Hi, Just found your site today-yipee! I have a problem with my Coleman-Evcon furnace (it has had A/C added)-just bought the house this year, but previous occupants said all was working before. When I turn on the heat on the thermostat, I get a code 3 readout, "Centrifugal Swithch Open"; I had seen somewhere someone said they disconnected the Centrifugal Motor and moved the motor around manually and that it overrode the code for a season(?), strange, but it didn't work initially, after going back to the unit and flipping the switch off and on several times I finally got it to turn on the Centrifugal, then it gave me a hard time lighting, but, got past that after about an hour, then it was in heat up mode and I was out checking all of the vents hoping to have hot air soon when the fire/heat alarm went off in the utility room (furnace installed there), and I found the heat exchanger very hot and a code 4 "Limit cycling". Since then I haven't been able to get the Centrifugal to turn on again still getting a switch open contition. Model NR DGAT056BDD, ser nr. 950860279 .

Time to call for service before you blow it up.

Sounds like you have a bad inducer blower wheel. I agree with hvac100 its time to call a tech before you do more damage.