Magic Chef L6A112C16-1 Forced Air Blower Question
#1
08-30-15, 08:44 AM
Magic Chef L6A112C16-1 Forced Air Blower Question
We are on A/C now so I'm posting this question here.
The blower for the forced air became noisy over time and I replaced the bearing, then had motor problems and I also replaced the motor.
The belt fell off recently and I noticed that the drive pulley on the motor has one face on a threaded portion of the hub so that the width can be adjusted, there is also a lock screw to hold the position once it is adjusted. The plates are much larger than the hub so it seems as if this pulley is designed to allow speed adjustment by forcing the belt to ride higher or lower on the pulley.
The drive pulley is about 3" but can be adjusted down to 2" maybe a bit less, and the other pulley is about 5" in diameter. How do I know the correct setting for the drive pulley, or the correct ratio for the pulleys?
Is this intended to provide control over the amount of airflow?
The blower for the forced air became noisy over time and I replaced the bearing, then had motor problems and I also replaced the motor.
The belt fell off recently and I noticed that the drive pulley on the motor has one face on a threaded portion of the hub so that the width can be adjusted, there is also a lock screw to hold the position once it is adjusted. The plates are much larger than the hub so it seems as if this pulley is designed to allow speed adjustment by forcing the belt to ride higher or lower on the pulley.
The drive pulley is about 3" but can be adjusted down to 2" maybe a bit less, and the other pulley is about 5" in diameter. How do I know the correct setting for the drive pulley, or the correct ratio for the pulleys?
Is this intended to provide control over the amount of airflow?
#2
08-30-15, 09:34 AM
Forum Topic Moderator
I usually shoot for a 2/3 ratio and prefer the running amperage to be 10% under the motor FLA of the motor.
#3
08-30-15, 09:38 AM
Member
Yes, the adjustable pulley is meant to allow for changing the drive ratio (motor speed to blower speed) to adjust the amount of airflow. When in heating mode, you want to adjust the blower speed so that the stack temperature holds relatively constant, not going up or down any appreciable amount after it's reached its steady-state condition.
If the blower speed is too low, the stack temperature will continue to rise and eventually reach the high limit temperature and shutdown the furnace. If the blower speed is too high, the stack temperature will fall until it reaches the lower temperature limit and the furnace will continue to run (burners on), but the blower will shut off, then when the stack temperature rises the blower will turn back on again, resulting in the blower cycling on/off/on....
If the blower speed is too low, the stack temperature will continue to rise and eventually reach the high limit temperature and shutdown the furnace. If the blower speed is too high, the stack temperature will fall until it reaches the lower temperature limit and the furnace will continue to run (burners on), but the blower will shut off, then when the stack temperature rises the blower will turn back on again, resulting in the blower cycling on/off/on....
#4
10-26-15, 08:42 PM
Hi Bob, Thanks for that detailed reply. This is a two zone system and the furnace does hit the limit switch when only one zone is calling for heat. Do I read the stack temp with both zones calling?
#5
10-26-15, 11:52 PM
Group Moderator
You need the furnace to run with one or both zones calling for heat without hitting the high limit.
#6
10-27-15, 05:39 AM
Member
As Pete stated, the furnace should never hit the high limit. You should raise the blower speed (make motor pulley larger) until the stack temperature doesn't hit the high limit (one zone calling for heat). After doing this, check operation with both zones calling for heat. Hopefully, the blower won't cycle on/off/on because of the blower speed being too high.
I'm wondering if the airflow is being restricted too much when only a single zone is calling for heat. If the system doesn't hit the high limit with both zones calling for heat, but does with only one, it suggests that there is a significant difference in airflow through the system between one or both zones enabled. Have you noticed whether it makes a difference which zone is calling for heat whether it hits the high limit?
I'm wondering if the airflow is being restricted too much when only a single zone is calling for heat. If the system doesn't hit the high limit with both zones calling for heat, but does with only one, it suggests that there is a significant difference in airflow through the system between one or both zones enabled. Have you noticed whether it makes a difference which zone is calling for heat whether it hits the high limit?
#7
10-27-15, 10:18 AM
Group Moderator
Air zoning systems can be touchy. Sometimes a bypass damper is not set correctly or isn't working.
