# 1979 Bryant Furnace with Fan running nonstop and Central AC not running



## cmgi06801 (5 mo ago)

Hello all,

I have a 1979 Bryant Furnace that is also connected to a central Air Conditioner.

The problem started at the end of the winter when the furnace fan would not turn off at all. I would have to turn the power switch on the side of the furnace off to stop the fan from running. The fan runs immediately once the power switch is turned on again and it doesn't matter if the thermostat is turned off or on calling for heat or cooling. It also didn't matter if the fan is set to Auto or On.
I tried to find out if the fan runs continuously when the unit is calling only for heat or AC too but couldn't. I disconnected the thermostat wires on the control board one by one including GC and even R but still once you turn the power switch on, the fan starts to run continuously. I was told to replace the limit switch but I didn't bother as I wasn't in the house much at the time and it wasn't a big deal to control the fan from the furnace power switch the time I was there. .

I now noticed that the central Air Conditioner unit is not coming on when I have the thermostat calling for Cooling.
After watching a bunch of youtube videos, I did the following:
Replaced the central AC dual capacitor
Confirmed the central AC unit is getting 240V with a voltmeter
Confirmed that the transformer on the furnace unit is getting 110V and has 24V output to the control board
Replaced the furnace control board

Finally, I rigd the Relay Switch in the central AC unit to be On all the time and that made the AC unit run continuously regardless if I have the thermostat calling for cooling or off. Basically, now I control the AC unit from the fuse box and the furnace fan from the power switch...

I ordered and will replace the L250-40F limit switch even though it tested positive for continuity.

What else do you think I should test or do to fix the 2 issues?
TIA


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