I have a 2001 Tempstar DC90 Ultra High Efficincy furnace ! The problem is that the fan will not shut off when the desired temp. gets reached?? I have it set for 70 degrees and it lights up heats up gets to 70 degrees flame shuts off but fan keeps going?? I turned off and reset everything multiple times and also made sure my thermostat fan switch was set to auto.
SOMEONE PLEASE HELP W/ SOME ADVICE PLEASSSSSSE!!

Sounds like the blower relay is stuck in the on position from your description. If your furnace has a circuit board this relay is usually located on the board and is not a service replaceable part. You have to buy the circuit board is the relay is the problem. Now some people have tried to replace that relay with one from an electronics store but a real service person will never do that due to liability and lawyers always looking to generate a lawsuit no matter what happened or who caused it.

Sounds like the blower relay is stuck in the on position from your description. If your furnace has a circuit board this relay is usually located on the board and is not a service replaceable part. You have to buy the circuit board is the relay is the problem. Now some people have tried to replace that relay with one from an electronics store but a real service person will never do that due to liability and lawyers always looking to generate a lawsuit no matter what happened or who caused it.

hvac1000 would you still that would be the problem even if occasionally it shuts off and works once in awhile?

There are many different possibilities but the blower relay always comes to mind first since I have seen that many times before.

You could have a shorted green wire at the thermostat all the way down to the furnace. The green wire or G terminal controls the blower in the A/C mode but if shorted could cause the blower to run no matter what you set the thermostat at. just for the heck of it disconnect the G= Green wire at the low voltage terminal strip in the furnace or low voltage thermostat wires that feed the furnace and see if the blower still has problems. If it works OK after the G wire disconnect then you have a wiring or thermostat problem.

Now if you changed the thermostat lately and did not state that in your first post that could be the problem. Try the G wire removal and post back. NOTE leave all the other wires alone and kill the power before removal and do not allow the wire to touch anything else during the test.

Only a black and white wire that runs from the thermastat to furnace