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BUSHY
26-03-2008, 06:19 AM
can anyone give me an idea of what suction pressure i should have on a frost free fridge running on r134a

dsp
26-03-2008, 07:04 AM
Zero Psi or just above.

dsp

BUSHY
26-03-2008, 09:51 AM
thanks for the heads up dsp

paul_h
26-03-2008, 10:44 AM
About 10-20kpa, depending of course on how cold the fridge is. It won't be 20kpa when it's at ambient and just turned on. It also shouldn't ever be 0kpa either unless the freezer is -30C or iced up.

drew71
27-03-2008, 07:41 AM
I am in no way disputing the information already given, & I am certainly no expert on domestic appliances, I was however involved with some "field to factory feedback reporting" for a white goods manufacturer around the time when R12 was phased out and R134a was introduced.
Recommended service procedures were often ignored in those days (lucky if you could get some guys to replace driers after a compressor change, let alone correctly evacuate or weight charge) vapor charging to 0psi back pressure after service was common practice.
My point is, and this is only from my experience, many domestic R134a units will flood back, sometimes dramatically with even a slightly positive suction pressure, slightly negative pressures at operating temperature seem common.

Cheers

Drew

nike123
27-03-2008, 11:08 AM
I am in no way disputing the information already given, & I am certainly no expert on domestic appliances, I was however involved with some "field to factory feedback reporting" for a white goods manufacturer around the time when R12 was phased out and R134a was introduced.
Recommended service procedures were often ignored in those days (lucky if you could get some guys to replace driers after a compressor change, let alone correctly evacuate or weight charge) vapor charging to 0psi back pressure after service was common practice.
My point is, and this is only from my experience, many domestic R134a units will flood back, sometimes dramatically with even a slightly positive suction pressure, slightly negative pressures at operating temperature seem common.

Cheers

Drew

If you have usual temperature inside refrigerator without freezer box of 3-4C than with TD for that kind of evaporators of 10K you should have evaporation temperature of -7 to -6C.
That converted to evaporation pressure of R134a is 2,25-2,35 Bar absolute.
Converted to Psig that is 18-20 Psig

On the other hand, if that refrigerator have also freezer box, than depending on freezer temperature, pressures are lower.
For example, if freezer reach temperature of -18C with TD of 10K you should have -28C evaporation temperature. If we convert that to Bars that would be
0,93 Bars absolute.
Converted to Psig that is -1 Psig

Hope this clears some things!

nike123
27-03-2008, 11:11 AM
About 10-20kpa, depending of course on how cold the fridge is. It won't be 20kpa when it's at ambient and just turned on. It also shouldn't ever be 0kpa either unless the freezer is -30C or iced up.

Paul, you mean Psig (Pounds per square inch GAUGE) here instead of kpa !:eek:

paul_h
27-03-2008, 11:46 AM
I don't use PSI and I probably never will. Pressures and temperatures are metric in australia.

The note about being in a slight vacuum is wrong too, I repaired thousands of freezers, and recharged by manufacturers stated refrigerant charge in grams. They were never in a vacuum when running, they were a touch over 0 kpa, like 5 or 10 kpa when down to temp.

edit: If that isn't the case then none of the hundreds of compressor changes I did ever had the freezer go below -15C, but they did :cool:

When dealing with larger stuff though, it didn't quite work. I retrofitted r134a to a freezer room in 1996 (not my idea) when r12 was phased out, and the damn thing wouldn't go below -15 without running in a vacuum. But it seems to work on domestics.

nike123
27-03-2008, 12:18 PM
I don't use PSI and I probably never will. Pressures and temperatures are metric in australia.



Sorry, I made mistake here mixing absolute pressures and gauge pressures and that make me think that you mistaking in units.:o

Here, we are working now with Mpa on gauges! Before, there are Bars!

drew71
28-03-2008, 01:35 AM
The note about being in a slight vacuum is wrong

Cheerfully withdrawn, obviously my recollection is incorrect.

Whats really going to bug me now, is that I'm pretty sure the service department I was working for at the time paid insurance claims for water damage to parquetry floors on more than one occasion, caused by dripping/frosted suction lines after service.
Must have been parallax error or gauges not calibrated !

Cheers

Drew

paul_h
28-03-2008, 02:50 AM
That could have been static coils, they'd have a colder suction and lower pressure than fan forced coils. All fridges have a pretty warm suction these days, with the suction lines inside the cabinet (and the condenser too in a lot of cases) for most of the run to and from the compressor.

mwinjuma
11-04-2008, 09:13 PM
Good evening Mr.BUSHY
First I have to ask you that where you live,this is because it depends on ambient temperature and also it depends with sizes of your fridge.But for my little knowledge about this is 10psi or less than 1bar.I told you this because I have already done for alot of fridge and they perform well,but due to my embient temperature in Zanzibar

philfridge
11-04-2008, 09:21 PM
Zero Psi or just above.

dsp
:confused: I have to disagree with this advice this pressure is ok for a freezer but the unit in question is a frost free ffridge . The pressure should be 5 to 8 psi :D keep it between this and you will not go wrong.

paul_h
12-04-2008, 09:01 AM
Fridges shouldn't ice up anyway. When talking about a frost free fridge, people normally are talking about fridge/freezer combinations.
It's the freezer part that is frost free (self defrosting).