From time to time, I will go on a service call. Let me share with you what I ran into the other day. A friend called me to take a look at his AC system that was not working. It was a simple repair, bad capacitor, but to check and replace the capacitor power must be disabled.
I disable the power to the AC unit all the time, and so will you. Most systems have an air conditioning service disconnect box. It is mounted outside near the condenser and inside near the air handler. It is designed so that you’re able to disable power to the unit you are working on without locating, tagging, and locking out the circuit breaker. Power is disabled by simply pulling out the bus bar using the T- handle. Once removed you can safely work on the equipment knowing that the power is disabled… Right?
Well, I always check to make sure the power was disabled to the unit and guess what? I measured 250 volts with the disconnect removed! Good thing I practice what I preach. NEVER not EVER should you assume that by removing the bus bar that the power is disabled.
I pull out the bus bar 1,000 times (and so will you) on 1,000 different service calls and have the power disabled to the unit without a hitch. But… on the 1,001 time, when you assume that the power is disconnected after you pull out the bus bar, and you decide not to check and double check the voltage, this is what you’ll find, the same thing I did.
Believe me, this will be what you run into on your 1,001 time or maybe your 10,001 time, but it will happen!
Don’t assume, don’t become complacent. Always check and double check the circuit you’re working. HVAC SAFETY, SAFETY, SAFETY!
by Ron Walker