I have a 4 year old carrier 80k btu 2stage furnace that is cycling on high limit when it runs for an extended period of time.
When the temp on the stat is dropped over night, it will take about 3 hours to gain 3° in the house.
The unit will run for a short while on the first stage and kick up into the second stage which will shut off on high limit after a few minutes.
It happens with or without a filter in place. The duct is sized properly. The A-coil is completely clean. Fan blades are clean and no obstructions. The venter motor is a two stage as well and seems to be running properly. The blower motor is a variable speed ecm and ramps up and down with the first and second stage.
Gas pressure is good, no flame roll out or discolouration, not producing any CO at the exhaust outlet.
Max temp outlet on the rating plate is 185°, the high limit is 170-20 which is located fairly close to the center of heat exchanger. My probe when put into the plenum about 6” above the furnace will reach about 160° when the unit kicks out.
I don’t think I’ve missed anything but I have no idea why this thing is kicking out on high limit. Any suggestions???
When the temp on the stat is dropped over night, it will take about 3 hours to gain 3° in the house.
The unit will run for a short while on the first stage and kick up into the second stage which will shut off on high limit after a few minutes.
It happens with or without a filter in place. The duct is sized properly. The A-coil is completely clean. Fan blades are clean and no obstructions. The venter motor is a two stage as well and seems to be running properly. The blower motor is a variable speed ecm and ramps up and down with the first and second stage.
Gas pressure is good, no flame roll out or discolouration, not producing any CO at the exhaust outlet.
Max temp outlet on the rating plate is 185°, the high limit is 170-20 which is located fairly close to the center of heat exchanger. My probe when put into the plenum about 6” above the furnace will reach about 160° when the unit kicks out.
I don’t think I’ve missed anything but I have no idea why this thing is kicking out on high limit. Any suggestions???
