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Modding chest freezer to run 404A to achieve -30F box temp

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ICanHas

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Discussion starter · #1 ·
To keep the box temperatures between -25F to -30F which you can't get with R134a without running at 18" Hg of vacuum or so while 404A would give about 5psig

This product I came across online looks exactly like a household chest freezer. The cabinet design, the coated aluminum interior and the location of drain and control.

It looks like they buy household freezers and mod them with off the shelf temperature controller and run it on 404A to get the temperature range they get.

http://www.scientemp.com/pdf/34-07 Spec Sheet.pdf

Can you mod an HFC-134a to run cooler on HFC-404A with just a change to capillary tube or do you need? What exactly needs to be modded to make this work right?
 
#2 ·
i would think it would have to have thicker insulation and/or a larger compressor than its conventional deep freeze counterpart, but that sure as heck looks like a standard freezer with a digital control screwed to it.
 
#3 ·
Compression ratio is diff on 404 vs 134, so doubt 134 compr. would work the way U want, and would prolly need diff cap tube, or just use 404 TXV. Not sure about evap tubing and cond. coil, tho. Need a full time refer guy to chime in
 
Discussion starter · #4 ·
When I look at compressor catalogs, I see ones that lists 404A/22 for LT & MT as well as 134a though.
Danfoss 120U8057 lists 404A, 507, 22 and 134a as compatible.

As for that freezer I found online, it says the compressor is 1/8hp, which is a household freezer size compressor.
I know True brand freezers for food service use in 5-7 cu ft range uses 1/3 hp.

Even with 1/8 hp, chest style with infrequent opening in 70-80F air conditioned space should be able to maintain -20-30F considering standard freezer is designed to hold 0F at 105F or so (what I read in manual)
 
#6 ·
One approach to this might be to do a bit of reverse engineering.

If you have an R134A chest freezer, which would have a design temperature of about -10ºF, and you want it to run at -30ºF, first determine what its R134A compressor capacity is at say, -20ºF SST. Then select a R404A compressor with a similar or slight greater capacity at at -40ºF SST.

Then you need to select a capillary tube suitable for that capacity with R404A at the new conditions.
 
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Discussion starter · #7 ·
Ihaven't seen a 1/8hp rated for 404A. I really think that thing is just household fridge modded to run 404. but its too costly to just get one to reverse engineer.
 
#8 ·
ICanHas said:
Ihaven't seen a 1/8hp rated for 404A. I really think that thing is just household fridge modded to run 404. but its too costly to just get one to reverse engineer.
Click to expand...
If you want to play, you gotta pay. ;)

If you had two compressors, each rated at the same capacity for the same conditions, one designed for R134A and the other for R404A, the R134A compressor would typically have about 60% greater displacement that the R404A compressor. To be able to "mod" an existing system with an R134A compressor by changing refrigerants and a cap tube is highly unlikely to work because the R134A compressor would demand about 60% more power from its motor...which it hasn't got...and so it'll overload and shut down.
 
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Discussion starter · #9 ·
Hmmm so how does Danfoss 120U8057 have rating for both 134a and 404A?
Small drives are affordable these days, so maybe i'll slow the motor down with a VFD.
 
#10 ·
i used work for a manufactuer and we used to do this all the time , standard chest freezers , we would remove compressor, stat etc , replace compressor [ 502 then] new temperature control add an extra condenser we used an in house made back plate one, and we sold them as - 40 , they where a very poular line ,
 
#11 ·
If you were to find the performance data sheets for this compressor with R134A and R404A, I believe you would discover that on R134A it's running at a medium/high temperature and with R404A at low temperature.
 
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#12 ·
ICanHas said:
Ihaven't seen a 1/8hp rated for 404A. I really think that thing is just household fridge modded to run 404. but its too costly to just get one to reverse engineer.
Click to expand...
Haven't seen a 1/8 hp freezer with the listed amp draw in that spec either :)
You might look for a used Dipin Dot freezer if you got a little project. Bet it would be cheaper than something with a scientific tag :.02:
 
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#13 ·
That 1/8 HP stated in the linked freezer specs is probably a misprint. It's more likely a 1/3 HP compressor.

I checked Embraco's site for R404A LT compressors and they list a 1/5 HP which has a FLA rating of about 3 amps and the 1/3 HP at about 6 amps. That would make sense.

http://www.embraco.com.br/catalog/busca_avancada.aspx?produto=1
 
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#14 ·
Wouldn't running a normal "cold-wall" type chest freezer at -30 degrees just cause the inside of it to get smaller and smaller due to massive ice buildup on the walls, or would it be about the same as a 0 degree freezer? Or were these the kind with a fan inside and auto-defrost?
 
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Discussion starter · #15 ·
What's the relationship between wall temperature and frost build up? I don't think its too bad with chest type as the outside air infiltration is minimal compared to front load type.

The water removal from contents would be reduced, no? The lower temperature reduces vapor pressure/sublimation rate. This is why its said that ultra cold freezing reduces freezer-burn. Granted, not sure how effective this is at -30F
 
#17 ·
R134A chest freezers at -40

Yes, I've designed hospital plasma freezers (-35 holding, I believe) out of household chest freezers.
But my refrigerant of choice was R411B. They would peg the -40 test thermometers.
We had the advantage of "no-break" hospital AC and controlled 72f ambient.
I did these in 1998 and one is still operating in our nearest city hospital, only repair being the aux fan.

I'm north on the trapline now, so my other mods are not at hand.
 
#19 ·
used to do this all the time , standard chest freezer , remove compressor and thermostat . fit r404a low back pressure compressor , danfoss oil seperator , add an extra condenser to the rear of the cabinet , thermostat and thermometor , the original air cooled condenser and condenser fan motor were retained , no cap tube alteration , they where sold as -40 c/f. , esta or elcold where the brands at thetime .
they were a very big seller .
 
#20 ·
COOLJIM said:
used to do this all the time , standard chest freezer , remove compressor and thermostat . fit r404a low back pressure compressor , danfoss oil seperator , add an extra condenser to the rear of the cabinet , thermostat and thermometor , the original air cooled condenser and condenser fan motor were retained , no cap tube alteration , they where sold as -40 c/f. , esta or elcold where the brands at thetime .
they were a very big seller .
Click to expand...
mmkkkk
 
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