Is my problem electrical or mental?
June 18, 2014 10:57 PM   Subscribe

When my central air turns on or off, I hear a loud popping sound coming from the thermostat area. I have replaced the thermostat and still hear it. I'm sure that I have always heard it and that other ac's have made that noise but, for the past few months, it seems to have gotten louder and it wakes me up throughout the night. It is driving me crazy. Is your thermostat that loud? Could this be an electrical issue?

I started noticing it at the beginning of a very stressful period when I also started having exploding head syndrome (google it, it's nifty) and now I'm wondering if it is just stress that is making me ultra sensitive to a noise that was already there or if it has actually gotten worse. What are your thoughts? Have any of you had this problem?
posted by myselfasme to Home & Garden (6 answers total)
Air conditioners do two things. The compresser exchanges the heat from inside to outside [like a refrigerator but in reverse] and a fan passes that exchange along. There are sometimes two motors. Some AC units shut off the compressor while still allowing the fan to pass air over the coils because there was an "investment" in cooling and the heat exchanger still has something to yield. My AC sometimes accelerates the fan at the end of the cycle - depending on what I have no idea.

To answer your question more directly, "Is my problem electrical or mental?" It's neither. Definitely not mental, maybe mechanical. There might be a solenoid [a really simple thing that either goes out or in] that engages a motor that powers both the compressor and the fan and that is what you are hearing.

Call the local AC people [more than one for sure, and ask for a bid from each. Don't be shy here, this is a normal part of the process] The old guy or gal with really clean clothes is normally the one to believe.

memail me if you need moral or technical support.
posted by vapidave at 12:18 AM on June 19, 2014

The thermostat probably has relays that you can hear click just before the a/c or heat comes on.
posted by TheAdamist at 3:05 AM on June 19, 2014

A thermostat should not make enough noise that it can wake you up. Something is wrong. It is more likely mechanical than electrical. You need an HVAC guy, not an electrician.
posted by Flood at 4:03 AM on June 19, 2014

My old-school, round, non-digital thermostat clicks when the heat is about to come on. I can hear it from any of the rooms that adjoin the room with the thermostat. I think that's fairly normal behavior, but the sound wouldn't wake me. My votes are for your thermostat being normal-but-weirdly-loud, or that stress has got you sleeping less soundly.
posted by donnagirl at 4:29 AM on June 19, 2014 [2 favorites]

My new-school, digital, programmable thermostats also click loudly when they turn the AC or heat on or off. There's also a click when the Super Expensive Heat ("AUX HEAT ON") turns on. I suspect it's relays in the thermostat, since the thermostat's powered by 2 AA batteries and the A/C's on 240V. Whenever you have a DC Thing controlling an AC Thing, that control needs to be done through a relay.

The sound is not loud enough to wake me, but I sleep like the dead, so who knows. In my opinion, the sound of the actual A/C or heat fans is louder. I'd describe the sound as a click rather than a pop.

Call your local HVAC service technician. They'll probably be able to tell you what it is over the phone without having to come to your house. If you have an annual maintenance contract (you DO have an annual maintenance contract, don't you?), and they do need to come out, it should be a free call.
posted by tckma at 8:31 AM on June 19, 2014

Could this be an electrical issue?

If it only popped when it turned off, or if the sound was much louder then, I would guess that the power supply to the thermostat was wired up backward.

The contacts in the thermostat need to be between the hot side of the power and the device the thermostat controls--the relay, or solenoid, or motor, etc.--because the magnetic field in the relay (etc.) collapses back through its coils when the thermostat turns off, and that will generate enough voltage to arc across the contacts to ground as they open if the contacts are between the relay and ground instead of between the hot side and relay as they should be.

Such arcing generates a loud popping sound, and will destroy a set of contacts in pretty short order.
posted by jamjam at 9:08 AM on June 19, 2014

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