Ok, so basically if ambient temperature is 90F, Subcooling will be lower, like 15F?
What temperature is considered excessive subcooling? Below 10F?
What counts as excessive will vary with ambient temp, anything over 20F is a bit excessive. Low subcooling would be around 8F or so. You always need a bit of subcooling to prevent the refrigerant from flashing before it reaches the TXV.
May I ask where you or how you come up with the 8F superheat valve? (I am looking at the Low Pressure Gauge, and 32PSI is 0C for r134a.)
I see that 32psi is 37F vapor pressure for R134a, so 45-37=8F superheat. This is an estimate though, you need to measure the suction line to get the true refrigerant temperature coming from the evap. It will always be similar to the outlet duct temp, but can be a couple degrees lower sometimes.
What values/measurement telling you that I should add more refrigerant?
I am not sure you need to add any, not without checking the system performance at a higher ambient. The reason I think you might need a bit more at high ambient, is that your subcooling is a touch lower than I would expect, and your superheat is a touch low. It isn't enough to be sure, as these TXV and variable compressor speed systems need to be observed in actual conditions before adjusting the charge.
When you say power consumption, you mean the wattage the AC uses at max? Currently is around 1000-1050Watt, which is equate to around 76-80A. This is much lower than previously, as it runs in around 1200watt or 90amps.... I wonder if that is due to the excessive resistance of the burnt busbar.
Yes, monitoring compressor power is part of adjusting and troubleshooting most AC systems. Lower power consumption is very likely related to the repair, which is part of the reason a power/current monitoring is important. If we had a good baseline of compressor current (say from a factory spec manual for this system), we could have pinpointed the compressor right off as a problem.
I am not sure what you mean by "near its max rating at the temp".
The compressor is a constant speed type, the controller tries to maintain a specific rpm. As the ambient temperature increases, the high side pressure increases as well. High head pressure increases the compressor load and power consumption. Increasing the condensing temperature/pressure will improve system output in hot weather, but also increases compressor load, so you need to take compressor load into account if tuning a system for very hot weather. Since this is a TXV system it isn't as simple as an orifice/cap tube type, but its still doable.
Because this system has a decent sized accumulator, it is less sensitive to charge volume at lower ambient temperatures. The important thing at high temps is to have enough refrigerant to saturate the condenser to get the best heat rejection, within the compressors limits obviously. It isn't clear yet if you need to add refrigerant, so just use the system, and if hot weather performance (outlet duct temp) isn't up to spec, we can reassess.
