One day I was looking for r-22, like always source #1 is eBay. I found r-22a in results. I started looking for more info. I found big discussion on "hvac-talk". Nobody tried it but everybody "heard" from "body" scary story.... Everybody had his OPINION but nobody eve tried it, what a bunch of ....("professionals"). Finally I gathered some info, that made me think to try it.
I am still in process (nothing is done, waiting for parts). R-22a is a mix not just pure propane. I think it is great because everybody can legally play with AC using it (initially system must be properly evacuated). Even considering that most of laws that regulate refrigerants is pure BS we still have to follow them.
When one refrigerant is replaced with the other one many things must be redesigned in the system that was originally designed for original refrigerant.
One of this things must be metering device (MD). If it was cap tube, then it was designed for r22 r22a(propane as well) has completely different properties. Now cap tube will not work properly. The problem with cap tube is it is fixed it will not readjust itself. For this reason I will go only with TXV. TXV is more forgiving. It is like driving auto VS manual (auto will never forget to shift
)
The other problem with cap tube is DIY. Yes we don't have enough resources to run thousands of tests when we "design" our system. If you make mistake with heat load and over-under size condenser or evaporator cap tube will never let your system run properly.
R22 and r22a PT charts look really close, it means that TXV with r22 charge in its bulb might work OK and it will provide proper superheat.