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View Full Version : R12 12 volt Danfoss Compressor to R134a







teemyob
09-10-2014, 12:22 PM
Hello,

I hope you clever folks could help me out.

I have changed a very old R12, 12 Volt compressor on a very small narrow boat fridge for an R134a 12 volt.

The Small Ice Box Refrigerator is hand made, was originally built using a 20 odd year old LEC ice box evaporator. There was no refrigerant charge on the hand stamped plate.

So, I replaced the compressor and have charged it with R134a to around 0 (Zero) Psi. Ran for 2 hours with no ice on the suction, just slight sweat.

The client has been back on to say the appliance cools but runs 100% of the time, draining his limited battery bank (Ah's unknown to me at the moment).

A mate of mine has suggested that I change the refrigerant to R49 !? With a charge of 10% less than that of the original (unknown of course).

I was thinking maybe R600a instead?

I have used R600a in an R134a job before. But not sure about the compatibility of R49 in R134a compressors.

Any help, suggestions or advice would be greatly appreciated please?.

TM

Rob White
09-10-2014, 12:36 PM
.

Keep with the R134a for now, it is just a little bit under charged.

A fridge in case temp of about +5 will have an evap temp of about -5,
the pressure of 134a at -5 is about 1.4 bar ( 20psi).

You need to have a back pressure of about 1 and a bit bar for it to
have enough refrigerant. If it freezes back down the suction you have
put a bit too much in.

Rob

.

teemyob
09-10-2014, 02:07 PM
Thank you Rob.

I was taught an Evap Temperature difference should be around 10 to15c?

TM

Rob White
09-10-2014, 03:01 PM
Thank you Rob.

I was taught an Evap Temperature difference should be around 10 to15c?

TM

Evap temps are very general and can vary.

Most often, most engineers work to approx 10 degs diff.

Some sytems can be as low as 3 and some as high as 15 degs
but for most evaps it's about 10 (ish)

regards

Rob

.

Rob White
09-10-2014, 03:06 PM
.

I did a job on a 12 volt fridge in a canal boat once,
lovely little thing and in a very picturesque setting.

It's a shame the owner tried to defrost the thing with a knife :D
The evap had more holes in it than a Swiss cheese.

Rob

.

teemyob
09-10-2014, 06:55 PM
Thanks again, I will go back and charge again to around 10 psi(g)?

mikeref
10-10-2014, 08:19 AM
Don't forget: The Danfoss BD 2.5 used mineral oil with R12. With R134a, you should be using synthetic oil.