50 wc pressure switch was not closing or popping open i just pulled wires from it put my ohm meter on it hit emergency switch waited few minutes switch stayed closed.
also tryed it with voltage same thing pr switch stayed closed with inducer motor on.
only thing this could be is a limit tripping, pluged up evaporator coil.
I spent a good hr looking at this thing go off and on checked all wiring.
this is the only thing that makes sense to me is a plugged evap causing it to do this.
just one of them calls.
told homeowner they need there evaporator cleaned and, put the old pressure switch back and left
if anyone has any opinions please reply thanks

[hvacprodmgr]

TheDuke,



You have one of the old White Rodgers "Radiant Sense" Ignition systems. These were produced in those furnaces, and a couple other manufacturers, for a very short period of time. Parts for them are obsolete.

Everything you are saying points right to the radiant sensor which is the "box" right below the ignitor.

I would check that switch to make sure it is operating properly.
Unfortunately, that sensor is no longer available, you would have to retrofit the furnace to a General 90 system.

[markwolf]

I never saw where you took a rag & cleaned the window off on the radiant flame sensor,or where you checked for power loss through it.They do not work well when dirty.There are alot of those still out there on different stuff.Tee a magnehelic inline with the pressure switch & verify draft.If the draft is close to cutout point for the pressure switch.I would clean the orifice for the tubing,clean the inducer wheel,& verify the flue is not blocked.I just bought a radiant sensor last year there may be some old stock around if it has been discontinued.It would be a better idea to convert it to a flame rectification safety though.I see alot of loaded up inducer wheels on these,especially if the dryer is leaking lint in the general area or if it is dusty/dirty.