In A/C mode, the comppressor turns on , but the fan will not. In heat mode, nothing happens, I'm thinking because the fan needs to run to withdraw the exhaust from the gas. If I turn the fan switch to "on" still have no fan. I have a digital thermostat Any help out there. Thanks in advanced.

Did you try turning the fan to the on position on the thermostat to see if the blower would work? If so and it didn't. You can jumper the R and G circuits on the thermostat to see if the blower runs. If no blower jumper R and G at the blower section. If no blower its time to pull out a voltage meter to find out why or give us a make and model to try and help.

I put it in the "on" position and still nothing. I have about 27 volts from R to ground. When I make it call for heat, I get 27 volts at the G and W terminal. The led flashes like it wants to do something, but nothing happens. I jumped out the R and G and I hear something going on but the fan does not turn on. Thanks

Same problem here - what was the solution?

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It is very possible that you have a problem with the motor. Use a volt meter at the connection where the motor wires conncet to the wires from the circuit board and check across the White wire and the Black wire while the unit is calling for cooling at the thermostat.

Make sure that door switch is compressed.

Also you could tell us what happens when you turn the thermostat to heat, things like does the inducer motor come on and does the hot surfice ignitor glow and does the burners come on.