Automotive Air Conditioning Information Forum (Archives)
Using a smaller orifice tube for better cooling
joe1431 on 
Fri September 17, 2010 4:41 AM 
You know how people with old GM cars use a blue ford orifice tube in place of the white for better cooling with R134A? What if you kept a GM car on R12 but used a blue anyway. Would it cool better, or would it freeze up the system.
NickD on Fri September 17, 2010 5:17 AM
Primary purpose is to reduce cycling at idle and you cannot squeeze in enough R-134a without exceeding the high side pressure to get reasonable high enough low side pressures. Also to keep the service AC light off on ATC equipped vehicles without have to shunt thermistors to fool them into thinking the low side pressures are higher than what they really are. Another thing to do on cycling switch vehicles is to lower their switching temperatures.
In terms of increased cooling, well kind of, at low engine speeds, keeping the low side pressure high keeps the damned compressor from shutting off. Really no cooling at all if the compressor isn't running. But has a very negative effect at higher engine speeds, the higher the low side pressures, especially at hotter ambients substantially reduces the cooling.
This is what happens when playing with the low side, other means is to reduce the high side pressures with a parallel flow condenser and/or better cooling fans so you can put in more refrigerant to increase the low side pressure so the compressor won't cycle as much. This would also help with an R-12 system. But reducing the size of the orifice in an R-12 system will decrease cooling.
Ideally maintaining a low side pressure of about 28 psi over the entire temperature and engine speed range would be the most ideal, impossible in any CCOT system. And to do this without constantly switching the compressor on and off that by the way, really wears the compressor and compressor drive train out. Like driving your vehicle accelerating from 0 to 60 mph in a fraction of a second constantly.
We've updated our forums!
Click here to visit the new forum
Copyright © 2016 Arizona Mobile Air Inc.