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Old 03-19-2009, 09:28 PM   #1
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compressor replacement blues


I recently replaced the Copeland Scroll compressor on my 12 year old 12 seer 5 ton Rheem condensing unit. I purged the lines and coils with nitrogen, flushed with Quik-SF, evacuated, broke the vacuum with nitrogen, pressure tested with nitrogen, evacuated and charged. The liquid line drier was replaced and a suction line filter placed. The capacitor and contactor were replaced. On initial start-up the charge was too low and the compressor shuttered and stopped when the suction pressure dropped too low. I added R22, and the system operated appropriately, and cooled well. I planned on checking the system for acid and removing the suction line filter after a week, but after running well for 6 days, the a/c stopped cooling. The breaker (40 amp) had tripped. After resetting the breaker, the compressor will not start, although the fan runs. The breaker did not trip, but it did hum, suggesting high current draw, but I have not put a meter on it yet. Of note, I did not remove any oil from the new compressor, as I felt as though I removed most of the old oil with the flush. Could the compressor be locked from excess oil? Any ideas?
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Old 03-19-2009, 09:39 PM   #2
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"compressor shuttered and stopped when the suction pressure dropped too low"? How low was it? If it slugged liquid it may have bent the scrolls and you now have a "locked rotor". They damage easily.

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Old 03-19-2009, 09:44 PM   #3
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It dropped to about 25 psi on the guage. The compressor ran fine for 6 days after the charge was corrected.
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Old 03-19-2009, 09:55 PM   #4
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Is it possible the suction line filter stopped up & starved the compressor . May have just been a bad compressor. Mechanical things just fail sometime
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Old 03-19-2009, 09:56 PM   #5
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Probably still part of the problem that killed the first compressor.

Suction filter should have been changed within 3 days.

And that is when the system should have been rechecked for acid.

Try putting a hard start on it, to see if it will start again.
If not, consider a new system
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Old 03-19-2009, 10:02 PM   #6
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The first compressor was wired with 10 guage and a 30 amp breaker, which would trip every month or so. I changed it out to 8 guage and a 40 amp breaker, and found an area in the old wire where a short had developed. I figured that the voltage drop with the old, inadequate wiring, the short, and a 12 year old capacitor contributed to the first compressors demise.
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Old 03-19-2009, 10:07 PM   #7
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25 psig for r22 is quite low. below 30 and I would get worried. May have had oil return or circ problem at that low pressure. How long did it run before it did the shutter/stop biz. The old recip compressors could handle a LOT of abuse which the scrolls cannot.
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Old 03-19-2009, 10:12 PM   #8
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about 10 seconds, off for about 10 seconds,started up again, and stopped after about another 10 seconds, at which time I pulled the disconnect. I added another 2 lbs of R22, and it ran fine with suction 45 psi and high side adjusted to 145 psi at condensor air temp of 65 degrees.
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Old 03-19-2009, 10:15 PM   #9
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Is this a heat pump, or straight A/C?
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Old 03-19-2009, 10:16 PM   #10
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I'm assuming that the compressor shutter stuff was caused by the low pressure switch opening the contactor, and then closing almost immediately when the pressure rose. I'm assuming that the compressor could not start at that point because of the head pressure.
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Old 03-19-2009, 10:17 PM   #11
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Straight a/c with gas furnace
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Old 03-19-2009, 10:19 PM   #12
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Is this unit commonly used for cooling during low ambient conditions?

Because letting it run with a low vapor pressure like that, is going to harm the compressor.

plus, if it doesn't have a CCH its going to wash out the compressors oil.
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Old 03-19-2009, 11:04 PM   #13
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No, its is not normally run at low ambien temperatures. We haven't had much warm weather, and I had the time to replace the compressor on the 65 degree day, so I replaced it then. Didn't want to face the wife's wrath if the A/c wasn't running on the first 80 degree day!
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Old 03-20-2009, 02:58 AM   #14
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you need to put an amprobe on it and see if its even attempting to start if so try the hardstart is this an expansion valve system? if so it should have the hardstart anyway
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Old 03-20-2009, 07:02 AM   #15
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Yes, it is a TXV system.

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