A/C condenser doesn't turn on at night


  #1  
Old 07-05-12, 06:56 AM
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A/C condenser doesn't turn on at night

I have a very specific problem with my upstairs A/C unit. It is a ~12 yr old York HLRA048S06D 4-ton 10 seer (?) unit. It has been blowing nice, crisp cool air in the 100+ temps we've been having here in TX...except at night before bed.

I usually set it to 85 during the day, down to 78 at 4:30pm and then 76 at 10:30pm when we go to bed. It works very well in cooling the upstairs down to the set temperatures, but lately the condenser unit shuts off at night, around 8:30-9ish. The interior fan was blowing room temp/warm air, and we've had to go to sleep uncomfortably in low 80s temps. I notice when I get up at 6:30am, the condenser has turned on sometime during the night, and it is 76 deg once again. This started happening last week, was sporadic at first at night but now has been happening for the last 3 nights straight.

I had an A/C technician come out to check on it in the afternoon, but as it was blowing cold air he could not diagnose anything wrong. The condenser fan spins freely, no breakers are tripped. Exterior temps are around high 70s low 80s at night, if it matters. Is there something I can do to fix this?

Thanks - any help is greatly appreciated.
 
  #2  
Old 07-05-12, 07:30 AM
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Set the t-stat to 78 during the day, and hope it stops during the day time so that you can check the unit. Probably one of the pressure/overflow switches caused the problem (just guess now).
 
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Old 07-05-12, 08:06 AM
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I did yesterday - we were home for the 4th and I had it at 78 all day. I was hoping for a failure during the day but it ran and maintained the temperature fine...until nighttime.

Is a technician able to check those switches if the unit is working? Doesn't sound like it?
 
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Old 07-05-12, 08:25 AM
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Not if the unit is working. Don't know why only failed in the evening, You may have to check it at dark by using a flash light. Open the condenser panel, check the contactor button when the unit stops, see if that button is pulled in. if not, push it in with an insulated tool and see if that start the unit. (be careful high voltage in there)
 
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Old 07-05-12, 08:35 AM
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Thanks...I've got no clue what that button would look like pushed in or out, any links or guides out there I can research?
 
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Old 07-05-12, 08:45 AM
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See the thread---- ' How contactor works'..

http://www.doityourself.com/forum/ai...tor-works.html
 

Last edited by Shadeladie; 07-05-12 at 09:37 AM. Reason: Added link to thread
  #7  
Old 07-05-12, 01:02 PM
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Appreciate the help, that was informative. I'll check it out tonight, it doesn't seem to be temperature dependent but can't hurt to look.
 
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Old 07-10-12, 06:29 AM
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Quick update, it's happening during the day now too, condenser unit randomly shuts off at different points throughout the day. Twice in the mornings when coming on, a buzzing noise is heard and the fan doesn't turn - one morning I shut it off manually, and it worked sporadically all day, the other morning I didn't, and it started working again. ?
 
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Old 07-10-12, 07:46 AM
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Now during the day at least you can see better. check contactor button first, buzzing sound usually come from a bad contactor, if it is not pulled in, check to see if the 24V is there, IF it is, replce contactor, if not, trace back to the air handler and try to find out why the 24V power is gone. Also, some unit has pressure switch built in the condenser, that switch can cut the 24V power if line pressure gets too high or too low.
 
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Old 07-10-12, 08:57 AM
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Thanks, will check when I get home. If the issue is not electrical, but a bad contactor or pressure switch, does it eventually fail the unit completely or will it continue operating intermittently?
 
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Old 07-10-12, 12:44 PM
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Hard to say, anything can happen. check the contactor and 24V first, if the contactor is OK, you may need to use multi-meter to find out where the 24V is stopped (before contactor? before or after pressure switch (if you have one)). To catch this type of -on and off- problem, you need to stand right next to the condenser, open the panel, and watch the contactor button, and measure the 24V while it is not working. (High voltage in there, becareful). Tell you what I did once before. I didn't have time to wait and try to catch this type of on/off problem, so I just go ahead replace the contactor, it is cheap, and I was lucky, I was right that time.
 
 

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