Been considering converting the old knee knocker evaporator in my '66 F100 from an expansion valve system to orifice tube. The tubes are supposed to be more efficient and can be placed in other or easier locations then up under the dash like the expansion valve. Is it worth the effort or should I just keep it as is? I'm making all new hoses so retro fitting or breaking open the system isn't a problem as this will be a new install.
The fixed orifice system was designed to cost less to manufacture. It is by no means a better system. It cycles the a/C clutch between 25 and 45 psi to maintain evaporator temperature. By using it with your system, you will shock load your compressor and send it to an early death. An expansion valve system is more costly but won't shock load your compressor. If you choose to use a fixed orifice system, then convert to a rotary compressor like a Sandon. Even with the Sandon style, it will eventually kill the compressor, just slower. The good thing about an expansion valve system is the fact that the valve will modulate flow into the evaporator and not cycle the compressor. The bad parts are accessibility and cost of replacement. But, when it's all said and done, it is still a better way to control evaporator temperature. I have worked on both systems for way too many years and have seen the good and bad of both systems. When the fixed orifice tube came along, we saw an increase in compressor replacements. I worked with the Ford a/C definition program for several years and made field reports to the engineers in Dearborn. Off the record, they all told me why the new system was used and wished they still used the TXV system for dependability. You can use a Sandon style compressor with the TXV system to get less vibrations and lighter bracketry.
Thanks for the reply Deuce, and I am running a brand new Sanden 508 compressor. I've been reading up on the pros and cons of the two or really 3 different systems if you count the variable orifice and the fixed orifice tubes as compared to the TXV. Seems the biggest gripe about the TXV was accessibility since on most indash systems the valve was hard to access. Mine being a hang down evap the accessibility issue is not much really. I'm ***uming that if I go with the TXV that I will need to buy one that is sized/calibrated for the 134? I've got a brand new one thats on an R12 hang on unit that has never been charged that I could use if it would work.
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