Hello....I fired up my ~ 10 year old furnace just today for the first time this cold season and got consistent cold air blowing out the vents. The control panel is flashing 4 times and then a pause. I found a pdf form that says this about the error message:
"4 RED FLASHES: This indicates that a primary or auxiliary limit switch has opened its normally closed contacts. The control will operate the supply air blower and inducer. This condition may be caused by: dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate or faulty blower motor. Also, this fault code could be caused by a blown fuse located on the control board."
I checked the fuse and its good. I checked the Primary and auxiliary contacts with no power on the furnace and continuity was there. I assume the contact breaks when the system starts? Filter is new. Blower seems good. Any help on this would be great. Model g8t08012dna11a serial wdlm003595
If it is a white rodgers control module, go to their site and punch in the model number. They have some good troubleshooting guides complete with flow charts. Its sometimes better than calling their support, which I'm sad to say can be hit or miss.