The R-134 is definitely less effective, especially with the '85 (some '86) and older A/C's. Smaller evap, single evap fan, smaller condenser. If you were to upgrade to a larger parallel flow condenser (e.g. 16" x 22") you'd end up with about the same performance as with R-12. Going to R-134A you'll also need to flush the system to remove the mineral oil, and then use PAG or POE oil. The R-12 compressors (like Sanden SD510 or SD710) are not likely to last as long with the newer oils they're not designed for, and the poorer oil carrying capacity of R-134A vs R-12. 

At this point, as long as you can get recycled R-12, there really is no downside to keeping it R-12 (other than fewer A/C techs, and tougher supply chain for R-12). I'm in Phoenix, and did the R-134A conversion with a stock '85 style system (mine is a Jan 1986 model Westy and had the pre '86 system). Performance really sucked. I went through several upgrade iterations (condenser, compressor, TXV, etc.) until finally building a custom A/C cabinet, and installing an '87 up style system with the larger evap and dual evap fans (I added one as well, but that's another story). 

Keith Hughes
'86 Westy GenV (Marvin)
--------------------------------------------
On Thu, 4/6/17, Automatic digest processor <LISTSERV@GERRY.VANAGON.COM> wrote:

 Subject: vanagon Digest - 6 Apr 2017 (#2017-128)
 To: "Recipients of vanagon digests" <vanagon@GERRY.VANAGON.COM>
 Date: Thursday, April 6, 2017, 9:00 PM
 
 ----------------------------------------------------------------------
 
 Date:    Thu, 6 Apr 2017
 19:00:56 -0700
 From:    Remy <remster2@YAHOO.COM>
 Subject: <No subject given>
 
 I have an '85 Westfalia with Air
 Conditioning.   Which is best - stay with R=
 12 freon or switch to R134.  My
 mechanic thinks I should switch but have hea=
 rd R 134 is not as effective AND I live
 n Arizona.  Thanks I value your opin=
 ions .
 
 Remy
 
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 End of vanagon Digest - 6 Apr 2017
 (#2017-128)
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