R-134a vs. R-12
I won't attempt to fool you and say the following excerpt is not a plug for our products, rather consider it as a starting point to help you stay cool this season. And remember, no one (including me) is an "expert", we are all learn everyday:
This past summer I completed a conversion of the air conditioning compressor on our 1984 928s, replacing the Nippondenso 6E171 with our Sanden Kit. The Sanden has proven to provide smoother operation, without any noticeable load on the engine, as well it has sufficient capacity for the total system and is extremely reliable.
During the course of the replacement of the compressor we had a choice to either switch R134a or remain with R12. As a result of much research and debate within the refrigerant community we decided to keep the system "R12". Though conversion to R134a is very simple, we find R12 to provide better heat exchange potential during times when air movement across the condenser (heat exchanger) is nominal ... such as at idle or slow speeds; The benefit for example felt most when you are stuck in city traffic on a hot
This is not to say it is not cost efficient or worthwhile to convert to R134a in such cases when you are overhauling the system (i.e.. Replacing the compressor or completely recharging the system).
The basic requirements for the R134a conversion require:
PRE-TESTING THE SYSTEM
to locate leaks prior to replacing refrigerant.
REPLACING THE OIL WITH R134a
compatible oil. Here the debate continues on whether you should use a PAG or Ester formulation. Both have their pro's and con's and typically specific compressor manufacturer's have chosen one over the other. In our retrofits for R134a we prefer Castrol Retro A/C oil as it absorbs less moisture, it's compatible with most seal materials and hoses and it "gets along" with and residual R12 oil left in the system. How do you remove the old R12 oil from the system. Simply, without being neurotic about the details, you replace you receiver dryer with a new receiver dryer who's desiccant (moisture absorbing material) is rated to XH7 (most common for automotive industry). The receiver dryer retains a fair amount of oil so this is one of the reasons to replace the old one in addition to replenishing it's moisture absorption capability. Next you need to remove as much oil from the old compressor (if you intend to continue using it, or not rebuild it) by disconnecting the high side and low side lines and turning it over so the oil can drain out. If your compressor has a drain plug then this should be opened as well. Allow the compressor to drain for several minutes and turn it over several times to allow the oil to move from it's inner chambers. You will not remove "all" the oil from the compressor but you will most likely remove a sufficient quantity such that it will not conflict with R134a.
Do you need to remove the condenser, evaporator or hard metal lines of the system? Not really. If your system has sat idle (not running) a day or so then most of the oil will move to it's lowest points on the system. It is preferred to "liquid flush" the system according to most. Liquid flushing attempts to flush away old oil and contaminants from the system using an approved flushing agent, under pressure, running through a closed loop with a filter. Do not attempt to "pour" a solvent down a hose line and blow it out with shop air, it does not work and can make for a dangerous situation. If your shop expert never heard
of liquid flushing, if he does not have the approved equipment, or if he never heard of MACS, then look around for a qualified/experienced shop to work with you. Reference: SAE J1661 - Retrofit procedures for all proper details and procedures.
REPLACING RUBBER HOSE LINES
is preferred for two keys reasons. First you must remember the "age" of the car. If you have an 1987 or older model year then your rubber AC lines are now over 12 years old! You most likely have replaced a few hot water coolant lines by now if you are prudent, and it does not make sense to have the system charged hoping they won't leak slowly over the season. Second, with the introduction of R134a came "barrier" hose line. Basically a hose within a hose that limits the probability that smaller R134a or even R12 molecules will slowly escape through the hose wall over time (why are you topping off the refrigerant every other year).
Fortunately most of the 928 sharks' AC line system is made of metal! The key items that are not metal are the high pressure line running from the the condenser to the compressor and the low pressure line running from the compressor back to the passenger side fender wall. We designed and replaced both lines using our barrier hose during our conversion to the Sanden compressor system. Their replacement is easy, though I will admit if you try to rush the job and not determine where the high pressure line enters the front wall, it will prove to be a challenge. We have since designed hose sets for both the original Nippon 6E171 and the Sanden, complete with R134a compatible orings of HNBR material. Thankfully our system won't have the potential to leak from these two hoses and we are R134a ready at any time!
REPLACING SERVICE PORT VALVES
is very easy. Two adapters screw onto the old high side and low side R12 fittings.
Reference SAE J1660.
OTHER THINGS TO PONDER
before you attempt to retrofit to R134a, is the condition of your current compressors o-rings and seals. Orings that seal the case half's, nose and rear compressor have been under a somewhat static load for some time, they are prone to failure over time and typically may not provide a good seal if their condition is poor when R134a is introduced. PAG type oils are not recommended in such cases, this is why we choose Castrol's product. It would be considered "smart" in any situation to have your compressor overhauled, replacing the old orings and seal with R134a compatible material. Remember... before you attempt to retrofit, if your system has refrigerant in it you'll need to have it removed legally! Read up on who can and cannot perform these operations at MAC's web site mentioned further on below.
is placed over current R12 info on the car to make users aware of the change to R134a
Reference: SAE J1661
with R134a in the 928 shark have been good from what we know. We have sold remanufactured Nippon compressors as well as new Sanden kits, both R134a ready to go and all results seem to indicate that everything went smoothly and performance with R134a was acceptable. You must understand that one key reason that R134a works well in the 928 shark is because of the extremely large condenser that was incorporated in the car. Smart design work on behalf of the engineers at P.
about keeping your shark's ac system running cool and what you can do and can't do with respect to EPA regulated refrigerants by contacting MAC's (mobile air conditioning society), in PA at 610-352-4600 or visit our web site and go to our links section.
Stay cool and have fun this season.
PS. cell phones are not allowed on the golf course.
references: MAC's "Guidelines for Automotive Air Conditioning Retrofit
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