All seems to be OK, the heater and pot are within specs. Voltage to the heater ranges from about 111 ("ex low" temp) to 2about 26 volts (max temp).
But the thing seems to have no effect on the exit air temperature. With an electrical thermometer in the duct about 5 feet from the outle, temperature cycles between about 150 deg and 107 deg regardless of the setting.
The state is marked 150 deg and 20 deg (which I take to be the differential).
Any advice would be appreciated.