Measure the resistance of the temperature sensor with a multimeter. At 77 degrees, you should be able to measure about 5,000 ohms of resistance. If the temperature sensor is faulty, replace it. Check the wire harness connections between the temperature sensor and the control board. If the wire harness is damaged, you can connect it or replace it. You'll need to replace the main electronic control board if the wire harness connections are okay.
Let's Get It Fixed!
HomeX virtual experts will assess your issue (for free!) and can resolve simple problems.