Does anyone have a rough estimate on how much it would cost to go from R-12 to R-134a?

 

done properly, you flush all the old mineral oil out of the system, then replace the dryer/reciever and nozzle, then evacuating and recharging with R134a and the suitable amount of PAG or Ester oil . depending on the year and model, it may or may not work that great, systems designed for R134a tend to have a larger evaporator and condensor as its not quite as efficient as R12 was.

 

Any estimate on cost to do it at home vs professional (where would I go to get it done?)
I have an 87 244 if it helps

 

Hard to say, lots of horror stories of this project going way over budget and not working in the end or lasting for a couple of weeks, then no A/C again!

Much depends on the condition of your system now. Does it work with the R12? if it does, why change it over? If it doesn't work now, what's the issue, bad compressor, leaks? All those will have to be remedied, change the seals, evacuate the system, put new oil, charge the A/C with R134.

If your system is OK, no leaks, compressor working and you want to go real cheap, you can charge the system yourself with Envirosafe, Frostycool, or similar and be OK. If you go to a shop and say fix the A/C, you may be looking at a big bill; these cars are getting old and few know or care about servicing them. Still, A/C shops will do it but hard to be sure about the result, it's all about the $.

 

When the factory conversion kit was available it included oil, a double layer high side hose, expansion valve, evaporator, receiver drier, and fittings. Something about the 134 molecules are smaller and tended to leak from the original hose (they were bad even with r12). The new evaporator design had better heat transfer. On a 240 ac system the fan sucks air through the evaporator. All newer volvos and most other cars have a more efficient blow through system.

As others have mentioned a converted to 134 system in an pre 1991 240 does not cool as well as a r12 system. We would install an electric fan on the front of the condenser to help - but even then they were about 5 degrees warmer, even after adjusting or replacing the heater valve. Another bad design - there are no blend doors, air is sucked through the ac evaporator and the heater core all the time. R134 also has slightly higher pressures - that will put additional strain on those 33 year old parts. Many times I had the low side hose explode when finishing one of those conversions - they get baked where they are near the exhaust manifold.

 

indeed, the AC worked far better on our 1992 740 than it ever did on the 87 240, both were R134 converted with the factory kits when relatively new.

In 1992, the 740/940s got a larger radiator, larger condensor, and dual speed electric fan, and the old mechanical fan was deleted.

the 240 worked so poorly that when I replaced the radiator, I ended up removing the condenser, AC plumbing, and compressor entirely, but we live on the Monterey Bay where temps are usually in the 70s and rarely above the 80s