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Depending on how long you want the A/C runs or how well you want the job
done. In principle, yes, evacuating R-12 then charging R-134a is
the main thing to do, but consider these scenarios:
<br>1. The system is 15 to 20 years old. How much longer can these
rubber rings last? The ring probably costs $1 each from dealer.
Replacing every one you open adds no more than $10 for the total job.
How much extra time do you want to spend the NEXT time to replace these?
<br>2. R-134a molecule is smaller the R-12. It cannot circulate the
mineral oil (used in R-12 system) well and that is why ester or PAG oil
is used in R-134a. A compressor without oil dies pretty fast.
The mineral oil takes up space and it won't help cooling so it should be
sucked out as much as possible.
<br>3. If the dryer/accumulator is few years old, replace it while the
system is empty.
<blockquote TYPE=CITE>So, are you saying you didn't change out the valves
or the o-rings or any of
<br>those? just drained the R12 and charged R134a?
<p>I have an 87 300E
<br>> aprox 3/4 of the full charge stated on the R12 label.
<br>> did not change any switches on mine.
<br>> mine was an 84 300sd
<br>> the case, minus a few cans!