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John, Home Appliance Technician
Category: Appliance
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Experience:  Appliance repair business owner for over 43 years.
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After having an HVAC technician recover the R12 from my Sub

Customer Question

After having an HVAC technician recover the R12 from my Sub Zero 532, I installed new compressors (both refrigerator and freezer) along with new filter driers. I then pressure tested the system at 250 psi and fixed a couple tiny leaks at the new braze joints. Next, I vacuumed the system for several hours and then released the vacuum slowly through the filter driers (see next paragraph).
I'm trying to charge the systems with Maxi-Frig MX12a (environmentally friendly blend of propane and isobutane). According to their technical data, I'm supposed to only use 35% of the weight specified for R12 and this refrigerant is supposed to be charged into a system without a vacuum (0 psi system pressure). I did that and neither the freezer or fridge got very cold (around 35F to 40F). I added more refrigerant until the frost line moved up the suction line just past the evaporator, but, the evaporators never fully frosted (about 60% of evaporator was frosted on both evaporators). Neither the freezer nor refrigerator got as cold as they should be .
My freezer superheat is about 30C and the subcooling is about 21C. It seems that both these numbers are too high indicating restriction in either the filter drier or capillary tube (maybe I flowed too much braze material into the cap tube to drier joints and partially plugged them).
My question is this: what target values should I use for subcooling and superheat on both the freezer and refrigerator sides (after I fix the restrictions in the cap tubes)?
Submitted: 6 months ago.
Category: Appliance
Expert:  Appliance Guru replied 6 months ago.

One moment while I get some information for you!

Expert:  Appliance Guru replied 6 months ago.

Hello and thanks for using this service! If you are a JA Member I would like to personally thank you and welcome you back! I am Appliance Guru an extremely experienced tech on the site and I try to get to as many customers as I can. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly, I do not know your skill level so please try and let me know if I am going beyond your knowledge or comfort zone thanks! I strive for a 5 star rating from everyone especially our JA members.


Yes you may have got some brazing material in the cap tube or the drier could be plugged up. What are the pressures?