The statement concerning the efficiency of 134a is not valid. Pound for pound 134a is more efficient that R12. 134a will transfer more BTU's than r12. The downside of 134a is the increase in high side pressures, and thus the refrigerant requires more efficient condensing. Lack of this extra condensing (retro fitting) decreases the thermal efficiency of the refrigerant. Because of the lack of adequate condensing of a standard r12 system and to control what many perceived as excessive high side pressures the practice of
short or undercharging the system became the norm. This practice had two adverse effects, first the system now lacks the proper charge for complete cooling performance and also lacks sufficient refrigerant to maintain proper compressor lubrication. Both of these issues are evident with the claim that '134a does not cool as well as r12' and the increase in compressor failures due to lack of lubrication migration.
When a r12 system was charged at 100% of OE r12 specifications and condensing was increase to accommodate the extra pressure/temperature of the new refrigerant we often experienced no change in cooling performance and in some instances a slight increase in cooling performance (cabin air temps). The practice of short charging came about for several reasons, primary an effort to control operational pressures of the system. For some unknown reason many feel that there is an 'acceptable' or 'I like this' operational pressure range of the system. Because 134a operates at approximately 25-35% increase in high side pressures, it became the 'norm' to adjust charge rate to accommodate this perceived high side pressure. For instance, assuming that an 'acceptable' high side pressure was 225 psi for an r12 system. Then the same system with 134a would operate at approximately 280 - 300 psi. Certain heat loads could actually see this increase over the 'unacceptable' 300 psi. So let's simply adjust charge rate to return pressures to an acceptable range. This effects two important issues, the reduction of refrigerant reduces the cooling efficiency of the system (severe undercharge) and the movement of lubricant. Both are detrimental to the overall performance of the system. The system is designed to operate with a specific amount of refrigerant and performs best at this level. A reduction of refrigerant level, either r12 or 134a will compromise cooling efficiency. A simple statement should be that as long as r12 is available to use r12...the system will function best. If retro fitting is desired....then accomplish the test completely. A simple condenser change to a more efficient condenser and a full charge of 134a will work very well. Flush the system to remove all residual mineral lubricant, keep in mind that residual lubricants become a contaminant to the system and occupy space within the system. This lubricant has no place in the 134a system and should be removed. A serious reduction of refrigerant is not a key to a successful retro.
All this being said, a suggestion would be to remain with r12 for your system. However, if the desire to change refrigerant is there....then by all means do so....but do it correctly and you should have have any cooling system problems. Completed a retro on a 85 Chevy 1/2 ton pickup last week. Evaporator flush, new orifice, new accumulator, new R4 compressor, new compressor/condenser/accumulator manifold, correct retro adapters (the brass ones with a true schrader valve ), new aftermarket 6mm pic condenser, 100% 134a recharge. The operational pressures mirrored those expected for r12 given the ambient temp, evap outlet temps were within 3 degrees of a OE 134a system (2006 GMC Sierra 1500). Vent temps were off a bit, app 5 degrees center. This could be contributed to loss of vent duct sealing, lack of cabin insulation between the vehicles etc.
However, the system worked, the compressor was quite (adequate lube flow) and the customer was extremely happy. The vehicle had been retro fitted at an earlier date and had several compressor installed (all lock up or were noisy----no lube). The owner 'loved' (his words) and wanted to keep it functioning. Did we go over board with the repair....some would think so.....but we have a satisfied customer, a good repair and a profitable invoice. DO IT ALL !!! DO IT RIGHT !!! DO IT ONCE !!!
Oh yes, this truck resides in Palm Beach county FL...hot and muggy.....often VERY HOT and VERY MUGGY!!!!
Good luck with your repair...either way you decide. Do not take short cuts....you will be rewarded for your efforts with a successful repair.
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