Hi again,

I have the possibility to obtain some R507, and a second hand Danfoss NL11F to do some experimenting. If I blow it, so be it.

Now, here is my theory: I can use R507 in a R134a compressor under the following conditions:
- The oil must be compatible with R507
- Low side and high side pressures must be within the original limits
- Discharge temperature must be low enough.

The oil should be compatible since the same oil is used by Danfoss for R404/R507 and R134a.

Allowable low side pressure for the NL11F is 0.84 bar to 2 bar (-30 °C evaporation .. -10 °C evaporation with R134a)
When these pressures are translated to R507 evaporation temperatures, it shows that the evaporation temperature should be within the -50 °C .. -30 °C range. In my application, this requirement is easy to fullfill.

High side pressure is a tougher story since the saturated condensing temperature must stay below 31 °C to fullfill the requirement. Tough, but a liquid-cooled condenser should be able to fullfill this requirement.

Since the compression ratio stays approximately the same and the vapour heat capacity of R134a and R507 does not differ significantly, I do not expect problems with very high discharge temperatures.

Thus, as far as I know there are no technical reasons why it should not work, but am I correct?

And what about safety? I expect no troubles with safety, but I am not 100% sure.