Blower constantly runs on furnace


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Old 04-29-12, 12:02 PM
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Blower constantly runs on furnace

I'm new here so sorry if this has been addressed before. I have a 1987 York furnace. I recently installed a new thermostat, but acccidentally crossed two wires and blew the transformer. I fixed the wiring on the thermostat and replaced the transformer. Now the blower runs constantly unless you pull the panel off the front to kill the power. Could blowing the transformer have burnt out the fan limit control? How could I check this? Any ideas or suggestions would be greatly appreciated.
 
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Old 04-29-12, 01:59 PM
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On the fan limit control, there might be a white peg - pull it out.

Check for a short between R and G at the thermostat and furnace. (if G is connected)
 
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Old 05-06-12, 11:56 AM
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The peg on the fan limit control is missing and the G isn't connected. One thing I tried was manually advancing and decreasing the points on the fan limit control, but it made no difference. The fan just kept running.
 
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Old 05-06-12, 08:32 PM
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1. With the power off, open the fan/limit switch.

2. There should be three or four wires connected.

3. One side is labelled fan, the other should be labelled limit.

4. On the fan side, disconnect the wire which leads to the blower motor (trace the wires) and tape it off.

5. Restore power.

If the fan doesn't run continuously any more, the fan limit switch is bad. If you choose to replace it, have your supplier cross reference the model number (there are different lengths). If there are four wires connected to it, be sure to remove or cut the low voltage jumper, otherwise the low voltage components will get fried as soon as the t-stat calls for heat

If the fan still operates, there's another problem with the furnace.

Some older belt driven blowers may run at a low continuous speed when there's no call for heat.

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It's a good idea to wire an inline fuse into the low voltage circuit to prevent the transformer from getting damaged. (2-3 amps, 30V+ should do it)
 
 

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