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Old 08-30-2011, 10:26 PM   #1
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can a single phase scroll reverse?


Just like the title asks, some friends of mine called me yesterday because their Goodman rtu was making a strange noise and had seemed to stop cooling.
Apparently about the time the unit started acting up, the t.v. quit and so did the computer but they never mentioned if the power went out, or if they had a quick brownout. Whatever it was, it happened fast enough that they really didnt notice it happen.
They called me about 15 minutes after it happened, to tell me what was going on with the unit. She said she could hear a strange noise resonating down through the living room ceiling, kinda like the unit was loping. I told them to shut it down and wait a few minutes and then restart it, when they did, all was well.
We were running about 110 degrees yesterday, is it possible that with the quick loss of electric, that their compressor could reverse? What else would cause something like that to happen? I've never seen one like this before. I stopped by there today and the house was a comfortable 72 degrees.

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Old 08-30-2011, 10:40 PM   #2
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can a single phase scroll reverse?


If it was 100 out and the house was 72,there seems to be no problem.
I think if I had made a trip to the house,I would have at least checked the capacitor.
If a condenser loses power and then trys to restart right away then it was probably trying to start under a refrigerant load.That is why most thermostats have a built in 5 minute delay built in to them to give the freon system time to balance out.

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Old 08-30-2011, 11:02 PM   #3
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can a single phase scroll reverse?


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If it was 100 out and the house was 72,there seems to be no problem.
I think if I had made a trip to the house,I would have at least checked the capacitor.
If a condenser loses power and then trys to restart right away then it was probably trying to start under a refrigerant load.That is why most thermostats have a built in 5 minute delay built in to them to give the freon system time to balance out.
A battery powered thermostat doesnt know when you have a quick cut in power or a brownout, so the 5 minute delay in their case would have been useless.

The unit was working fine after i told them to shut it down yesterday and it is working fine today, thats why I'm curious about the strange noise it was making and the loss of cooling after the quick power cut, until they shut it down and restarted it.
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Old 08-30-2011, 11:10 PM   #4
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can a single phase scroll reverse?


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A battery powered thermostat doesnt know when you have a quick cut in power or a brownout, so the 5 minute delay in their case would have been useless.

The unit was working fine after i told them to shut it down yesterday and it is working fine today, thats why I'm curious about the strange noise it was making and the loss of cooling after the quick power cut, until they shut it down and restarted it.
Have you ever listened to a compressor trying to start with a liquid slug.It not only makes strange noises it wiggles and shakes.
I was only using the thermostat as a way to explain why there should be a 5 minutes pause before trying to restart a compressor that has lost power and wants to start before the system was balanced,I.E. no liquid slug.
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Old 08-31-2011, 07:34 AM   #5
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can a single phase scroll reverse?


I think your first assumption was correct. I have had scrolls start up backwards and they do make a strange noise doing it. I also have just turned off the power and restarted and all is well. Doesn't happen often, but I have heard of it enough times to know it is an occassional occurance.
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Old 08-31-2011, 07:40 AM   #6
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can a single phase scroll reverse?


Yes, brief power interruptions (less than 1/2 second) can result in a powered reverse of a single phase scroll according to Copeland....google Application Engineering bulletin AE 4-1312.

Discharge gas expands backwards thru the scrolls and if power is re-applied they continue to orbit in reverse. Eventually this will self correct as the compressor will trip on the motor protector due to high temps, and then restart and run normally when the protector resets.
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Old 08-31-2011, 02:14 PM   #7
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How about a time delay relay? If I add one to the unit, would it be able to catch a quick cut like that?
The neighborhood this unit is in is old and has had some bad power issues in the past but according to the home owner, the power company has been trying to upgrade the area.
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Old 08-31-2011, 02:20 PM   #8
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can a single phase scroll reverse?


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Have you ever listened to a compressor trying to start with a liquid slug.It not only makes strange noises it wiggles and shakes.
I was only using the thermostat as a way to explain why there should be a 5 minutes pause before trying to restart a compressor that has lost power and wants to start before the system was balanced,I.E. no liquid slug.
The compressor definately was running. I'll see about adding a time delay relay to the unit. I installed this unit about 4 years ago and its had zero issues until this happened but I'm glad to see it didnt warrant a major repair.
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Old 08-31-2011, 03:18 PM   #9
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can a single phase scroll reverse?


Sammy,

Copeland says the delay on break time would need to sense 1 line cycle or .016 seconds @ 60hz. I don't see much detail on the ICM timers like model 200 or 201 on their website....but you can call ICM @ 800-365-5525 and ask them directly how brief of an interuption their devices respond to. I think the answer is yes then can do it but they might advise a specific model. Good luck.
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Old 08-31-2011, 05:13 PM   #10
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Sammy,

Copeland says the delay on break time would need to sense 1 line cycle or .016 seconds @ 60hz. I don't see much detail on the ICM timers like model 200 or 201 on their website....but you can call ICM @ 800-365-5525 and ask them directly how brief of an interuption their devices respond to. I think the answer is yes then can do it but they might advise a specific model. Good luck.
Thanks for the info. I'm using a couple of those ICM delays in my swamp coolers at home, they seems to do their job. I'll give them a call and see what they have to say about it, either way it's cheap insurance for future issues.
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Old 08-31-2011, 05:57 PM   #11
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can a single phase scroll reverse?


The check valve in the top of the compressor has come out of place. If this is a straight cool then you need a time delay. If its a heat pump you can relay the rv and equalize the system after shutdown.
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Old 08-31-2011, 06:14 PM   #12
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can a single phase scroll reverse?


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The check valve in the top of the compressor has come out of place. If this is a straight cool then you need a time delay. If its a heat pump you can relay the rv and equalize the system after shutdown.
So you are saying to de energize the RV after shutdown? Wouldnt we still want a time delay on the compressor also to keep form restarting on a quick power cut?
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Old 08-31-2011, 06:31 PM   #13
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can a single phase scroll reverse?


Is the thermostat running off of batteries?
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Old 08-31-2011, 06:45 PM   #14
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can a single phase scroll reverse?


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Is the thermostat running off of batteries?
Yes, batteries in the stat and they dont have an extra wire for C, so I'll have to add a time delay.

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