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SCS charging methods

I have read other threads about different thoughts about charging an SCS basement unit. Of course this doesn't need to be done unless you break into the system or have a leak. 

Method one is to charge to the weight listed on the literature. That would be 36 ounces R 22

Method two is to charge to the amperage curve listed in the SCS literature. Rheavn was kind enough to post the literature on the forum.

Now that I have been into the innards of my SCS unit to replace a compressor, I believe there is a third way, and perhaps the best way to charge the system. The system is designed with a thermal expansion valve in each loop. In today's world of high efficiency AC units most home AC's are now using thermal expansion valves (called TXV or TEV for short). The accepted practice today is to measure the supercool of the unit and charge to achieve the appropriate supercool. 

This method requires that the temperature of the line just before the TXV is accurately measured. That temperature is compared to the saturation temp of the refrigerant at the high side pressure. The difference is supercool. I set the unit up for 8 degrees of supercool. It is . blowing 60 degree air to the bedroom.  The reason I post this is that the charge weight used to achieve this result is not the listed charge weight, and the amperage is also different. So, none of the three methods agree. 

Not to be an AC lesson, but let me take a simplified explanation of supercool . Let's use water as the make believe refrigerant. If the system were open, most would agree water will boil at 212 degrees. If we close the system and raise the pressure, most would understand the boiling point goes up. That relationship between boiling point and pressure is know as the saturation temperature. 
Stay with me on this simple explanation. Let's say that the pressure on the high side of our water system is 15 psi (atmospheric pressure) so water would naturally boil at 212. But we measure the temperature of the water coming out of the compressor and it's actually 206 degrees. You would have 6 degrees of supercool. 

I go through all this because the old school method of simply looking at the gauges on a system with a TXV simply does not result in the optimal charge for that type of system. I have read the other posts and the dissatisfaction that folks have had with results. The good news is that any decently skilled AC tech should know how to charge a TXV system. Because the TXV automatically regulates the low side pressure, it makes it impossible to get the very best charge just by using gauges only. 

My purpose in the post was to arm you with the right question to ask if someone is working on your SCS unit. How many degrees of supercool is the unit running? 

Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )

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