Carrier 58MXA. Circuit board was recently replaced with aftermarket ICM unit by local HVAC contractor. Since board has been replaced, the fan is not functioning properly. When thermostat ends call for heat, the fan shuts off immediately instead of doing a 90 sec delay. It only does this during probably 1 out of every 4 operation cycles. I have observed the furnace during operation and when it does have fan problem, the status LED turns off for a brief second, like the power to the board has been cut. LED is not flashing any codes. The tech who installed board has already been back once to try to fix problem. He somehow determined that pressure switch was causing problem. Pressure switch was replaced but fan problem is still happening. I guess the real question is what is causing power to board to cut out when call for heat ends. Any ideas?