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What pressure would you expect for R134A, R22, or R12 at those same conditions. Convert the pressure for those gasses to saturation temp, and use the same saturation temps on R404A systems.
 

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Discussion Starter · #8 ·
Made my life easier

Since I originally posted this thread I purchased an SMAN4 manifold with the built-in P/T charts and it's made my life much easier. I just punch up the refrigerant I'm working with and it automatically shows the saturation temps. More than that I can attach the included temperature clamps to the lines and get Superheat and Sub-cooling in real time. I also picked up the wireless remote temp probes and the HG3 so I can get a full system analysis and target Superheat. No more guesswork. I couldn't be more pleased with this setup and customers are impressed with the level of efficiency I can squeeze out of their systems.
 

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So referring to David40 original post to his 34 degree indoor and 80 degrees outdoor does not correlate 63/290 on the PT Chart? It would be more like 75/173 psi? Im just making sure Im doing this right so that I don't get confused.
 

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So referring to David40 original post to his 34 degree indoor and 80 degrees outdoor does not correlate 63/290 on the PT Chart? It would be more like 75/173 psi? Im just making sure Im doing this right so that I don't get confused.
In order to have the coolers temp at 34. While the system is running, the refrigerant temp in the evap would generally be at 24, so 32 suction pressure while running. The liquid line pressure would also need to be higher then the saturation temp of the outdoor ambient, so liquid line pressure would be at least 254. But 290 would not be out of line on some condensers, varying with location outside.
 

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Also to know is, what are normal operating pressures for r404a? When the temperature inside the freezer is at about 0°F, the low side pressure should be 8-10PSIG for R404A charged units. Refrigerators should pull down to 35°F in about 20 minutes when located in an ambient of about 75 °F.
 
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