Any Heating & A/C worker worth their weight in gold should make sure the power is off, prior to working on any cooling system or furnace. Having the right tools, skill, and right parts to fix any cooling system or furnace is important. However, you are also going to need one other thing – the electricity needs to be off, for whatever appliance you are particularly working on! This is especially true for Heating & A/C units, as they rely solely on electricity to function properly (unless they use gas as a fuel). Even houses that have gas-controlled furnaces as well as cooling systems would have the power turned off first! At the least, getting shocked could leave your hand burned from the current of electricity. Worst case scenario, your heart could stop! Never make the mistake of thinking that the breaker panel has everything marked correctly, and if you turn off the breaker that is supposed to be for the furnace or cooling system, always make sure to check it with a multimeter before taking the unit apart. You can never be too cautious about this kind of thing! They also sell testers that beep, any time it finds an electrical current near it. These are costly resources for working on Heating & A/C appliances, but worth it! I remember when I had a friend that worked as a Heating & A/C technician. He was always confident around Heating & A/C units, and knowing if the power was cut off. One day, he was wrong – and he paid the price with his life! Don’t take any risks; make sure the power is off!