AC compressor shuts off after 20 min

Hi -
I've been having AC/heat issues since January. Basically - after running for a period of time anywhere from 20 min to 1 1/2 hours, the compressor will shut off. The fan remains on, air is still coming through the vents but is neither heated nor cooled. This is a 12 year old Trane heatpump.
i've now had 3 people look at this:
tech 1 said that the compressor was bad, and at minimum i needed a new one, but that that may not fix the problem. he also directed me at new units. (this was in february)
tech 2 a friend of a friend with his own ac business said that there was a small leak, but that the unit was overcharged anyway and this was not causing the issue(yet). (this was also in february) he cleaned out the outdoor unit, and said to see if that helps. he said it was not the compressor. this didn't help though and i tried calling him back but he seems to have disapeared.
tech 3 said that there was indeed a leak and that it was only 1/2 full of freon.(this was last thursday - April) he fixed the leak and ended up flushing the unit of freon(not intentionally i guess) and then refilling it(but he only charged me for 1/2 the freon, nice). that day i had the unit running for about 2 hours - with no issues. i then turned it off because i'm in AZ and the weather was too nice. i thought it was fixed.
i turned it on again this weekend and started experiencing the same issue - the first time i turned it on the compressor stayed on 40 min, so i turned the thing off and turned it back on again later - with the compressor only staying on 15 min. the company whom tech 3 works for is sending someone out again tomorrow to look at it.
any advice? any experience with this sort of issue? it sounds like there is a pressure issue in the system somewhere - but where could it be? i'd rather not have to have a 3rd appt this week to look at it... i just want it fixed.
Thanks, Jenni
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QueenTiye wrote:

instrument, etc. Do some heavy reading so you can ask questions. Check the temperature split on the condenser outside & the temp split inside. http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
Follow the links. - udarrell
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WISDOM PRINCIPLE DIRECTED EMPOWERMENT COMMUNICATIONS -
THE REAL POLITICAL ISSUES and WISDOM BASED PEOPLE EMPOWERMENT
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wrote:

Reading wont help. Find a competent tech. Tech 1 was your first mistake. Dont find one like him. Tech 2 was your fault. A friend of a friend shit never works. Your 3rd shot was better but unfortunately it seems that tech didnt figure it out either. At least they are going to send someone else out. It could be lots of things. Hopefully they will get it right this time. Good Luck. Bubba
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When the compressor shuts off, does the OUTDOOR fan continue to run?
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I see you are in Arizona.
Do you have a LOAD SHEDDER installed in your home to limit the peak demand of electricity? A load shedder will turn off the compressor just as you describe.
Mark
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You live in Arizona...Do you have a LOAD SHEDDER installed in your home to reduce your PEAK electricity consumption. A load shedder will turn off the compressor from time to time.
Mark
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Thanks for the replies... it seems that it was a simple freon leak -
now why didn't the first guy see that? grrr... trying to sell me a $2000 compressor i suppose!
anyway - guy #3 did a poor job welding, and guy #4 redid it and it appears to work.
thanks again.
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