Goodman Main Limit Operation?
#1
09-21-20, 12:15 PM
Goodman Main Limit Operation?
Hello All:
I've looked around on various sites including this one and can't seem to find a clear cut answer so I appreciate any insight you can provide.
I'm running a Goodman GMPN108-4 gas furnace, about 20 years old. I live in upstate New York (read: cold). I'm running a Nest thermostat.
Anyway my question is, is it normal operation for the limit switch to trip during a heating cycle or should it never trip unless something is wrong? I think ever since I've moved into this house (8 years ago), the furnace kicks on, runs for a bit, then the limit switch kicks the flame off and it cycles on again once it cools down.
I realize this suggests an airflow issue, but before I dig into the return air ducts and warm air side, blower, etc I just wanted to confirm that the main limit switch isn't a normal part of the heating cycle. The reason I ask is I replaced the OEM limit switch years ago with an adjustable Honeywell model so maybe that setting is too low (it is currently set on 180, I might try 200), but again before I change anything I wanted to confirm that this wasn't normal operation. Thanks for taking the time to read this and respond.
I've looked around on various sites including this one and can't seem to find a clear cut answer so I appreciate any insight you can provide.
I'm running a Goodman GMPN108-4 gas furnace, about 20 years old. I live in upstate New York (read: cold). I'm running a Nest thermostat.
Anyway my question is, is it normal operation for the limit switch to trip during a heating cycle or should it never trip unless something is wrong? I think ever since I've moved into this house (8 years ago), the furnace kicks on, runs for a bit, then the limit switch kicks the flame off and it cycles on again once it cools down.
I realize this suggests an airflow issue, but before I dig into the return air ducts and warm air side, blower, etc I just wanted to confirm that the main limit switch isn't a normal part of the heating cycle. The reason I ask is I replaced the OEM limit switch years ago with an adjustable Honeywell model so maybe that setting is too low (it is currently set on 180, I might try 200), but again before I change anything I wanted to confirm that this wasn't normal operation. Thanks for taking the time to read this and respond.
#2
09-21-20, 01:13 PM
Member
Hi, certainly not normal operation, limit switches are safety devices, what was the original limit switch set at, you should not exceed that, are the your supply registers open, filters clean , fan speed correct?
Geo🇺🇸
Geo🇺🇸
#3
09-21-20, 01:24 PM
Thanks for your quick response. Original switch was 170, so I'll make sure not to move it to 200, good call. Yep all supply registers are unobstructed, filters are clean. Fan speed seems correct, I keep the fan on continually and haven't noticed a decrease in air volume or different sounds to indicate failure or blockage.
I had a new AC unit installed this summer then later on had a new blower motor installed as well. I'm not sure if maybe the new evaporator coil is restricting air flow. I'm assuming the installer would have put something in that was compatible with my system but you know what they say about assuming...
I had a new AC unit installed this summer then later on had a new blower motor installed as well. I'm not sure if maybe the new evaporator coil is restricting air flow. I'm assuming the installer would have put something in that was compatible with my system but you know what they say about assuming...
#4
09-21-20, 02:24 PM
Group Moderator
Welcome to the forums.
Yes.... I wouldn't recommend going over the factory temperature rating. That thermostat protects the heat exchanger from over heating.
The new evaporator coil could impede the flow. Your installer should have checked the heat rise after the A/C installation. You may need to increase the heating blower speed.
Yes.... I wouldn't recommend going over the factory temperature rating. That thermostat protects the heat exchanger from over heating.
The new evaporator coil could impede the flow. Your installer should have checked the heat rise after the A/C installation. You may need to increase the heating blower speed.
#6
09-22-20, 07:08 AM
In my original post I mentioned it always happened, but it never went into lockout before so I think this is new. I opened up all the warm side vents and made sure the cold air returns are unobstructed. This seemed to help this morning when the furnace was trying to catch up from overnight. It may have been a mixture of factors that caused the lockout, I put new less restrictive filters in, had vents still closed from AC operation and with the new coil this may have just pushed everything over the edge. Today I am going to crank it up and watch the limit switch to see what happens. Thank you for the insight and for helping to bounce ideas around.
