Factory load of refrigerant

The way modern systems work is by evacuating and weighing in the correct refrigerant charge. To do this you need special equipment to recover the refrigerant. It really is the only way to ensure the system has the correct amount of refrigerant in it.

The problem with just adding refrigerant without knowing what is already in there means you could over charge the system and cause the compressor to prematurely fail which is really expensive.

The last point is the refrigerant that was in the system is either still there or has leaked out. If it leaked out.....you need to find the leak.

Using high/low pressures to determine the correct refrigerant levels went away with R12 and R22.

 

+1

What was said above but if you really want to try you can use a sub cooling method

Search for it here and on the internet ..it requires measuring temps and pressures in and out of the condenser ..need accurate temp probes and a good set of gauges



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I haven't tried using my subcooling tester on a car system (I just went and checked to see if my tester had 134 on it!). I use it on residential systems to evaluate how well the system is working after reloading a charge in the same way I use the gauges to ensure everything looks okay. If you reload a system and the gauges are fluttering or the pressures are really off......the system has a different problem than the refrigerant.

Same goes with subcooling. While you could use subcooling to look at the temperature differential and try to adjust for that.....it would be tricky not to get into an overcharge situation as you close in on the optimum threshold.

 

i have used this method on a r134a system with success - the only issue is getting a good reading on the lines in and out of condenser ( surrounding heat always threw me off).. sometimes you get lucky and a diag tool maybe able to read the pressure on the input or output pressure sensor ( if there is one, depends on application)..

 

Without questioning all of the above no one seems to have actually answered the question.

The manual for the 456GT shows 30psia low and 195psia high as pressures at 68 to 72 degrees F not sure if this applies to 456M but these are typical for a 134A system.