When investigating problems with an open display case, a technician must not only look at the mechanical refrigeration circuit but also at the air curtain as the possible source of the problem. When an air curtain becomes disturbed, warm store air can enter the case, causing the temperature of the case and its product to rise.
Many factors can disrupt an air curtain. As a technician, you need to identify the source and correct the problem. Always measure the discharge air velocity of the air curtain and look for sources of the disturbance. By doing this, you should be able to discover most problems associated with these air curtains.