Assuming I can get R-12 what other tools are needed to fill the system with R-12 referigent. I now it is low because it has not been used for a year or more.
I would like to do the service my self. What is envolved?

what kind of modification do I have to make to use R-134, thought I rather not?

Bob Geco
1992 300-E M103 983 motor

First of all are you sure it's R12? My 92 400E is R134 from the factory. It makes a difference in the answer.

Yea both my '92 500Es had R134. Check the charging ports. If they look like tire valves then it's R12.

Special tools: Set of manifold gauges with R12 adapters - Ebay is a good starting point. Vacuum pump (electric motor driven). R12 can puncturer and valve.

If all R12 is gone, you need to find the leak or recharging is a waste of money. In which case you'll need a dye injector or use a can of R134 with dye.

You'll probably need a UV light source to see the dye clearly.

You should replace all accessible O-rings, the receiver/dryer, the pressure sensor on the receiver/dryer.

Any leaking hoses, condensor or the dreaded evaporator will need to be replaced. The compressor may need new seals or buy a remanufactured one if too far gone.

You may be lucky and find all you need to do is top off a low charge in which case the gauges and R12 can tap are all you need in addition to the R12.

Don't do this. If you do, and you want or need to get the system evacuated by a professional in the future, you'll incur him a hefty charge to get rid of the mixture in there. Of course, he'll pass that charge along to you.