REFRIGERENT r12 or r134
In our second part of the Mercedes 450SL air conditioning restoration, we will focus on prepping the system for freon.
The 1975 450SL I am restoring, had the original compressor with r12 refrigerant. While it had long since leaked down over the near decade of sitting, the old r12 compatible oil still remains in the system, and that MUST be removed before changing over to r134. As mentioned in part 1 of “Chill Out” a remanufactured Mercedes A-6 compressor was purchased in place of rebuilding the original unit. The original units were steel, painted black and were easily recognized by the built in oil sump or “belly” at the bottom of the unit. The new “A-6” is known as the Pro6Ten.
MAKING THE SWITCH
Before we get too carried away, there is no urgency to switch from r12 to R134 unless you have major work to do or simply wish to do so. The major advantage of converting is the cost to recharge a system with r12. Brief research shows a 30lb. bottle of r12 is retailing on eBay for around $450, while r134 is retailing for $125.
If you are however going to make the switch from r12 to r134 on your old model A-6 compressor, it is critical to do the following according to SMP Temperature Control Division / Four Seasons®.
THIS IS FOR ORIGINAL FRIDGEDAIR/GM MODEL A-6 COMPRESSORS ONLY
- Completely empty A-6 compressor of all old mineral oil by removing oil filler plug
- Refill compressor with oil prior to installing
- Refill only the compressor with 11oz. of PAG-Oil/150 ONLY!. Do not let the system sit open
any longer then absolutely necessary, as the system will take on moisture. Do not divide the
oil throughout the system as is common among other A/C systems. - Replace the receiver dryer
- Replace any old lines or fittings
- Flush condenser and evaporator with appropriate chemicals to remove as much excess
mineral oil from the r12 system as possible. R12 mineral oil does not mix with PAG-Oil, but I
was told that any residual mineral oil will “park” in the system, not effecting performance. - It is also recommend that a professional A/C technician perform the change over from r12 to
r134.
Be sure to call SMP Temperature Control Division/Four Seasons at: 1.888.252 8344 if you have any questions on your A-6 compressor or speak with a qualified A/C tech.
It should also be noted that a remanufactured compressor from Four Seasons has been pre charged with 3oz. of PAG-Oil/150. The tech at SMP however did recommend that the existing oil be drained through the oil filler plug, measured and returned to the unit with the new. This process will guarantee that a full 11oz. of oil are in the compressor prior to operating.
Remember, DO NOT operate your compressor until the system as been completely vacuumed down, filled with the appropriate oil and completely charged with r134 or r12. Sever damage to the compressor can result if the system is not properly prepared.
The photo shows the original labeling on my 1975 450SL A-6 compressor which was in surprisingly good condition. Perhaps being caked with a 1/4 in. of grease and road grime preserved it. To keep the look of this car as close to original as possible, I will be making a reproduction of this sticker for the new compressor. While not very visible from the top down when installed, it is partly visible, hence the replacement sticker. It would be important however should the car be sold, for the new owner to be informed that the system was converted to r134 and the compressor sticker is simply a restorative element.
