I got a Trane Heat Pump unit that is around 19 years old. For the last few days the relay located in the box located inside the house is been making an horrible clicking sound. I went to the garage and pull guard duty on the relay and when the outside unit calls for emergency heat (gas) due to being too cold outside, the relay is having a hard time making firm contact and it switches on and off very quickly, creating some sparks within the relay. After that a normal click sound is heard and the gas fires up and goes but not for long. I will buy a new relay today and replace it but I'm afraid that I will be addressing the consequence instead of the cause, thanks in advance for all your help. The unit is an XE80 in the inside and a XE1000 outside.