Manual defrost units are the least expensive and should be defrosted every four weeks in the summer, and every eight to ten weeks in the winter. Usually, the refrigerator is shut off and permitted to stay off overnight to become completely defrosted. (Or for faster results, a pan of hot water is placed in the freezer while the unit is turned off for a few hours). The freezer temperature ranges between 5°F and 15°F, and the temperature in the fresh-food compartment ranges between 38°F to 45°F. Normal low-side pressure in manual defrost units varies between 10-15 psi. Cycle-defrost refrigerators are less troublesome than the manually defrosted units, but they are not as sophisticated as the fully automatic units. In the cycle-defrost type, defrosting occurs each time the thermostat becomes satisfied. An electric heating element attached to the extension of the evaporator in the fresh-food compartment (fresh-food evaporator) becomes energized to ensure thorough de-icing of the fresh-food evaporator in the off cycle (see fig. 5).
Cycle-defrost refrigerators should be manually defrosted two to four times a year. In cycle-defrost units, the temperature ranges between 0°F and 10°F in the freezer compartment, and 38°F to 45°F in the fresh-food compartment. The normal low-side pressure ranges between five and ten pounds per square inch (5-10 psi).