SERVICE CALL 6

A customer calls on a very cold day and explains that the gas furnace just shut off and the house is getting cold. The system has a printed circuit board, Figure 15.37.

The technician arrives and checks the room thermostat. It is set at 73°F and the house temperature is 65°F. The thermostat is calling for heat. The fan is running, but there is no heat.

The technician removes the front door to the furnace, which stops the furnace fan because of the door switch (see 9G at the top of the diagram). The technician tapes down the door switch so he can troubleshoot the circuit.

The technician places one meter lead on SEC-2 (the common side of the circuit) and the other on SEC-1 and finds that there is 24 V. The meter lead on SEC-1 is then moved to the R terminal, and 24 V is found there. The lead is then moved to GH, where the signal from the room thermostat passes power to the circuit board, and there is power.

The technician then removes the lead from GH and places it on the GAS-1 terminal, where the technician finds 24 V.

What is the problem and the recommended solution?