Central A/C repair vs. replace

Just wondering if there's a rule-of-thumb on replacing vs. repairing central A/C units?
My home in MA is 8 years old, and has a (rather cheesy looking) "Concord" system installed when it was built. Last night it stopped cooling - the inside & outside fans run, but no compressor sound, warm air, and the lights dim every 30 seconds or so like the thermal overload is cycling. I shut it down last night and tried again in the AM with same symptoms.
So I guess the real question is, if it comes down to replacing outside unit + inside coil vs. just replacing the compressor (do people even do this any more?), what's the best choice? I assume the newer units are more efficient, but how long would it take to recoup an additional $1000 or $1500 cost?
Eric
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On Tue, 17 Jul 2007 12:55:50 -0400, Eric wrote:

Could be something simple like a start capacitor which would be under $200 to replace. If that's the case and the unit cooled your home well, fix it.
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Wouldja beleive it doesn't even have a start cap?
I opened it up for a few quick checks this morning. Motor has 3 leads, one goes to L1, one goes to L2, 3rd goes to L2 via a 40uF cap (which measured 39uF on my multimeter). By L1 and L2 I mean after the contactor, it's a 2-pole so both sides of the line are switched. The fan of course is after the contactor too and it runs fine, so to me that rules out the contactor.
Wiring diagram shows a start relay and cap with dotted lines and a notation "if equipped", doesn't look like mine is!
Eric

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Do you know how completely rediculous that sounds?
"doesn't have a start cap"
"3rd goes to L2 via a 40uF cap (which measured 39uF on my multimeter)"
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Do you know how completely ridiculous *that* sounds?
A "start" cap is paired with a relay, is in the circuit when starting, then when the motor's up to speed the relay opens and current no longer flows through the cap.
A "run" cap is in the circuit all the time, which is the case with my unit.
Eric

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Well, you knew the difference. :-)
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Yeah and since the tech came yesterday, now I know it ain't gonna run no matter how many caps you connect to it! :^(
Time for a new system... ugh.
Eric

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Doesn't much sound like a compressor. Likely an electrical problem or you've sprung a refrigerant leak.
If it worked OK before, you wanna identify the problem. Call a HVAC technician unless you've got a friend that can troubleshoot AC properly.
P
"Mit der Dummheit kaempfen Goetter selbst vergebens!" -Friedrich Schiller
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At 8 years, it is well worth repairing. Could be a simple fix for a couple of hundred as opposed to a few thousand for a new system. As for the additional cost of energy efficiency, just run the numbers. $1500 may not take all that long over the 15 year life of the system., especially at MA electric rates.
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No doubt you have checked for a reset button on the unit. If not, do so. It appears you are jumping to conclusions without sufficient information to make a decision. I'd suggest you get some professional advice and then make a decision. Bob-tx
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Bob wrote:

they condemn the compressor get several Tech's troubleshooting opinions. The actual operating efficiency of the new higher SEER units depend on a lot of factors. All the factors affecting efficiency have to be right to ever get the rated SEER efficiencies! http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
- udarrell
--
WISDOM PRINCIPLE DIRECTED EMPOWERMENT COMMUNICATIONS -
THE REAL POLITICAL ISSUES and WISDOM BASED PEOPLE EMPOWERMENT
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Reset button is going to make his lights dim every 30 secs???? Oooook!
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If it actually turns out to be the compressor, replace the complete system.
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