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Old 01-17-2012, 06:56 PM   #1
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Day and night Furnace.Blower clicks on and off.


Hello i have a Day n nite. Furnace i am working on.Its 1980s. I put the thermostat to cal. The blower comes on. Then it fades and shuts down. Innitially i was convinced it was the blower itself. I have 3 wires coming off the blower. Black white and red. white is common. I checked for amp read around each wire. I get 6 amps. On two of the 3 wires. Can you help me.?

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Old 01-17-2012, 07:18 PM   #2
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Day and night Furnace.Blower clicks on and off.


I'd be checking the run capaciter( or changing it as they are cheap) and testing whether the motor is getting a constant 120V when its shutting on & off.


Last edited by how; 01-17-2012 at 07:20 PM.
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Old 01-17-2012, 07:47 PM   #3
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Day and night Furnace.Blower clicks on and off.


if you have AC put the faan to ON if it runs right then its the heating side of the unit that is bouncing the fan.note supply fan for LO/MED LO heating is controlled from the furnace not the stat as in cooling HI speed
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Old 01-17-2012, 07:49 PM   #4
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Day and night Furnace.Blower clicks on and off.


Thank you . The capacitor is a 5 MFD. 370V. i got a reading of jus over 3 MFDs. i was had one on the truck and i installed it. still have a lagging blower then clicks off.I checked volts like you said for 120. my reading is under 55V. What is going on here? Can yu help?
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Old 01-17-2012, 09:35 PM   #5
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Day and night Furnace.Blower clicks on and off.


What are you measuring to get 55V. Are you measuring it between the Black and the white or the red and the white? Was the motor running when you measured this? Do you get 120V between one wire and the white and 55V between the other and the white?
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Old 01-18-2012, 09:12 PM   #6
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Day and night Furnace.Blower clicks on and off.


I get 55v. from White to black. I checked the Power coming into the circuit board. I get 119V. L1 & L2. I have 24 v. reading at the circuit board. Secondary 1 & 2. when i bypass the 24 V. wires R & w. I get nothing. I get no volts coming from r & w. at the airhandler.I checkd the door switch thinking partial voltage may occur here. I bypassed this door switch to take it out of the loop . still no cant get the system to work. I noticed it has an electric filter at the bottom. Gota be careful of this. Theres a step up transformer that keeps this thing working. Any other tips? Thanks for your input on this. Its not an easy fix for me.
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Old 01-18-2012, 09:56 PM   #7
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Day and night Furnace.Blower clicks on and off.


Did your furnace fan initially run all the time on a low speed and then rise to a higher speed when the furnace was heating?
Just wondering with your two motor speed taps if you have a 2 speed set up for heating or if one is for heating and the other one is for cooling?

I would have thought that the red line to your motor would have been for heating and the black line would be reserved for A/C or a summer fan. If you follow those two motor lines (black & red) back to the board the places they plug into the board will probably be marked. These connection points on the board ( with the black & red wire removed and isolated) is where I would be checking for 120V when the board is calling for the blower fan to operate.

It will help point to a board relay issue or a motor problem.

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