R134a conversion

[KHE]

RE: Post #10 by KHE........

I agree with everything you indicated except for:

"Installing a lesser amount of R-134a than what is specified for R-12 is also incorrect - the lesser amount will constantly set the low refrigerant code and disable the compressor. The proper charge of R-134a is the same amount that was specified for R-12. In other words, if the system was spec'd for 2.0 lbs. of R-12, then the correct charge of R-134a is 2.0 lbs. This was confirmed by an HVAC engineer at GM Powertrain and relayed by the guru that used to frequent this board"

This info is not the recommended procedure from any professional HVAC person. 85% is the recommended charge of R134A to an R12 system and then proceed from that threshold. Doing otherwise is an unsafe procedure. I've done a lot of systems and never has a low-refrigerant code been set, nor has the compressor been disabled by the low-pressure switch once the pressures are correct.

I'm just reiterating the information that was conveyed by an HVAC Engineer who did conversion development on the Allante. On the conversions that you've done, have you measured the actual weight of R-134a added to the R-12 system? The total weight of the charge starting with 85% and then adding to achieve the pressures may be close to the R-12 spec. as we're only talking 4.8 oz on a 2.0 lb capacity system.