AC troubles - several symptoms, need help diagnosing issue


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Old 07-04-10, 09:18 PM
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AC troubles - several symptoms, need help diagnosing issue

Hey, I got several issues with my home AC, any help from someone w/ experience please. It is 2 years old and worked great last year, not good at all this year.

I am having trouble with not enough cooling from my home ac. Here is what I have found so far:

The cooling coil is only cold on the bottom four rows. It also develops light frost on the cap tubes and the 90 degree elbows between the four rows on the bottom are cold and that's it.

The Thermostatic Expansion Valve doesn't really change anything if I put the sensor in hot water for awhile, or very cold water.

I have removed the filters and it makes no difference. I have blocked off the top 2/3 of the cooling coil on each side, the frost dissapeared from the bottom elbows.


I had a friend check and it was only 6 lbs low on coolant, he topped it off but it made no difference. Said it may be a slow leak.

I figured it is a bad thermostatic expansion valve, or air in the refrigerant. What does this sound like to anyone who has experience in this area.

Thanks
Jon Puckett
 
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Old 07-04-10, 10:52 PM
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Sounds like you know A/C system very well. Anyway, is your friend an A/C tech ? How does he know the freon is low ? did he use a guage ?
 
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Old 07-05-10, 08:58 AM
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Originally Posted by clocert
Sounds like you know A/C system very well. Anyway, is your friend an A/C tech ? How does he know the freon is low ? did he use a guage ?
I tend to dive head first into things and research a bunch. My friend works for a Heating and Air company, and moonlights in the evenings under the table. He used gauges to diagnose the system and added some r-22.

I think these symptoms are caused by the high pressure (liquid) side having vapor issues. This system is only two years old, so I think either the leak let in in air over the winter (Not a heat pump so it wasn't used all winter), or the temp sensor for the expansion valve has failed.

I am just hoping someone out there has had the same symptoms as I, and will chime in on what the problem actually was.
 
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Old 07-05-10, 10:30 AM
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Wonder why your AC tech friend does not continue help you after he added the freon to the system? Anyway, air won't get in becuse you have a small leak (unless you opened the system before, like cut the pipe.. etc.). Gauge the low side where the system is not running, you can tell if any air is in the system. While the system is running, what is the temperature(cold/warm/hot) of both pipes near the condenser? If your friend comes again, ask him to get subcool and superheat numbers, that will identify your problems.
 
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Old 07-05-10, 12:35 PM
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Originally Posted by clocert
Wonder why your AC tech friend does not continue help you after he added the freon to the system? Anyway, air won't get in becuse you have a small leak (unless you opened the system before, like cut the pipe.. etc.). Gauge the low side where the system is not running, you can tell if any air is in the system. While the system is running, what is the temperature(cold/warm/hot) of both pipes near the condenser? If your friend comes again, ask him to get subcool and superheat numbers, that will identify your problems.
He lives pretty far away, and has been busy for them with actual paying customers. I don't like taking up his time if it's something I can figure out. I will ask him to check out the subcool and superheat if I can't figure it out on my own.

The small tube is warm coming into the Thermal Valve, and the big tube is cool, but not cold like it was last year. Last year the whole cooling coil and the big tube going back to the compressor was cold enough to condensate. This year only the bottom four rows of the cooling coil on each side condensate.
 
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Old 07-05-10, 02:13 PM
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Most common cause of big pipe not cold is lack of freon. That pipe suppose to be cold and sweaty. not sure if your friend put in enough freon or not, since the system is only 2 years old, I wouldn't worry that much about expension valve now (unless you knew you phycically damaged it.) The problem is you have a leak somewhere. In one year, from cold to cool, you probably lost 1.5-2.0 lb of freon. that leak is not that small, you need to fix that leak first, and then charge it up and see if that fix the problem.
 

Last edited by clocert; 07-05-10 at 02:32 PM.
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Old 07-06-10, 12:06 PM
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you have a blocked coil, a piece of dirt or something got in the line somehow and worked its way into your evaporator coil. that is why it appears to be low, but its not. evidence would be a low suction pressure and high head pressure, and the fact that only part of ur coil gets cold.. you also dont have any leaks, i promise. you need to evacuate the system and blow out the lines if possible, or replace the coil and make sure if u do, install a filter line drier to prevent this from happening again. message me if you have any questions
 
 

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