I have a Amana roof top gas heater/air conditioner. When on heat the gas will light however the fan will never go on. If I use the switch in the thermostat to turn on the fan it comes on and works fine. If I turn the switch off after about 30 seconds the fan turns off again with the gas still on. The schematic for the unit is in the inside door and can no longer be read. I have replaced the robertshaw "igniter control" in the past but at that time the gas solenoid would not operate. I tried to find how the unit determines if the gas has gotten hot enough to start the fan but could find no thermocouple. Is it possible that this is just a timed circuit? Any help would be appreciated.

Thanks John

-- Edit -- The igniter control is a RobertShaw model HS780

Look above the burner for a fan limit switch, it will have a round dial in it with adjustments to bring on the fan.

Look above the burner for a fan limit switch, it will have a round dial in it with adjustments to bring on the fan.

Thanks, There is a circular thing with two thick red wires going into it near the top left of the burner area. I didn't recognize it as something that controlled the fan, I'll check it out.

Thanks again.