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09-18-2012, 06:05 PM #1
Modding chest freezer to run 404A to achieve -30F box temp
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.
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?
09-18-2012, 11:24 PM #2Professional Member
- Join Date
- Jun 2003
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.
09-19-2012, 11:24 AM #3Professional Member
- Join Date
- Sep 2007
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
09-19-2012, 04:39 PM #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)
09-25-2012, 07:41 AM #5
09-25-2012, 09:19 AM #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.
09-25-2012, 04:34 PM #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.
09-25-2012, 06:22 PM #8
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.
09-25-2012, 10:53 PM #9
09-26-2012, 12:07 PM #10
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.
09-25-2012, 09:44 PM #11
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.
09-25-2012, 09:52 PM #12Professional Member
- Join Date
- Jan 2008
- LEHIGH VALLEY, PA
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 ,
09-25-2012, 10:05 PM #13
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.