You might consider about the upgrade(?) to r-124 and the problems with some Fiero compressors. The compressor on the 3.4 will probably handle R-124 with no problem. Some Fieros don't play well with 124 and r-12 is not exactly a wal-mart item anymore.
If you do the upgrade, there was a good post here a while back on the trials and tribulations on 124. It should be in the archive somewhere.
Here is some stuff I clipped on the 124/12 problem. I don't have the original poster so I hope whoever posted it first will forgive my lack of credit:
R-134a is not a direct drop-in replacement for R-12, but it comes pretty close. In fact, some DIY retrofit kits that are being sold in retail auto parts stores treat it as if it were a drop-in replacement. These kits include a can of POE oil, some adapters and thatís all. Though few modifications are required on most late-model A/C systems, that isnít necessarily true for all retrofits.
Some compressors have viton seals that are not compatible with R-134a. These include Tecumseh HR980, some Keihin compressors and some Panasonic rotary valve-style compressors. Others are not rugged enough to handle the higher pressures that are created by R-134a. These include Harrison DA6 (mid-1980s GM applications), which can be replaced with HD-6, HR-6 or HR-6HE compressors and Ford FX-15 compressors, which can be replaced with an FS-10 compressor. Try to convert one of these applications the "easy way" and youíll doom the compressor to failure.
On some vehicles, compressor replacement is required when retrofitting. These include V5 compressors on 1988-89 models with a date code between 1/88 and 8/89 and a royal-blue label, all DA6 compressors and R4 compressors with a date code between 1/1/90 and 6/18/93.Ē Source for all the above: http://www.babcox.com/editorial/us/us29928.htm
Fieros with DA6 compressors are not candidates for conversion to R134a. That includes all 1984-1985 models and 1986-1987 models with 2.8L engines. Also, most 1988 L4's with original V5 compressors should not be converted. Best bet for the DA6/88-V5 owners is to stick with R12 till the compressor fails, then replace with the a newer compressor type and convert to R134a. If all the R12 leaks out and the DA6/88-V5 compressor is still O.K., conversion to one of the alternate refrigerants (Autofrost, FRIGC (FR-12), Freeze 12 or FreeZone) may make sense. The alternates operate at lower pressures and may allow the weaker compressors to last another year or two. But as jstricker says, the service port fittings must be changed (each alternate type has unique fittings) and most service shops arenít set up to handle the alternates.
Hope this helps,
88 GT V6 Crazed-Alligator white
DIY Leather Interior Available
Shipping weight..1200-1500 lbs. Freeze-dry specials!!!
[This message has been edited by TennT (edited 12-19-2003).]