HIGH SUPERHEAT (Evaporator Outlet)
HIGH SUPERHEAT (Evaporator Outlet)
1.1 Flash Gas in the Liquid LineFlash gas at the inlet of a Thermal Expansion Valve (TEV) will obstruct the flow of liquid refrigerant and therefore, starve the evaporator. There is nothing good about the presence of “Flash Gas” and if it does occur, then the following conditions can be expected:a) The valve will operate inefficiently.b) The system loses some of its capacity.c) Superheat increases.Probable Cause• Insufficient Refrigeration Charge• Excessive pressure-drop in the liquid line or excessive vertical lift in liquid line pipe-work.NOTE: If there is no sight glass in the liquid line at the TEV inlet:a) Flash gas can sometimes be heard by a characteristic ‘whistling’ sound at the TEV.b) Flash gas can also be detected by installing a schrader valve at the TEV inlet. Take a pressure and temperature reading at this point. If the temperature is above it’s saturation temperature (using a pressure-temperature chart) then flash gas is present.• Lack of positive head pressure control will cause erratic head pressures.Remedy• Add refrigerant to the system, which will raise the head pressure. There are several methods to follow for charging a system correctly: superheat method, subcooling method, current draw, temperature difference across components, etcReview or install sufficient head pressure control.
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