Hi,

My 58SXA060 furnace wouldn’t turn off the blower after the TSAT stopped calling for heat. Now the blower is constantly ON in HIGH regardless of the TSAT settings. Tried to cycle the power – the blower comes ON in High instantly.

Please let me know if anybody can help!

What brand is your unit?

Make sure your fan on switch is not on at the t-stat

Sounds like you may have a stuck relay

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Originally Posted by Joshdta

what brand is your unit?

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Carrier

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Originally Posted by Joshdta

make sure your fan on switch is not on at the t-stat

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The fan is in AUTO

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Originally Posted by Joshdta

sounds like you may have a stuck relay

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Checked it - no stuck, no power on the coil of the HFR (normally closed)

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Originally Posted by Joshdta

make sure your fan on switch is not on at the t-stat

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Joshdta,

How can I check my TSTAT to know that it does what it supposes to when it calls for heat?

Thanks.

Well when you turn it to heat, do you get hot air or just the blower?

If you heat does not come on it may be a limit switch problem. If your unit over heats the limit will shut off the flame and force the blower to run

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Originally Posted by Joshdta

well when you turn it to heat, do you get hot air or just the blower?

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Just the blower, no heat.
What signal/voltage should I get between which wires when it calls for heat?

28 volts between C and W for heat, sounds like you have a limit switch problem

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Originally Posted by Joshdta

28 volts between C and W for heat, sounds like you have a limit switch problem

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I have 0V between C and W

I also think you either have a bad limit switch, or one of the flame rollout switches may need to be reset.

One quick test for thermostat,, disconnect all wires from thermostat(remember where they go so you can hook them back up correctly) You may also want to disconnect thermostat wires from furnace control board to eliminate the wires as the problem. But, like I said, I agree with josh on this one. If you get no flame, but blower runs constantly, you most likely have a limit issue(either high limit or flame rollout). Let us know if you can locate limits in furnace and we will try to help further. Good luck.

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Originally Posted by serg_e

I have 0V between C and W

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You will only have voltage between c and w when thermostat is calling for heat. You should have voltage between r and c at all times. Please try the wire disconnect test, and let us know if blower shuts off. I doubt it will, but I've been surprised before. Do this first, then we will move on to limits.

0 between w and c? And you have the stat turned up high so the unit will come on?

Are you checking at the unit or at the t-stat? Is the a wire on the c terminal at the stat?

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Originally Posted by mygirlsdad77

I also think you either have a bad limit switch, or one of the flame rollout switches may need to be reset.

One quick test for thermostat,,,, disconnect all wires from thermostat(remember where they go so you can hook them back up correctly) You may also want to disconnect thermostat wires from furnace control board to eliminate the wires as the problem. But, like i said, i agree with josh on this one. If you get no flame, but blower runs constantly, you most likely have a limit issue(either high limit or flame rollout). Let us know if you can locate limits in furnace and we will try to help further. Good luck.

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Disconnected all the TSAT wires from the furnace – the blower (no heat) turned instantly ON as soon as I have powered the unit.

Where should I look for the limit switch/switches?

Good call Josh. There must be a wire between the c on stat, and c on furnace board to get any reading at all from the c on stat. I would suggest doing test at board on furnace if no wire on c at stat.

http://www.furnaceparts.com/eshop/pr.../hh12zb170.jpg

Above the burners and gas valve on the top left or the top right. Also may be a resetable flame role out, a little switch on the side of the burners with a red botton in the middle