I have a coleman 7966-856 mobile home furnace. burner comes on, blower comes on about 5 min later then shuts off after about 30 seconds and flame stays on. changed fan switch low limit switch and aux switch. part of scematic is missing. Blower runs fine in a/c mode. furnace and a/c are controlled by two seperate thermostats. a/c stat is in off during this occurance. can't figure out what it could be
remove the heating stat off the subbase and jump R to W lets hear wht happens so that cooling stat has no heat setting or effects the heating call...note your fan cycle in heat comes from a thermal disc or relay on a solid state board so it's either or we'll see
Usually those furnaces use a temp on temp off fan control. It looks like a round limit switch but it closes on rise energizing blower. It shouldn't take so long to energize and too quick on shut down. Sounds like a bad fan control, either wrong if it had been replaced or weak they do go bad.