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Hello. I have a 15 year old Evcon DGAM075BDD furnace with A/C. The circuit board took a lighting hit. I replaced the circuit board and transformer with new. Now, at any thermostat setting, including "off", blower fan will come on for 3-4 minutes, then off 30 seconds, then on 3-4 minutes, etc. Different thermostat settings (combinations of Heat-Off-Cool; Fan-Auto-On) have no effect on blower motor cycling - the blower motor still cycles as described. Example: heat does cycle OK but when at temp and burner kicks off, blower fan will continue to cycle as described: on for 3-4 minutes, off for 30 seconds, etc. I checked the wiring of new circuit board and transformer and all wiring seems OK and as per original board connections. Any thoughts? (I appreciate any ideas. Thank you.) Frank

Three more comments and a single question (please). (1) The original circuit board was the 7990-319P. The new replacement is also the 7990-319P (purchased from this site), not the 7990-320P. (2) Now when the t-stat calls for heat, the blower, from a constant-running-cycling state as described, STOPS UNTIL the heat exchanger is up to heat, then the fan comes on, all as per normal; when the t-stat is up to temp, gas shuts off normally, fan continues for a bit, then stops in a normal post-heat blower-stop; then abnormally the blower starts up on it's own with no heat-call and begins the permanent start/stop "cycling" described. The only way to stop this is to shut off power to the entire furnace. (3) Since for my Coleman/Evcon model (1995) there appears to be no separate fan control switch, or sequencer switch, such that those functions appear to be all part of the 7990-319P circuit board, then the suspect part is "surprise" the 7990-319P circuit board. Thanks for any ideas you may have. I appreciate it.

When the fan is doing the on-off stuff, put a meter across your limit switches and see if they are opening and closing at the same time.

Mark

Hi Mark,

Thanks for the help. Since writing the above, I've replaced with new parts: (1) the lower limit switch, (2) upper limit switch, (3) booster assembly, (4) thermostat. I also cleaned the remote flame sensor. The problem still exists with the exact same behavior. I also disconnected the lower limit switch, and the problem still exists with the exact same behavior. So I think the problem is the board. Any thoughts? (Thank you again.)

Sounds like a defective board.

Mark

'Sounds like you're right. It was a defective board. Meaning: the 7990-319P factory-new replacement board was DEFECTIVE, such that your moderator Robert was correct in his related post that the 7990-319P is inherently defective and that the upgraded board, the 7990-320P, fixes the problem. Moreover, I did NOT NEED all those other replacement parts; I only needed to replace the new but defective 7990-319P board with the upgraded 7990-320P board and all the problems were solved.

Ive got the same problem with my coleman DAT075BDF Already had one board repaired by them and bought a new one too. Problem has returned how about you?