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Old 05-02-2013, 07:16 PM   #1
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Cold cutoff temp to run a A/C piston compressor


Don't know if humidity is a factor, but could someone speak to what is too cold to run central air in Cincinnati, Ohio (on the Ohio river). Different opinions online, and most of the systems in this mobile home park are older, with piston compressors and no low ambient temp switches, nor any owner manuals to check.

There is one COPD patient who wants to run his old Miller packaged unit too early in the season to dehumidify the air. He's been ignoring my suggestion to run the fan only or get a dehumidifier.
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Old 05-02-2013, 07:57 PM   #2
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Cold cutoff temp to run a A/C piston compressor


That answer varies somewhat with the system. A low air flow system might begin to freeze the coil when its 70 outside. While a system with good duct work so it has lots of air flow may work fine when its 60 outside.
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Old 05-02-2013, 10:11 PM   #3
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Cold cutoff temp to run a A/C piston compressor


install a head pressure control to turn the condenser fan on and off
to keep head pressure up. I had a nursing home that was going through
compressors in the winter by all the nursing stations. The nurses were turning on the ac in the winter because the patients keep their room at 85 degrees and the heat went into the hallway by the nurses station. I installed head pressure contols so they can run the units in low ambient temps.
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Old 05-03-2013, 09:22 AM   #4
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Cold cutoff temp to run a A/C piston compressor


You can technically run it down to 50F which is the setting for a low ambient control if it had one. It will have a low load and may freezeup at 60F. I would tell him it is cheaper to run a dehumidifier and more comfy as he must be getting extra cold with the AC on. If he is renting the trailer then he does not care if it breaks down as the landlord will replace it BUT you can tell him he may be greatly uncomfortable and sweating while waiting for a new one too arrive. Got to appeal to their self interests and if he does not want to do without one maybe he will listen.
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Old 05-03-2013, 02:53 PM   #5
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Cold cutoff temp to run a A/C piston compressor


Thx Yuri, been~ and hvac~,

He's the owner of trailer, but hasn't listened to me yet, regarding repeated episodes (over the last two or three years) of icing up the evap. and compressor. Nor will he keep a filter in the return air slot of his floor.

It's icing up again now - evaporator is dirty, but not sure if it's enough to cause the icing. Maybe 50 percent, and I know that's not the only thing that can cause icing. Gonna go clean it first, tomorrow, and do the stuff I know how to do anyway (ohms check the compressor, comp. amp draw, check blower amp draw, blower wheel for dirt, check capacitor specs, contactor and its points) - then see what happens.

Anyone care to take a shot at a percent of blockage (dirt) it might take to ice up the evap in one of these Miller package units for a typical 14' x 70' mobile home (sorry - don't know the tonnage of the unit)...under all other favorable conditions, that is... High humidity climate, on the Ohio River in Cincinnati.
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Old 05-03-2013, 04:51 PM   #6
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Cold cutoff temp to run a A/C piston compressor


if the evap is very dirty and been seriously neglected then the dirt is inside the rows of coils and it needs to be sprayed with coil cleaner and thoroughly cleaned. face dirt is obvious but the internal stuff you cannot see and needs to be washed out. there is no percentage. tell him he is destroying his compressor when it ices up as liquid refrig is slamming into his valves. should only have vapor down the suction line but when iced up then liquid slugs back to the compressor.
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Old 05-03-2013, 05:03 PM   #7
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Cold cutoff temp to run a A/C piston compressor


The cooler it is outside, the less dirt it takes to freeze up the coil.
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Old 05-03-2013, 06:29 PM   #8
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Cold cutoff temp to run a A/C piston compressor


Thank you Yuri & been~

I know I don't have to tell you how much that helps! (but I will anyway)....

Thx so much, that really helps!
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Old 05-03-2013, 07:15 PM   #9
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Cold cutoff temp to run a A/C piston compressor


http://www.icmcontrols.com/HEAD-PRES...-Prodlist.html
Throw a freeze stat on the coil too. I'd want a txv on there to avoid the liquid flood back that's going to happen.
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Old 05-03-2013, 08:03 PM   #10
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Cold cutoff temp to run a A/C piston compressor


I think that old Miller unit is going to bite the dust soon if it has been frozen up that many times. That washes oil out of compressors and destroys them.

Yur Welcome too.
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Old 05-04-2013, 06:42 AM   #11
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Cold cutoff temp to run a A/C piston compressor


Thx Marty~ - The head pressure is strictly an electrical add-on? I need to go back to that link you gave me and read some more. When I first read your suggestion, I thought it would require brazing something into the lines (maybe it still does?).

Was just reading about that Yuri - I reckon he'll sit up and take notice then (when it bites the dust)

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Old 05-04-2013, 08:35 AM   #12
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Cold cutoff temp to run a A/C piston compressor


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Last edited by yuri; 05-04-2013 at 10:28 AM. Reason: viewed Martys link
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Old 05-04-2013, 08:57 AM   #13
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Cold cutoff temp to run a A/C piston compressor


Quote:
Originally Posted by justplumducky View Post
Thx Marty~ - The head pressure is strictly an electrical add-on? I need to go back to that link you gave me and read some more. When I first read your suggestion, I thought it would require brazing something into the lines (maybe it still does?).

Was just reading about that Yuri - I reckon he'll sit up and take notice then (when it bites the dust)
Yes those are strictly electrical. They adjust the condensor fan speed based on the temp of the condensing coil,temp sensor included. When it's around freezing outside it will cycle the fan on and off. Above that it it acts like a freq. drive. and runs the fan at whatever speed needed to keep the coil around 100 degrees. You get a much better fan motor life than using the on/off pressure switch activated low ambient controls.
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Old 05-06-2013, 04:13 PM   #14
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Cold cutoff temp to run a A/C piston compressor


Thank you Marty~
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