|"Charge View" by Johnson Controls|
Trane introduced split system units with “Charge-Assist” back in 2008 in their Xli line. These systems have pressure transducers and temperature thermistors which are used to operate the electronic expansion valves in the unit. The board can also use the input from these sensors to determine if the system charge is correct. An external “Charge Assist” solenoid can be controlled by the board to allow the unit to charge itself. On these units, the technician only sees a blinking LED on the unit control board.
Johnson Controls (York, Coleman, Luxaire) are now offering units with built in pressure and temperature monitors and a screen to display system pressures, liquid line temperature, suction line temperature, superheat, and subcooling. The system will also tell you if it is correctly charged. It is like having a digital gauge set built into the unit. The main point is that you can check the unit charge without attaching any gauges or temperature probes. That means you will not lose any refrigerant while checking the charge.
These examples represent only the very high end systems from a few different manufacturers, but I believe it shows the direction the industry is headed. Systems will have sensors and intelligent controls monitoring system operation. I am sure that as the technology matures, its cost will come down, making this technology attractive to other manufacturers and in more main line units. Another driving force will be the desire to insure actual equipment performance and efficiency match the design. The most efficient system available installed incorrectly may perform worse than the lowest builder grade equipment available. Designing intelligent controls into a system is a way to improve system installation and service by taking guesswork out of charging. With systems employing these intelligent controls you really have no excuse for leaving the unit improperly charged.