New A/C compressor R-12 to R-134 Ideas?

alamostation · 05-25-2007, 07:12 AM

I bought my 87 MR2 with a siezed A/C compressor and just bought a rebuilt one along with a receiver/dryer. I've worked on lots of cars before, but never on A/C. For starters, I don't know if I still have the R-12 in the system. Before I spend money to have it removed, how do I tell if it is still there?

Next question. I have access to gages and maybe a vacuum pump. How do you flush the system to get rid of the old oil? Every thing I have read says to do it, it just doesn't say how.

Lastly, do I really need to replace all the o-rings throughout the system? Some people say yes some say no. I would love to hear from anyone who has experience either way.

TomsMR2 · 05-25-2007, 10:09 AM

if you replaced the compressor, you dont have any refrigerant in it anymore. its a gas that boils at something like -22 degrees. once that system is open, your refrigerant is gone!

you flush it with AC system flush and compressed air. you'll have to disconnect your compressor and drier. if you vacuum from the high side it'll suck a LOT of oil out too, but dont count on only doing that. the flush is a bottle of fluid that you literally pour into your lines and blow through with air. just make SURE you disconnect the drier! it'll screw that thing up fast.

the problem with your current o-rings is two fold.. first, they're not R134 compatable.. second, they're so old by now that they probably wouldnt even seal. i picked up 250 new o-rings for like 10 bucks, it doesnt make sense to not replace them! also the replacement gives you a chance to go over all the fittings and double check them. you might want to consider replacing the expansion valve too, its a 3 dollar part and really either makes or breaks your system in terms of cold air output.

im on my second 134a retrofit, both work great!

emar2 · 05-25-2007, 06:35 PM

To see if there is any freon left in the system find the access ports on the front bulkhead. They are like tire valve stems, so just press one down to see if you get a release of gas. Do not have your face directly over the valve when you do this

. If you get nothing, then the system is already empty. I am an HVAC tech, andd in my opinion you are asking for headaches if you take apart a non leaking system. The main difference between R-12 and 134A as it pertains to the o-rings in the lubricating oil used in the systems. The oil used for 134A is a synthetic that damages the R-12 O-rings, which were designed for mineral based oil. The R-134A conversion kit includes oil that is both non-reactive to the R-134A as well as the R-12 O-rings. If you properly flush the system, you should have no problems. If you can put a vacuum to -30 mmHg on your system and it holds for 30 minutes with the pump turned off, you have no leaks. The rubber in the O-rings on the car are not exposed to air or sunlight, only freon and oil they last a really long time unless the fitting has been opened. Definitely replace the orifice tube and drier when you do the compressor. You will void any warranty if you don't and they are likely clogged with debris from the old compressor failure. Sorry for the long post, but I hope this helps and good luck.

05-25-2007, 07:12 AM	#1 (permalink)
alamostation Benevelent Mad Scientist Join Date: Apr 2007 Posts: 16 Thanks: 3 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	New A/C compressor R-12 to R-134 Ideas? I bought my 87 MR2 with a siezed A/C compressor and just bought a rebuilt one along with a receiver/dryer. I've worked on lots of cars before, but never on A/C. For starters, I don't know if I still have the R-12 in the system. Before I spend money to have it removed, how do I tell if it is still there? Next question. I have access to gages and maybe a vacuum pump. How do you flush the system to get rid of the old oil? Every thing I have read says to do it, it just doesn't say how. Lastly, do I really need to replace all the o-rings throughout the system? Some people say yes some say no. I would love to hear from anyone who has experience either way.

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05-25-2007, 10:09 AM	#2 (permalink)
TomsMR2 Formerly Tom Brokaw Join Date: Feb 2005 Location: Bay Area Posts: 2,497 Thanks: 8 Thanked 233 Times in 168 Posts Blog Entries: 1 iTrader Rating: (0/0% )	if you replaced the compressor, you dont have any refrigerant in it anymore. its a gas that boils at something like -22 degrees. once that system is open, your refrigerant is gone! you flush it with AC system flush and compressed air. you'll have to disconnect your compressor and drier. if you vacuum from the high side it'll suck a LOT of oil out too, but dont count on only doing that. the flush is a bottle of fluid that you literally pour into your lines and blow through with air. just make SURE you disconnect the drier! it'll screw that thing up fast. the problem with your current o-rings is two fold.. first, they're not R134 compatable.. second, they're so old by now that they probably wouldnt even seal. i picked up 250 new o-rings for like 10 bucks, it doesnt make sense to not replace them! also the replacement gives you a chance to go over all the fittings and double check them. you might want to consider replacing the expansion valve too, its a 3 dollar part and really either makes or breaks your system in terms of cold air output. im on my second 134a retrofit, both work great!

05-25-2007, 06:35 PM	#3 (permalink)
emar2 '87 NA T-bar; '88 FX-16 Join Date: May 2007 Location: Phoenix AZ Posts: 13 Thanks: 0 Thanked 1 Time in 1 Post iTrader Rating: (0/0% )	To see if there is any freon left in the system find the access ports on the front bulkhead. They are like tire valve stems, so just press one down to see if you get a release of gas. Do not have your face directly over the valve when you do this . If you get nothing, then the system is already empty. I am an HVAC tech, andd in my opinion you are asking for headaches if you take apart a non leaking system. The main difference between R-12 and 134A as it pertains to the o-rings in the lubricating oil used in the systems. The oil used for 134A is a synthetic that damages the R-12 O-rings, which were designed for mineral based oil. The R-134A conversion kit includes oil that is both non-reactive to the R-134A as well as the R-12 O-rings. If you properly flush the system, you should have no problems. If you can put a vacuum to -30 mmHg on your system and it holds for 30 minutes with the pump turned off, you have no leaks. The rubber in the O-rings on the car are not exposed to air or sunlight, only freon and oil they last a really long time unless the fitting has been opened. Definitely replace the orifice tube and drier when you do the compressor. You will void any warranty if you don't and they are likely clogged with debris from the old compressor failure. Sorry for the long post, but I hope this helps and good luck.