Results 1 to 14 of 14
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07-07-2010, 12:01 AM #1
Excessive superheat overheating compressor
Hello
Small bespoke domestic fridge system, approx 15m run to condensing unit along warm external wall. R407C -7 / 3.5 bar LP (Approx) set point 3c
Compressor cycling on thermal protection.
I've opened the expansion valve to 7k superheat measuring the suction pipe temperature AT THE COMPRESSOR, this has kept the compressor cold and all running well.
I am unable to take a pressure at the evaporator and I'm worried by opening the TEV (internally equalised) the compressor will flood in very cold weather.
All thoughts welcome
ThanksLast edited by Contactor; 07-07-2010 at 12:03 AM. Reason: Added 'internally equalised'
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07-07-2010, 12:06 AM #2
Re: Excessive superheat overheating compressor
Prior to opening the valve superheat at the compressor inlet was approx. 23k with pipe temp of about 16c
Last edited by Contactor; 07-07-2010 at 12:09 AM.
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07-07-2010, 12:08 AM #3
Re: Excessive superheat overheating compressor
Hello contactor
You sayopened the expansion valve to 7k superheat
AND what is the superheat when it gets down to setpoint?Quidvis Recte Factum Quamvis Humile Praeclarum.
Latine dictum, sit altum videtur.
Si hoc comprehendere potes, gratias age magistro Latinae.
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07-07-2010, 12:11 AM #4
Re: Excessive superheat overheating compressor
So if for example, the outdoor temperature fell to -10, the compressor could presumably be flooded by a 2 phase mixture reduced to liquid sub cooled by 3k ?
Last edited by Contactor; 07-07-2010 at 12:18 AM.
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07-07-2010, 12:17 AM #5
Re: Excessive superheat overheating compressor
thanks for your reply trash, i think my edits crossed with your post -
fridge was up to 17c temp while cycling on thermal protection
you make a good point about measuring the sh at set point, i'm not sure about that one
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07-07-2010, 12:21 AM #6
Re: Excessive superheat overheating compressor
So if for example, the outdoor temperature fell to -10, the compressor would presumably be flooded by a 2 phase mixture sub cooled by at least 3k 07-07-2010 12:08 AM
So if for example, the outdoor temperature fell to -10, the compressor would presumably be flooded by a 2 phase mixture sub cooled by at least 3kQuidvis Recte Factum Quamvis Humile Praeclarum.
Latine dictum, sit altum videtur.
Si hoc comprehendere potes, gratias age magistro Latinae.
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07-07-2010, 12:22 AM #7
Re: Excessive superheat overheating compressor
wouldnt measuring superheat temp at evap with thermometers be more accurate and is the suction line well insulated?i dont know about using 407c for this application either?
mmm to beer or not to beer...........lets drink breakfast
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07-07-2010, 12:28 AM #8
Re: Excessive superheat overheating compressor
system was commissioned to 7k superheat at evaporator but this wasn't enough to keep the compressor running. The suction line is insulated in 3/8'' black armaflex, but I wondered if this is only making matters worse in the blazing sun as it seems to get very hot.
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07-07-2010, 12:33 AM #9
Re: Excessive superheat overheating compressor
wouldnt measuring superheat temp at evap with thermometers be more accurate and is the suction line well insulated?
dont know about using 407c for this application either?Quidvis Recte Factum Quamvis Humile Praeclarum.
Latine dictum, sit altum videtur.
Si hoc comprehendere potes, gratias age magistro Latinae.
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07-07-2010, 12:38 AM #10
Re: Excessive superheat overheating compressor
system was commissioned to 7k superheat at evaporator but this wasn't enough to keep the compressor running.
16K superheat just from the suction lineLast edited by TRASH101; 07-07-2010 at 12:59 AM. Reason: too mucking fuddled
Quidvis Recte Factum Quamvis Humile Praeclarum.
Latine dictum, sit altum videtur.
Si hoc comprehendere potes, gratias age magistro Latinae.
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07-07-2010, 12:55 AM #11
Re: Excessive superheat overheating compressor
i was of the belief that 407c was high temp refrigerant,dunno havent played with the stuff yet.are the current draws in range if not maybe check for non condesables,condenser air flows,run capacitor etc.
3/8 wall does sound to thin i now use 19mm wall on medium temp stuff and have done so since the tirade of new refrigerants.mmm to beer or not to beer...........lets drink breakfast
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07-07-2010, 01:00 AM #12
Re: Excessive superheat overheating compressor
you say it was commissioned to 7 kelvin was this on 407c or 22 if the later then your condenser size is probably to small,was always under the impression that 407 ran a higher head.
might pay to fit schraeder and reprocess system.mmm to beer or not to beer...........lets drink breakfast
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07-07-2010, 01:11 AM #13
Re: Excessive superheat overheating compressor
You have got to find out what is going on with the suction line. Even uninsulated it shouldn't gain 16k over 14m of pipe.
Quidvis Recte Factum Quamvis Humile Praeclarum.
Latine dictum, sit altum videtur.
Si hoc comprehendere potes, gratias age magistro Latinae.
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07-07-2010, 06:38 PM #14
Re: Excessive superheat overheating compressor
SORRY IT'S 404A !!!!!! my typo, sorry!!
maybe my temps are out slightly, also I only measured them twice and at the same time in the cycle, but generally the SH was high.
This fridge is made of bricks, it's an old archway in a cellar in a big old house with a made to measure steel framed double glazed fridge door on it, it was empty so very low load
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