Hi there,
I have a vintage Lennox GH5-75M forced air gas furnace and need a little advice as to whether it is running correctly. I recently cleaned up the furnace from all the dust and cut off some wire that goes from the blower motor to the fixed limit switch to the good part that was exposed because the plastic covering was brittle and flaking off. I re-attached the good part to the limit switch. This is a pretty old furnace but seems to be running ok. It has a separate fixed limit switch and a fan off switch which has temp settings on it. It is set to 120F. I noticed the furnace ran a little off before I cleaned it up. The blower, it seems, would cycle on again about a min after the the furnace finishes a cycle. It would stay on for less than a minute before it shuts off. I'm pretty sure only the blower goes on and not the burner. After the cleaning and wire fix, the furnace ran fine for a couple days but tonight I noticed it did the quick short cycle again.
When it runs fine the thermostat would call for heat and the burners light for about a couple minutes before the blower/fan kicks on. The furnace would run until temp is reached and then the burners would shut off but the blower/fan stays on for another 2-3 mins before shutting off. The cycle repeats when thermostat calls for heat again.
I noticed now, the blower/fan would kick on a min or 2 after a cycle finishes and stays on for less than a minute before shutting off. Then the cycle doesn't start again till the thermostat calls for heat again which is normal. It's this short cycle after a normal cycle that has me a little confused. Is it normal for the furnace to do that? Could the thermostat be causing it to do that as it is a very old honeywell thermostat. Probably the original that came with the house which is a 1950s house. Another suggestion I was thinking is maybe the fan off switch is starting to go? I had a problem with the fan/ limit switch on another furnace before but the burner and blower/fan was constantly going through short cycles and not just the blower/fan going on off after the end of a cycle.
Any suggestions?
I have a vintage Lennox GH5-75M forced air gas furnace and need a little advice as to whether it is running correctly. I recently cleaned up the furnace from all the dust and cut off some wire that goes from the blower motor to the fixed limit switch to the good part that was exposed because the plastic covering was brittle and flaking off. I re-attached the good part to the limit switch. This is a pretty old furnace but seems to be running ok. It has a separate fixed limit switch and a fan off switch which has temp settings on it. It is set to 120F. I noticed the furnace ran a little off before I cleaned it up. The blower, it seems, would cycle on again about a min after the the furnace finishes a cycle. It would stay on for less than a minute before it shuts off. I'm pretty sure only the blower goes on and not the burner. After the cleaning and wire fix, the furnace ran fine for a couple days but tonight I noticed it did the quick short cycle again.
When it runs fine the thermostat would call for heat and the burners light for about a couple minutes before the blower/fan kicks on. The furnace would run until temp is reached and then the burners would shut off but the blower/fan stays on for another 2-3 mins before shutting off. The cycle repeats when thermostat calls for heat again.
I noticed now, the blower/fan would kick on a min or 2 after a cycle finishes and stays on for less than a minute before shutting off. Then the cycle doesn't start again till the thermostat calls for heat again which is normal. It's this short cycle after a normal cycle that has me a little confused. Is it normal for the furnace to do that? Could the thermostat be causing it to do that as it is a very old honeywell thermostat. Probably the original that came with the house which is a 1950s house. Another suggestion I was thinking is maybe the fan off switch is starting to go? I had a problem with the fan/ limit switch on another furnace before but the burner and blower/fan was constantly going through short cycles and not just the blower/fan going on off after the end of a cycle.
Any suggestions?