Furnace blower fan works opposite heater element

[DIYer]

The blower fan on my electric forced-air furnace runs when the heater element is not heating, and vice-versa; when the fan is not running the element is heating. It just started doing it today. The system is approximately 15 years old. I have the thermostat set on 71 degrees, but the system continues to run, even when the thermostat is set to "off." It is now 74 degrees, so I had to turn the breaker off.

[hvacwiz]

Your reley that controls fan/elements needs replaced.