Conversion (retrofit) old R12 FREEZER to R600a with new R600a compressor

[brik32544]

I would like to make an old freezer which works extremely well (but uses too much power) to a more power efficient freezer.

I intend to use R600a and not R134a because:
a) the R600a compressors are more efficient and
b) R600a is readily available and cheaper than R134a (and does not unduly enrichen Dupont and Honeywell ;) )
c) it does not require a change of oil like a R134a retrofit

I know that R600a is flammable and that the electrics must be R600a compatible (the compressor is obviously a big part of this.
The old freezer has been working for more than 30 years so leaks have not been an issue...but I will thoroughly check for leaks when I make the changes
Obviously I would change the filter/dryer.
There are many R600a compressors available and I need some help on
1) the sizing of the compressor
2) quantity of R600a to be used.

Have any of you experts or "experimentators" got any advice?

[seadanzig]

hi
the amount of money it will cost to replace the compressor to retrofit a 30 year old freezer isnt viable. the money you will save will take a long time to recoup back

[tonto33]

you will need a 1/6th compressor on r600a and start with 23grams of gas

[1mikeefc1]

The main component of the freezer is the compressor so as good as your old freezer is it will still have a new compressor, I would agree with the previous comment that cost and time wise would be better to just replace the freezer personally.

[brik32544]

hi
the amount of money it will cost to replace the compressor to retrofit a 30 year old freezer isnt viable. the money you will save will take a long time to recoup back

I am using this project as a learning experience.
The cost of a 350-400l liter chest freezer is around 4-500 euros
Admittedly the insulation in the body of the freezer could have seen better days and so it may well be that the compressor would use up more power than a new one.

A new compressor (with specs mentioned in the next reply), costs about 100 euros

Hopefully the repair should cost no more than 130 euros for compressor, gas and the capacitor, PTC plus my labour ( I am debiting this to my continuing education :))
Usually there are many fridges being thrown out, I wish i could find one now..... It would have all the electrics already there...

[brik32544]

you will need a 1/6th compressor on r600a and start with 23grams of gas

Thanks tonto33, I found a shop that sells a ZEM HQY 75 AA for around 100 euros. The specs are

Displacement (cc) 6.64
Power (HP) --
Power Absorption (Watts) 74
Run/Start Current (Amps) 0.53/81
Run/Start Winding (Ohm) 25.2/22
Rated Power (kcal/h) 92

How can one estimate if it is a good compressor for the job? Maybe there is a formula which can be applied to see if we are in the ballpark? Or is this better done as a trial and error?
I guess I should get the old compressor specs and the qty of gas inside it

[brik32544]

The main component of the freezer is the compressor so as good as your old freezer is it will still have a new compressor, I would agree with the previous comment that cost and time wise would be better to just replace the freezer personally.

Yes, this is not a money making venture but just to see if I can pull through this little exercise. Something tells me I should look up some fridge design handbooks... but I am not finding it difficult to postpone this as much as possible....:)