furnace blower turning on and off - http://www.hvacmechanic.com/ Forums
Original message
| john_34
 |  "furnace blower turning on and off"
, posted Sun 9 Nov 09:16  
I have a furnace blower in the attic for the second floor that is fed by a Burnham boiler (model P-206A-WNI)in the basement. I have a Bryant furnace blower in the basement for the first floor. The blower in the attic cycles on and off for about 15 to 20 seconds about 4 to 5 time an hour with no call for heat. When there is a call for heat it works just fine. I have a Honeywell mpls min 55422 ignition board and a Honeywell thermostat set to 200, both are inside the boiler cover. There is a Honeywell aqustat type L6007A, L6008A set at 175 next to the Bryant furnace blower. I believe that the aquastat is the limit switch for the Bryant. I can't find the limit switch for the blower in the attic though. Could it be the one inside the boiler cover?
Any help would be greatly appreciated. john.
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Replies:
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| Xenos
Webmaster 
| "Re(1):furnace blower turning on and off" , posted Sun 9 Nov 09:31
If it is a thermostat causing this in the off cycle I am wondering how the water flow operates. Does the water cycle on and off on a flow valve through the unit. If this valve was leaking water through it, this would warm up the air handler but since the heat load is small the fan would cool it off right away. Hence the cycling.
Xenos.
The best way to escape a problem is to solve it.
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| Xenos
Webmaster
| "Re(1):furnace blower turning on and off" , posted Sun 9 Nov 09:26
If I understand this correctly Your furnace in the attic is an air handler with a Hot water coil in it. Is it just an air handler or does it also have back up heating?. IF the fan is acting as you mention my first though is there is as you mentioned a thermostat in the unit starting the fan when the unit gets too warm and since there s no demand it would cool instantly and shut down. A second thought is the fan is electronically controlled and this board is malfunctioning.
Xenos.
The best way to escape a problem is to solve it.
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| | john_34
| "Re(2):furnace blower turning on and off" , posted Sun 9 Nov 10:00
When the blower is cycling on and off there is no hot water flow to the blower. When the Honeywell (T87F) calls for heat then the hot water flows. I did take a side panel off the blower unit and I could not see thermostat inside, just the motor, fan and coils. There is a box on top of the unit where the power comes in along with two other cables (from the boiler and thermostat?) that tie into a switch. I was hoping for a limit switch that I could adjust for that blower.
thanks john.
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