# Strange air-conditioner behavior **URL:** \ **Category:** Factual Questions\ **Created:** [May 31, 2006, 2:44pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877 "2006-05-31T14:44:40Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [May 31, 2006, 2:44pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/1 "2006-05-31T14:44:40Z")
My house has central air. Usually, on a hot day like today, it stays on as long as it’s needed, then shuts off. Today though, it stays on for 15 seconds, turns off for about a second, then comes back on again for another 15 seconds. It’s still cooling the house at the correct temperature, so this is more of an annoyance than a problem. So far. So before I call an expensive repair person, I’d like to have some idea of what might be going on, and whether I should call someone right away. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 31, 2006, 2:56pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/2 "2006-05-31T14:56:16Z")
When you say “it”, do you mean it’s the fan that’s cycling on and off, or the compressor? If it’s the fan, I’d say it’s probably your thermostat’s heat anticipator mechanism/circuitry (depending if it’s a mechanical or digital unit). The easiest fix would be to replace the thermostat–something well within the abilities of the average homeowner. If it’s the _compressor_ doing that, it might be more serious, in which case, you’d want a professional to have a look. A compressor should never come back on less than three minutes after shutting off to allow the pressure to equalize, or damage can result. Most modern AC units have a built-in three minute compressor-on delay just for this reason. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [May 31, 2006, 3:07pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/3 "2006-05-31T15:07:17Z")
> [@panache45](#): > > My house has central air. Usually, on a hot day like today, it stays on as long as it’s needed, then shuts off. Today though, it stays on for 15 seconds, turns off for about a second, then comes back on again for another 15 seconds. It’s still cooling the house at the correct temperature, so this is more of an annoyance than a problem. So far. > > So before I call an expensive repair person, I’d like to have some idea of what might be going on, and whether I should call someone right away. If nothing has changed about the house or the weather I’d say you need to have it looked at. Assuming your description of the symptoms is accurate something has abruptly changed about the action of the unit. This is hardly ever a positive indication in a piece of machinery. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [May 31, 2006, 3:32pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/4 "2006-05-31T15:32:32Z")
I’m guessing the compressor’s not actually short-cycling at 15-second intervals. That would rapidly lead to a “locked rotor” condition and trip the circuit breaker. As **Q.E.D.** said, most systems and even the compressors themselves have a roughly three-minute timer before they’ll attempt to re-start to prevent lockup. (A compressor can readily maintain the pressure it creates, but it can not start moving against it, and if unprotected, a compressor can easily overheat and fail.) My guess is a problem in the blower controls. As with everything else in heating and air conditioning, the controls have gotten smarter than the humans, so professional attention is advisable. ---
**Author:** ![handsomeharry](https://avatars.discourse-cdn.com/v4/letter/h/e9c0ed/32.png) [@handsomeharry](https://boards.straightdope.com/u/handsomeharry)\ **Post date:** [June 2, 2006, 1:58pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/5 "2006-06-02T13:58:16Z")
Check the thermostat and see if it requires batteries. I had a similar problem like this and I fixed it with 3 AAs. I think I’ll go into HVAC biz! hh ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [June 2, 2006, 4:30pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/6 "2006-06-02T16:30:37Z")
Once I had that problem…rapid recycling…and discovered I hadn’t removed the vynil cover over the winter. :smack: perhaps your unit is clogged with debris preventing proper air flow? ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [June 2, 2006, 4:36pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/7 "2006-06-02T16:36:00Z")
Check the units air filter. Look for ice on the condenser coils. Check that the water drain isn’t blocked and water backing up in the unit. ---
**Author:** ![hlanelee](https://avatars.discourse-cdn.com/v4/letter/h/3bc359/32.png) [@hlanelee](https://boards.straightdope.com/u/hlanelee)\ **Post date:** [June 2, 2006, 4:40pm UTC](https://boards.straightdope.com/t/strange-air-conditioner-behavior/358877/8 "2006-06-02T16:40:28Z")
It’s probably the capacitor on the inside blower, if the outside unit is still working. Two phase electric motors don’t have the torque to start/run without one. Call an AC guy if you doin’t know anything about it, that would be best. It’s a ten dollar part, but you’ll pay a hundred to get it fixed. :eek: