Just curious if any of you have much first hand experience changing from an R12 system to an R134a AC system? Looking for comments on just topping up the system with R134a on top of the R12 or does the system have to be completely vacuumed? Also once converted comments on how well it does. Also interested in if you run the same pressures as the R12 system or do different pressures work better.

 

I have done several, complete vacuum down, most I also drained what oil I could get out and refilled with a dual compatible oil ( sorry, don't remember which )

I started out at 70 percent fill of the R12 value and played with it from there, usually closer to 80 percent cools best.

I have also just vacuumed a system down, refilled at 80 percent and had it work just fine.......( did that on free jobs.....)

 

Ive changed out several without the vacuum, no problem. You could just throw some freeze12 in and go if it just needs a simple recharge.

 

I have done a bunch. It works best if you flush the lines out to get the R12 oil out of the system after you vaccum the refrigerant out. Don't worry about changing the compressor oil. You have to change oil becuase the R134a will not pick up the R12 oil and carry it through the system. A little extra oil in the compressor that will not go anywhere is no worries. Take the weight of the R12 fill and divide it by 1.2. That will give you an 80% fill. Will an R134 system cool as good as R12, Noop, not gonna happen. It will do good, but not as good as R12. The pressures are very close to being the same, they are just a little lower.

 

All good info guys. It is good to hear I am not having to worry about changing a lot of parts.

What can I expect to pay to have the system evac and refilled?

 

I did my jeep year ago. It'll work if done right but it'll still never be as good as new

 

IIRC the condenser is the big difference in the R12 and R134a systems as far as cooling. You could replace the condenser to one for 134a while you're there and it will cool better.
I could be wrong cuz it has been a few years (about 12) since I worked on retrofitting A/C systems

 

Don't blend the refrigerants!

Together, R12 plus R134a creates what is called a high pressure azeotrope..
This generates a higher pressure blend than either of the individual refrigerants by itself.
This causes high head pressure and wacky cooling performance depending on what the ratio is...

At least pull a good vacuum and refill with pure R134a.

Considering the oil debate... Suffice to say there were a BUNCH of lubrication studies done on R134a in a variety of situations with different types of oils before they released that stuff to the public via the OEM's. There was a good reason that the R12 mineral oils failed because the R134a does NOT mix with them.. (like oil and water)
My R12 A/C's I've converted to R134a, I changed to POE oils after removing as much mineral oil I could.

My personal feeling on the R134a oils is the Auto Mfr's cheaped-out and chose to use PAG oils which are SO hygroscopic instead of using the more expensive POE oils.

What can you expect to pay to have it done? LOTS!
They charge an arm-and-a-leg for any A/C work...
You can buy a good set of R134a Gauges AND a brand new vacuum pump for what they charge to replace a major component!

 

Much cheaper if you have a "Harbor Freight" nearby.
But yes make sure you drain as much of the oil out as you can. I removed my compressor and turned it so it would drain out.
Now the environuts will scream at me but I gave mine a good charge of oil & 134 and then evacuated the system. (Of course I used a recover machine!!)
I then pulled a second vacuum replenished the oil and gave it a charge.
This was on a little Toyota Corolla so the cabin area is small but you can hang meat in that car!!!

 

Do as stated previously, the only other thing I would do would be to change out the receiver/dryer. It's only about 60 bucks,,, cheap insurance.

 

Again all good information guys. I will go to Harbor Freight to see what the pump and gauges are going for and then check on the dryer/receiver cost.

BTW this is for an 1982 Honda Prelude that I purchased new back when I was just getting out of the Navy.

 

Wow, had that a long time. I liked those cars. You better look for dry/age related rot on any of the lines. I would also buy new o-ring seals for all the joints and have them on standby in case it does not hold vacuum. I like to hold vacuum for a minimum of a half hour, preferably and hour. it helps boil out any moisture collected in the system.

 

Don't forget to add some UV dye when you're adding oil.
Cheap&easy way to find leaks with a UV lamp.
Especially those leaks that are blown away by fans!