| I been researching on my cars AC system and being that I have a huge FMIC (4" thick) I tend to try and keep the car as cool as possible. With a 90-93 models we have an R12 system vs a R134a system component wise they are similar. First read this training guide its is the best source of information I have found so far, next to AliaZ emails (which I have been bugging him a lot.. Thanks Don) has given me a good education. Ariazone Training Manual for Automotive AC systems I like to make some cliff notes
- IF you have an R12 stay R12 (yes its expensive per pound vs 134a s but works better and is a lot less work), FYI I found 40lbs of R12 at $1,200 (so yes it is available and if you pass your epa test you can buy it.. [ http://epatest.com/609/openbook/ ])
- Freeze 12 if available also works If you have to switch to R134a (because your AC compressor failed or etc). Be aware of the following
1. R134a runs at higher pressures than R12. At 85 degree F you will see 45-55 low and 225-250 high for 134a for R12 you will see only 35-45 low and 180-220 high.
2. Vent temps are 15% higher .. if you normally saw 40 degrees out of a vent you will now see 47 degrees.
3. R12 condenser is a serpentine type core a parallel flow is used on an R134a and is 25% more efficient.
4. R12 Evaporator is a serpentine type core a parallel flow is used on an R134a and is 20% more efficient.
5. Replace all black o-rings from an r12 to the green o-rings used in R134a.
6. R134a uses PAG46 for our cars, however PAG46 and mineral oil in our cars does not mix, you must flush out all old oil out of system. However my research shows me to believe that PAO oil is a better solution as it is not hygroscopic (does not pull moisture from air) will help from having evaps or condensers from freezing up. Others believe that POE oil is a good solution as well its hygroscopic so i am not sure. Here is a good article to read.
http://www.behrhellaservice.com/behrhellaservice-com-en/assets/media/TM13_Oelflyer_GB_J00583.pdf 7. R134a uses approx 80% less refrigerant than R12 24oz of R134a is a good amount. FSM shows 1.65 to 1.87 lbs of R12 Please understand that I am no true expert on this matter and I am just sharing my findings and my conclusions to help the community, thus please note any corrections that are needed.
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