Fixed orifice superheat will vary with mass flow rate and interior heat load. For example, let's say you have a hot day at 102 degrees, and an interior that the system is able to maintain comfortably at 74 degrees. Since the outdoor ambient is high, the condenser will be running a higher head pressure. This places more pressure on the liquid column feeding the fixed orifice, resulting in a greater pressure differential across the orifice and into the evaporator.
Originally posted by pipe threader
Under for your interest, the topic, Troubleshooting The
Refrigerent System With Superheat & Subcooling.
It ststes under critical temperture differences.
The low side superheat should be between 20 and 30 de-
grees. A/C manuals i have looked at show adjusting super
heat on fixed orfice systems down to 5 degrees. What am
i missing here?