I have an 11 year old York furnace that intermittenly blows cold air :confused:. When I turn the power to the unit off and back on, it lights normally and will run fine for a few days. This seems to be occurring at night and from the temperature of the house must be when our setback thermostat returns to daytime temperature. I've replaced the flame sensor and checked voltages but it is still occurring. Any help would be much appreciated!

This is way out from left field Do you have oil,gas or L.P. On a gas line installation I have seen the gas line 'T" fitting without a drip leg and just a 90 elbow to it. In my area its required to have a 6" min. drip leg and cap below the 'T" fitting so condensation/moisture/water doesn't get into the flame. I will keep thinking on this. Did you change the air filter for the air return? Let us know what the fuel is and start from there or if you have a oil burner

This is a natural gas furnace. From the research I've done, I'm beginning to lean towards the pressure sensor, the line that feeds the sensor, or the control panel itself. Hoping to run some tests with my ohmmeter today.

Consider this: you may have a clogged condensate trap or drain tube. The longer recovery cycle it runs in the AM is resulting in condensate flooding.

THANKS! Will check those items this afternoon.