AC compressor outdoors turning on and off


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Old 05-16-21, 03:04 PM
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AC compressor outdoors turning on and off

Hi. Hope everyone is well and safe.

Turned on ac for first time this season (up here in Southern Ontario). Outside unit is turning on and off repeatedly. Anyone know why this is happening? It's a Carrier Weathermaker Puron system installed circa 2001 and has worked flawlessly every year. Thanks

Got outside to watch and listen to the compressor (hopefully using the right term for it). When it comes on the fan doesn't spin, the unit begins humming and the humming grows louder and louder and then it shuts off abruptly like some kind of switch turns on to protect the unit.
 

Last edited by edee_em; 05-16-21 at 03:12 PM. Reason: Update
  #2  
Old 05-16-21, 03:34 PM
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Take something small in diameter to stick through the grill and see if you can gently get the blades to spin smoothly to check if your fan is locked up or the bearings are going out. This is only one of many causes, but an easy one to check. If it spins easily, then the next step would depend on how comfortable you are on accessing the wiring as there is line voltage inside than can be dangerous.

Without the fan spinning, the compressor can shut off as a safety (until it cools down/internal pressure is reduced and then restarts).

 
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Last edited by Tumble; 05-16-21 at 06:23 PM.
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Old 05-16-21, 04:23 PM
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You can test the fan with the unit powered.
Use a stick and see if a slight nudge starts the fan turning.

With a 20 year old unit it could be a capacitor or a bad fan motor.

Don't allow the compressor to keep cycling on high heat.
Diagnose the problem then shut it off so the compressor can cool off.
 
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Old 05-17-21, 05:32 AM
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Thanks for the tips! I checked the fan just now and it spins freely. However, I have the thermostat on off so it wouldn't call for AC. Power is still going to unit, but should I test the fan movement when it is calling for AC?
 
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Old 05-17-21, 07:12 AM
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As PJ advised, yes. What I would do in order to minimize excess work on the compressor is, pull the disconnect from the unit. Go inside and set the thermostat low so it is calling for cooling. Go outside and reconnect the DC at which time you stated it will start making noise and the fan will not turn. Then using something nudge the fan to start spinning in the correct rotation (it turns so that air is blown outwards). This is to see if the fan capacitor is weak and unable to start the fan up. If nudging it does not start it spinning then you'll have to get inside the unit and do some testing of the components. Minimize the time the compressor is running when doing this test, pull the DC when you are done.

Typical cost of a fan capacitor is less than $20, motor upwards of $300 or more.
 
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Old 05-17-21, 07:19 AM
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I got a bit ahead of myself and removed the capacitor. It is a Rotom 36-40-5-3744 dual oval capacitor. Voltage is dual 370/440V and it has a 40+5MFD rating with +/-5%

I tested it for capacitance and I got 37.1 across C and HERM and 0 across C and F. She's a goner, correct? Also, should I do the other checks or are they needed now that we see 0 for the fan?
 
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Old 05-17-21, 08:33 AM
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Yes, you need to replace it. Note that you don't need that brand, just one that meets those specs. Not familiar enough to recommend a brand for reliability.

Looks like the compressor side of the capacitor was also weak which would tax that start up also. A couple of years ago I installed a hard start kit and it noticeably made a difference (in sound during startup and inrush for the compressor). Circle back to this after you get the unit running w/o it.

While you are in there take a look at the contactor to make sure the contacts are not damaged/pitted/burned excessively. Cheap and easy to replace. Warning! Line voltage present!

After you have addressed these items you can test amp draw if you have and appropriate meter. This can give you an indication of the health of you fan motor.
 
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Old 05-17-21, 09:41 AM
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Take pictures of the wiring.... especially if you change the contactor.
 
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Old 05-17-21, 09:54 AM
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I figured with the original giving me 20 years of service I would stick with the Rotom brand. Made in Canada and a bit more expensive than the chinese brands, but we're worth it!!

Time to clean out the unit. Very surprised to find so much debris in there. After that I will pop in the new capacitor and see where that gets me. Good tip about checking the contactor and I will certainly take a peek (and a picture) at it.
 
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Old 05-18-21, 08:29 AM
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Thanks to your advise and direction we have AC!! Capacitor replacement did the trick. I believe MENSA should be knocking on my door soon, yet my wife remains unimpressed. I chalk it up to her not understanding the amount of knowledge, the number of people and the amount of experience and goodwill that goes into getting such a job completed. Oh well: men are from Mars and women are from Venus and all that...

One thing I did notice is the unit being pretty loud on start up. It is not a quiet unit by any means but I've never stood beside it when it started up in the past. So is a bit of loudness at start up that seems to level off as it goes about its thing, normal? Tumble, you mentioned something about noise at startup.
 

Last edited by edee_em; 05-18-21 at 08:31 AM. Reason: addition
 

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