Yesterday I happened to catch one of those call-in car care programs on the radio.A lady wanted to know if she should pay $200 to have her Freon recharged or go with an R134a conversion for about the same price. The host told her he NEVER recommends the conversion because R134a operates at much higher "head" pressures and that it's bad for the engine and the radiator.

What is he talking about? The AC system is a sealed, separate system from the engine. So why would it harm the engine and radiator? Or di I misunderstand the answer? Anyone?

 

his ans. is loco

 

It harms the engine and radiator only in that the engine has to work harder at idle against a bigger load. The radiator would, in turn, be 'working' harder to offload more heat generated by the engine working harder. Most original condensers cannot pass enough heat at idle, so pressure raises.
The conversions end up running the compresser at a higher pressure than it was designed to handle. R134a just chemically/physically does not do the same thing as R12. It boils at lower pressure, 19-20psi for 32F vs 28-30 for R12. Has smaller molecules, etc etc etc. Just not the same thing.
Essentially, when you convert to R134a, you end up running a 'partially-charged' system to prevent the head pressure from blowing up the compresser. If you had a full charge, so that you fed the evaporator liquid-only, vs a liquid/gas bubble mixture, it would be performing as an original designed system, either R12 or R134. Both types were designed to get liquid to the evap - via Orifice/TXV or whatever. The converted system does not do that, and cannot if it is to remain in one piece. You end up with a bubbly mixture in a converted system. The condenser is not able to take all the heat out of the refrigerant, so some remains as bubbles...
A "good" conversion would entail the replacement of the condenser, in *most* cases with a parallel flow condenser, and the replacement of the accumulator/receiver-drier with equivalent using X-7 or X-9 dessicant. (The older dessicants seem to come apart with R134a.) AND the draining of the old lubricant (mineral oil) from the compresser and flushing as much as possible from the evap and condenser. Replace lube with ESTER or Texaco HFC100, evacuate for an hour or so, and recharge to 70% or normal R12 charge, and work up from there til you get the best cooling.
tom

 

What he said. I work on auto systems daily and I agree with the explanation. Also you would be doing the engine and radiator a favor by adding a high pressure cutoff to the compressor circuit. All the new models come that way.

 

Thanks, guys. I think I understand what he was talking about. I think I'll just have the R12 recharged in my car. The wifes Topaz has ALL the symptoms of "Black death." Probably have that one converted with a new condenser and compressor.