Auto Air Conditioning & Heater Repair: r12-134 conversion, oil charge, older cars

Question
QUESTION: I want to use 134 in my 94 Honda Accord. I have gotten conflicting reports on the need to evacuate the old oil.  They have kits for this some of which have an oil charge that say nothing about removing old oil. I've been told by a couple of people they just added the 134 without changing the oil or using one of the kits that contain what I assume is something to make 134 compatible with the old r12 oil. Is there an additive you can recommend to allow the old oil to remain?

ANSWER: The topic of 'what oil to use' comes down to two physical properties.  Miscibility and solubility.  
 R134A Pag and Poe oils are not miscible with R12 mineral oils.  They can also react with the chlorides in the system from using R12 adn quickly breakdown the oils to a point they are less as useful than the orignial mineral oil.
 Also, in order to remove oil you must flush all the components.  R12 seals are not compatible with the PAG/POE oils or vice versa.

 For older cars that have lost a charge and are still R12 systems I have found just recovering residual refrigerant, changing fittings, vacuuming for one hour and charging 80 percent volume with a tracer dye that has PAG oil in it already is more than acceptable.  I have car still working on this method I did 6 or 7 years ago.

Wayne


---------- FOLLOW-UP ----------

QUESTION: I'm not clear on what you mean by charging 80% volume with the Pag oil and tracer.  Does vacuuming for an hour remove the old mineral oil? How much pag oil should be added?  
I suppose if the 134 is hard on the seals it might be best to bite the bullet and pay for r12 as long as the leak is minor and maybe the compressor will die before eating too much r12 ya think?
Thanks for the prompt reply.

Answer
Hi,

 Sorry, this might be more clear...


Charge 80 percent of original volume.  Lets say the system holds one pound of refrigerant.  You would put 80 percent of a charge into it which would be .8 X 16oz = 12.8 oz of refrigerant.  R134A has different properties than R12.

Vacuming it is bringing the system down to 29" of vacuum for about an hour (.5 hours in most guides).  This will cause any moisture in the system to be boiled off.

Add 2oz of PAO 68 universal automotive AC lubrican with a UV dye in it.  This can help you find small leaks with a UV light.