House AC Unit troubleshooting


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Old 06-06-16, 08:55 AM
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House AC Unit troubleshooting

Hello,

The issue I am having currently is my house AC unit not spitting out the right temperature differential consistently. For example, I have a programmable stat that is set at 72 when I'm home and 74 when I'm at work. When I come home in the evenings, the house is still at 74 just running along and only spitting out around 71 degrees out of the vents. My solution thus far to fix this is to switch the stat to heat mode, wait the 5 minute delay, let it run in heat for about 60 seconds, switch back to cool mode, wait the 5 minute delay, then read the temp out of the vents again. When I do this, the temp starts spitting out 58 degrees and the house takes about 60-90 minutes to get to 72 degrees and eventually shuts off. When it turns back on, it continues to spit out 58 consistently the rest of the night. Then the next day, the whole process starts over again. I figure it can't be low on refrigerant considering it puts out 58 through the vents when it's working normally. Also, this past weekend was cooler (only 72-75 outside) plus it stays at 72 since I'm home all day and it worked normally and put out 58 degrees. However, as soon as it goes back to weekday mode and sets to 74, something goes wrong and it will only spit out around 71 degrees through the vents. Any ideas what the issue could be? I don't understand why it works normally until it needs to cool from 74 to 72 and that it consistently spits out 58 degrees from the vents when it's working right. And I don't understand that my only solution to fix this is switching the reversing value from heat back to cool to get it to work right. I'm considering just leaving the house at 72 all times to not mess with it.

Thanks for the help!
 
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Old 06-06-16, 09:16 AM
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Pros here will probably want to know the brand and model no's of your equipment.
 
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Old 06-06-16, 10:11 AM
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It would appear that this is a heatpump system ??
It's posted in the A/C forum so based on your reply it may be moved.

When your system should be cooling.... you need to go outside and see what the condensor is doing. If it's not running you wont get any cold. It it is running..... check the larger insulated line at the condensor to see if it's cool or cold.

You may have a reversing valve issue inside the condensor if this is a heat pump. That would require a service tech to diagnose and repair.
 
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Old 06-08-16, 10:23 AM
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Sorry, I'm new and not sure where to post things. I have a Lennox AC Unit and yes it is a heat pump. When the vents are reading 58 degrees, the line is cold and sweating. When it reads 71 degrees, the line is barely cool and not sweating at all. I believe it is the reverse value being stuck but my father-in-law (HVAC Specialist) says it should only get stuck switching from heat to cold/cold to heat, not from staying in cold mode and just turning on and off. He usually is the one who checks and fixes the issue but has not had time to drive to the house as we live far away. With 90 degree temps coming, I was hoping to resolve the issue From what I've told him over the phone, he seems to think it could possibly be the stat (honeywell). Yesterday, I changed it to run 73 during the day and 72 when i get home and the AC was finally not running when i got home for once, the stat read 72, and when it did kick on it read 58 coming out of the vents. I'm going to continue testing this theory for a week but it appears that an issue only arises when the house must cool from 74 to 72. If this is a quick fix then great but what's the point of a programmable stat if I have to leave it set to 72 even when I'm not home...
 
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Old 06-08-16, 01:29 PM
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If the reversing valve was switching to heat the supply temp would be much higher than 71*. Next time it puts out 71* check to see if the fan and compressor are running outside.
 
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Old 06-09-16, 05:19 PM
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It could also be cycling during the day when you're not home & the inside check- valve that is supposed to be fully closed, may be sticking partly open; then the unit will not cool enough to bring the temp down to 72F & will just keep running.

The outdoor check-valve must be fully open in cooling mode.

'Or' the compressor is not running when it's not cooling down to 72F.
 
 

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