My 85 300d has r134 fitting on the high and low side of the AC. Was R134 factory or retrofitted during that year? I cannot find a label indicating R134 or r12. Any ideas?

85 300d 192k

R12 was original. Changed to R134.

R134A wasn't used until the mid-90's.

If it has that 134 fitting them someone put that on....and we assume put 134 into it... that is the ' indicator' that you should not put R12 into it... you would have to really work to do that ( which would screw up other things in the process by mixing them ) since you would have to violate the sorta fail safe system in place having to do with can tops, service fill lines, etc...
You can have it checked if you suspect something is mixed up. Some shops will have this sort of equipment :
http://austin.craigslist.org/tls/919362073.html

The system was obviously converted. The vast majority of conversions never see the label in spite of the fact that it is required by law.

Reverse convert to R12, by thoroughly flushing all components, including flushing the compressor with refrigeration oil, dry everything thoroughly, add the proper amount of refrigeration oil distributed around in the various components. Once the system is put back together, turn the compressor a number of times by hand before evacuating and starting up. Recharge with R12 and you will then have a proper system.

" by thoroughly flushing all components "
Some can not be flushed... the Receiver/dryer and the manifold on the compressor for instance ... the evaporator is tricky and different opinions exist about the ability to flush it well.

' dry everything thoroughly '
when flushing use dry nitrogen gas to push the liquid flush through the components.

then when the parts are put back together use of a good vacuum pump for long enough to ensure dryness is critical to not having acids form inside the system which will attack the critical working passages of the system.

to flush you must take apart the system ... so when putting it back together use the correct NEW O-rings ( check the color ) AND use the correct Nylog color to wet them ( this is condensed refrigeration oil which matches your working oil )... use two "line" wrenches to tighten connections to keep from bending them.

the compressor is not power flushed the way the rest of the system is.. this hand turning Larry mentioned is used for the flushing ( off the car ) and then again before start up to get some oil into the compressor. This Delco compressor has no oil sump like other styles .. so it should not be started dry.. but should not be hydrolocked either... all the future lubrication will be by oil which is dissolved in the freon circulating through the system. ( it is called oil miscibility and is often overlooked in the equation when people try suggesting ' alternative' refrigerants ).. R12 has excellent capacity in that regard. So does R134a for its respective oil

Once the system is back together use the nitrogen to check for leaks ( in the pressurized mode ) before using the vacuum pump to both check for leaks in the vacuum mode and dry the system by lowering the pressure enough for any moisture to boil off. Deep pockets of oil, if contaminated with moisture can not be renewed by vacuuming. The receiver dryer should not be opened up and installed until the moment you are about to install it into the system.