If the fins are cool that says the heaters are not working or the charge is gone. After it has been on for several hours check the outside of the chimney. Is it warm to the touch. If so the heater is working.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles