Hi there, my a/c worked fine until a few days ago but now here is my problem... the blower on my furnace (5yr old Keeprite) works fine when the thermostat is set to 'ON' but when I turn it to 'AUTO' it shuts down. My a/c works but the blower will not come on when it starts up. Any ideas?

Possible bad tstat
Possible broken tstat wire somewhere

Have you got a meter to check voltage on wires?

Till you figure it out ,you can run it,, fan on and air on should cool but the indoor fan just won`t stop running, which is how some people like to do it anyway

I replaced the tstat. Same problem. Any time the air goes on the blower shuts down so I can't use my air at all or the lines freeze up. I tested the voltage and when the blower is on everything seems fine and same with the a/c wires. The problem is when the air is on there is no power going to the blower at all.

The furnace runs off a circuit board and the blower is 4 speed.

Is it possible it is a faulty circuit board?

If the fan relay is located on the circuit board then you probably need a new board.