Thread: R134 conversion
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Old 04-01-2003, 10:45 PM
GregS GregS is offline
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Join Date: Apr 2000
Posts: 459
Do not add refregerant according to weight. Period. Go strictly with gauge pressures - this IS important. You can purchase a set of gauges from for around $50. When the compressor is running and the engine rpm is up around 1500-2000, you want the low side between 25 and 27psi. Don't go below 25psi, but get right down to it if you can. The high side will depend on the ambient air temperature (low side shouldn't). I can't remember exactly the high side pressure, but the ballpark is ambient temp. x 2.2. Generally you should be around 180psi to 190 psi, but remember that you will see both high and low side increase at idle (which is why you have to take the readings while someone brings up the rpm). At idle you may l see high side go to around 220psi.

I second the recommendation to use Nylog. This is highly recommended stuff - use it on all the o-rings and threads, and make sure to get the kind designed for 134a.

Again on the oil, talk to the guys at I'm pretty sure Ester is ONLY, ONLY supposed to be used if the system is completely new and free of old oil (whatever it may be). PAG is the conversion oil, but I know the Texaco stuff is supposed to be the best. You just need to check whether it is compatible with other oil.

Lastly, the evacuation (i.e. pulling a vaccum), is really important. Don't cut corners. You must get as much moisture out of the system as possible, which is what pulling a vacuum does. It also helps you check the system for leaks. 45 minutes is recommended at a minimum for a system the was just opened to do a repair. If the system was open for a long period of time, then you should pull it for maybe 1.5 hours. This is where your own pump is nice, because most shops probably won't pull the vacuum as long as they should.

8oz of oil is the right amount for a new system, but since you aren't flushing, and you may have some oil remaining in the hoses and condensor, you might want to cut out an ounce. Too much oil can reduce efficiency.

O.k., I've rambled on for long enough. I hope this helps. Ultimately, what I'm trying to stress is that it isn't that hard to fix the a/c systems on these cars to begin with, and as long as you are willing to do all this work, do yourself a favor, and get it right the first time around!

Lastly, be real careful installing the bolt that holds the manifold to the back of the compressor. This is an awkward job, and I nearly stripped the threads on my new compressor when I did it - ouch!

Good luck,

'84 300D, 173k
'90 300CE, 163k
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