What would happen if you added R134A to R12?

[Grizzly]

Further to Richard Ellison's question.
What would happen if you added R134a to a system charged with R12.
IE Topped up with R134a without realising that the system had not been "Retro Fitted" (remember that term guys?)
Surely if R134a is truly a "drop in" Nothing???
Grizzly

[nike123]

Don't forget that solubility of mineral oil in R134a is not good and that R134a is not "drop in" just because of that. They seem to coexist just fine, but, since mineral oil is not miscible with R-134a, you'll need to use a suitable oil.

Since you have some amount of R12 in system, that could work perfectly fine, but that depend on ratio of R12 in mixture.
And, as we know, you have mixture of unknown thermal properties to be able to properly measure and diagnose system.

[monkey spanners]

I have seen systems where this has happened and you would not be able to tell from the way it operated that it had a mixture of refrigerants. If there was little R12 left in the system you would get a milky looking refrigerant flow in the sight glass and as you know poor oil return.

When i used to do retrofits years ago we did a few backwards, that is to say changed the oil and refrigerant on the first visit (due to no R12 on the van) and then call back over the next few weeks to do three more oil changes with no problems.

Jon

[Shadab]

i ve charged R 134a in a Thermoking equiped airconditioned bus instead of R12, which has fouled condenser coil.. my observations are
1. good cooling without changing compressor oil
2. good circulation of oil
3. But starting the system, heavy flooding of liquid on compressor cylinders, crank case, while the compressor got to warm up