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I have an air conditioner that is probably 15 years old now. The problem is when I turn it on after it has been off for a long period of time (several hours) it takes a long time for the outdoor unit (compressor?) to start running.

The outdoor unit has a large fan in the middle with cooling coils around the perimeter and cooling fins. It had been running just fine up until three summers ago. Two winters ago, my heater went out and I had it replaced. The following summer (last summer) I went to turn on the air conditioner for the first time and it took so long (30 minutes) to come on that I thought it was broken or not wired up or a fuse blew. I checked all the obvious things like the set temp was below the room temp. (72 < 90). The wall unit has a red light that glows when either the heater or air conditioner unit is operating. I figured the heating & cooling guys forgot to hook something up. Having a bit of electrical know-how, I went and checked the outside fuses and other things and could see the outdoor unit had voltage going to the outdoor unit.

Just today, first time turning on the air conditioner for the year and same behavior. Here is the interesting thing though. Once the unit kicks on, it cycles normally. I can hear a small click (relay closing) on the inside thermostat unit each time the termostat cycles on/off. I can then hear the outside unit kick on within a few seconds of hearing that click (normal).

On mild days, I turn the air conditioner off and it may be off for a day or two but then turning it on for the first time, I can hear the thermostat click but the outdoor unit takes 30 minutes on average to come on for the first time.

I don't have a schematic for the unit but I can't imagine an outdoor relay taking that long to engage if it's a relay problem. Also the outdoor unit has this blanket around the motor. I tried removing it when this problem first began but the unit seems sealed up.

The guys that put in my new furnace insist they did nothing that would have caused this but want $85 to come look at it.

Anyone recognize this behavior?

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  • When did you last get it serviced? If it's been a while, might be worth the $85...
    – Bryce
    Jun 22, 2012 at 8:00

4 Answers 4

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There is probably an old capacitor in the electronics which dried out over the time and now takes a long time to gain the necessary power load. If you are familiar with electronics you can check yourself for capacitors which looks bloated or otherwise funny and replace them.

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    WARNING: Capacitors can be dangerous, and can injury/kill you if not handled properly. Do not attempt to work with capacitors, or on circuits that contain capacitors unless you know what you are doing.
    – Tester101
    May 29, 2012 at 15:55
  • They need to be discharged under an appropriate load. Not a DIY project
    – Chris Cudmore
    Jul 29, 2012 at 1:39
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    Yes, i wound up replacing all two capacitors and relay and problem seems resolved. I also learned previous owner or AC person installed a hard start capacitor which I removed when I installed the two new ones and relay. Seems good as new now. I made this post in 2012 and sort of lived with this problem until 2018... then sold the house in 2019. One of the old capacitors was highly corroded like rain water maybe pooling on top of it maybe shorting the contacts. When i installed the new capacitors, I was sure to install with lead wires facing down instead of up as they were.
    – Eric
    Aug 15, 2020 at 15:28
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I know that when a capacitor fails to start up it can cause the compressor to overheat and it will simply be slow to start. Therefore switch off the power, and after it gets cool, replace your capacitor for proper operation. And if you are in a hurry, you could pour some fresh water to the compressor to cool it.

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  • since when is pouring cold water on a hot piece of equipment to cool it a good idea? I'm thinking engines here, but I imagine the concept applies to compressors to some degree as well.
    – stu
    Jun 6, 2017 at 13:38
  • @stu - On a sealed unit that's the equivalent of pouring water on your hood. Rain doesn't bother cars or condensers.
    – Mazura
    Jun 1, 2018 at 19:50
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If your outside unit isnt cycling on and you have line voltage coming in to L1 and L2 first thing I would check is the contactor you say it does come on.If its cooling when it comes on the your condensor fan and compressor are working fine.

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Likely a relay timed to close (tc) and create a delay. Situated in the furnace panel to protect the compressor

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here.
    – Daniel Griscom
    Aug 14, 2020 at 14:50
  • Do note that you answered an 8 year old question....
    – FreeMan
    Aug 14, 2020 at 17:17
  • @FreeMan -- there is no rule against necromancy in Stackland :)
    – ThreePhaseEel
    Aug 14, 2020 at 23:02
  • That is quite true, @ThreePhaseEel, however, considering this one has an accepted answer (though it seems it was only accepted a few minutes ago...). TBF, OP commented on the now accepted answer that he got this fixed just within the last year or so.
    – FreeMan
    Aug 15, 2020 at 15:40

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