So, what happens if you don't have the correct orifice installed? Sure, you could attempt to adjust the Superheat to the target, but it will never reach the desired goal. If you did not know what the target should be, use this simple formula that most to all Superheat Charts are based on, using the Condenser Ambient Temperature and Return Air Wet Bulb (taken at the unit, not in the space).
Target Superheat Formula
|Low Superheat & Low Subcooling|
If you have an over-sized orifice, you will be overfeeding or flooding the evaporator. If you did not verify that there was some sort of reasonable subcooling value, than you would expect that the unit was overcharged based on the low superheat. Taking a look at the first picture of the digital gauges, you can see that the Superheat and Subcooling are both low, indicating that adjusting the charge will not only be impossible, but could cause the refrigerant to flash off prior to the metering device since the subcooling will also go down as refrigerant is removed. When charging to the proper Superheat, you should have at least 5F, but not more than 25F subcooling with a fixed metering device. This indicates the proper size orifice and that the refrigerant will remain a liquid until meeting the orifice.
|High Superheat & High Subcooling|
I guess the moral of the story here is to install the correct orifice for the condenser being installed, this way you can avoid this diagnosis from the start. As a technician, if it came time to verify the orifice size, I would take no chances and just install a TXV. I would hate to go through the process of pumping down the system, changing the orifice, vacuuming the system, and trying to adjust the charge just to find out that the new orifice was still an issue. Plus, by installing a TXV you will for the most part add an additional 1 SEER to the system!