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I have always been told that one should wait (at least) 3 minutes after turning on an air-conditioner before turning it off, and wait 3 minutes after turning off an air-conditioner before turning it back on. I have also heard that not doing so breaks the air-conditioner.

Does this have any truth to it?

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    It's half true. As others have posted below, starting a compressor under load is not a good thing. There's no such issue with turning it off after a short run, though. – Loren Pechtel Jun 19 '14 at 18:37
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My first thought was that this was certainly a myth, but it seems like I was quite wrong - this appears to be true (or at the very least, it's corroborated/perpetuated by a lot of sources).

From Frigidaire (page five):

Please always wait 3 minutes when turning unit off then on again, and when changing from cool to fan and back to cool. This prevents compressor from overheating & possible circuit breaker tripping.

From Amana (page 17):

If you turn off the air conditioner, wait at least 3 minutes before turning it back on. This prevents the air conditioner from blowing a fuse or tripping a circuit breaker.

And page 18:

If the air conditioner is off and then turned on while set to a COOL setting, or if it is turned from a fan setting to a COOL setting, it may take approximately 3 minutes for the compressor to start and cooling to begin.

From Whirlpool:

If you turn off the air conditioner, wait at least three minutes before turning it back on. This helps to avoid the air conditioner blowing a fuse or tripping a circuit breaker.

From Haier (page nine):

Also when you shut off the air conditioner wait for 3 minutes before turning it on again. This is the compressor cycle time.

And from Topline HVAC, an HVAC company out of Chicago (which has one of the more irritating websites I've come across in a while, do check it out, including the home page):

When turning your air conditioner off, try to wait 3 to 5 minutes to allow the refrigerant pressure to equalize before turning your air conditioner back on. It gets very hard on your compressor, when it tries to start under high pressure, if you do not wait for your system pressures to equalize.

There are also about a million other results from Google. It's entirely possible this is all a super-safety-precaution, like a warning that peanut butter contains peanuts, and you might never experience any problems at all. But it's easy to be better safe than sorry here and let the compressor units stabilize.

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    Ah, I mis read the question. In this case it's always easier to start a motor that has no load than to start a motor under load. In order to save money they use inexpensive motors that aren't rated to start under the full compression load. Once the motor is running it has no problem maintaining the power reqred to compress the refrigerant. Startup is an altogether different matter though. – Adam Davis Jun 18 '11 at 1:36
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    @Adam Davis: Very good addition. – erekalper Jun 18 '11 at 15:19
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    When I read the question, my first thought was: If it's so, then it would be written in the manual, no? – Andy Jun 20 '11 at 17:08
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Yes. The compressor motor will stall if you switch it off and on too quickly, resulting in an overload which can trip the circuit breaker and possibly overheat and damage the motor.

A technical explanation of why this happens can be found at Electrical Engineering Stack Exchange: Why do refrigeration compressors stall when switched off and on quickly? (disclosure: I asked this question) To quote "horta" there:

The compressor compresses coolant on one side of a closed loop. If you shut off the compressor, you still have the load side of the closed loop full of pressurized coolant. That pressurized coolant makes it much more difficult to start the motor. A motor starting at 0 RPMs will want to draw large amounts of current. With an added load to the motor (pressurized coolant) the motor will draw excessive current and won't turn over.

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protected by Oddthinking Aug 6 '14 at 22:13

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