nordyne tripping limit

[iowa tech]

model m3rl080a
ser m3a050301139

keeps tripping limit on combustion blower
work alright while i there
something over heating but what
any help?

[gravity]

is this a 90%?

[rundawg]

model m3rl080a
ser m3a050301139

keeps tripping limit on combustion blower
work alright while i there
something over heating but what
any help?

I would first pull the inducer motor off and check to see if the restrictor plate (inducer orifice as they call it) is damaged, eaten away, or has fallen out.

If the inducer is pulling too much flue gas through the orifice, the gas is not having enough time to cool off by staying in the HX long enough.

You can also put a temp probe in to see if the flue temp is above 145ºf to eliminate the possibility of a bad switch.

The part number for the orifice on the 80,000 btu unit is #155315R.

[iowa tech]

Temp is about 135 in flue
New c blower install by first tech
Yes 90%

[rundawg]

Temp is about 135 in flue

135ºf flue temp is tripping a 145º limit.

How far away from the inducer did you measure the temp?

Assuming you are confident of your temp reading, and the 135ºf flue temp is stable, I would be installing a new limit.

A combustion analysis would help in determining if the readings are stable.

[BigBacardi]

i remember my first time with a problem similar....the disc was so rotten that it wasnt there. i was pulling my hair outa head untill some other guy said that the opening should be 1.5 inches.....i said its about 3.... disc wasnt even there or any signs of it...hahahaha

couple months later i go to similar call....new apprentice was like omg u so smart...lol i told him the long version....he laughed....

[gravity]

135* flue temp.

combustion analysis would help determine whats going on. 135* is max you want on a 90% furn

check air supply blower wheel and secondary heat exchanger. Make sure your moving enough return air. usually low airflow or overfired causes flue temp to be that high.

you need 150cfm per 10,000 input btu with 90% furnace.

[Chuck]

i remember my first time with a problem similar....the disc was so rotten that it wasnt there. i was pulling my hair outa head untill some other guy said that the opening should be 1.5 inches.....i said its about 3.... disc wasnt even there or any signs of it...hahahaha

couple months later i go to similar call....new apprentice was like omg u so smart...lol i told him the long version....he laughed....

I find a lot of these m3 furnaces with inducer limit tripped. To date, every one was due to corroded or missing orifice.

[Joehvac25]

I find a lot of these m3 furnaces with inducer limit tripped. To date, every one was due to corroded or missing orifice.

Invaluable information, thanks, hear of this one time only but the other tech never found the issue that I know of.

[DeHeatify]

Orifice.. one for the memory banks...

Sent from my SGH-I747M using Tapatalk 2

[Joehvac25]

The older Lennox ghr 26 had them also.

[Chuck]

The older Lennox ghr 26 had them also.

Yes. Did you ever see one of those corroded? They obviously used better material.

[Joehvac25]

Yes. Did you ever see one of those corroded? They obviously used better material.

No but I have seen the condensate box come apart and not close ps switch. Inside of it i mean. The old discs always seem fine in the inducer!