Air conditioners need to be de-bugged too!

This past Saturday, my Air conditioner, only 2 years old or so began making a loud buzzing noise when it came on in the morning.  Andrea woke up early, and was trying to be quiet, as not to wake me, but I ended up waking up anyways when the air conditioner started up and was making a loud buzzing noise similar to a game show buzzer.

I was worried, as it sounded expensive.   Well, it’s got a warranty on it, but I may still need to pay for the service visit.  Luckily, it was still cranking out cold air, so I was thinking it maybe not all that bad.    I decided to check it out myself.  I put on my clothes and went outside to the outdoor unit.  Using my ears, I was able to source the problem down to the electrical enclosure on the side of the unit.


I switched the unit off with the thermostat and began to investigate.  I found that if I pushed the button on the contractor relay, the unit would start up and hum just as quietly as it typically would.  This is a big relief to discover…no expensive motors or other parts were the cause of the problem.  Check out the video below to see for yourself:

My buzzy, buggy AC unit

What does the contactor relay do?   Simple actually.  The thermostat inside the house operates at a low voltage,  24 volts.  The air conditioner however works at a high voltage, 240 volts…10 times higher.  Instead of running the massive high voltage wires through the house to the thermostat, thin, low-voltage wire is run instead.  The contractor relay is simply a switch that receives that low voltage signal from the thermostat, and uses it to turn on the high voltage that runs the compressor.

I obtained a new contactor and replaced it easily.  Replacing the part was an easy 10 minute job at best:


After replacing the unit, I decided to investigate the old one, and see what made it fail.  I had heard this particular contractor relay was a failure-prone model, so I wanted to find out what made it troublesome, as I am curious in that way.  Well, once I disassembled it, I found that the failure was not actually the fault of the design, but it had a big….literally…in it!


The piece you see here moves when electricity flows through the coil above my finger.  The buzzing was because it wasn’t making complete contact with the flattened bug sitting between it, and the coil inside the housing!  This issue reminds me of the first computer, and where the term “bug” became associated with computers, and it was found…yep, in a relay!    ..I wonder why bugs are attracted to electrical relays?!?!

computer bug

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