A dual evaporator fed by capillarys should never let one evaporator run unloaded. Due to risk of flooding in the second evaporator as the transition from unloaded to load will increase the massflow; the refrigerant will head preferably to the zone of lower restriction, which will be the unloaded evaporator; effectively starving the loaded evaporator.
This is why a superheat valve is often used in any multiple capillary system of decent size. Sadly these valves are very expensive, and too large for our systems. Or more commonly TXV's fed by a common receiver but then "hidden" from each other with a valve that sets the suction pressure so that the TXV's do not begin "seeking" constantly. Many TXV's have an external connection that is meant to help detect the suction pressure across evaporators with large pressure drops. These can actually be helpful in fighting "searching" by connecting the valves as normal, and then linking these connections further with a piece of capillary tubing of similar pressure drop to the evaporators selected.
Unless that unit has a fairly extensive suction line heat exchanger (not just capillary wrapped to the flex/suction), running one evaporator unloaded would be a bad idea. It might work fine for a time, but it will certainly hurt the load capacity and risk floodback.
Edited by NoL - 5/21/12 at 12:36pm
