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the installation to run for approximately 10 to 15 minutes , measure the temperature of the air entering the coil ( on coil temperature ). Measure the temperature of the air leaving the coil ( off coil temperature ). The difference between the two is the TD .
The technician should be familiar with these TD figures , as he will check many installations to determine whether or not a job is properly adjusted for the best food-preserving conditions .
CLASSIFICATION OF PRODUCTS The temperature difference between the refrigerant in the evaporator and the fixture temperature affects the products stored . The TD of a fixture affects the humidity conditions inside the fixture . In order to secure the best results , with either forced air or gravity circulation , it is imperative that the proper TD be employed . TDs for food and materials which normally are refrigerated are available . The TDs required for forced air circulation are closer than those for gravity air circulation , but the same general rules apply to both .
SETTING OF LP SWITCH IN PRACTICE After setting an LP switch , the operation and fixture temperature must be observed for several cycles . Particular attention must be paid to the following points :
• The settings must not cause the condensing unit to short cycle .
• In an installation operating on an automatic defrosting cycle , the evaporator must be completely defrosted before the switch will cut-in .
• Avoid too great a fixture temperature difference between the cut-in and cut-out point . The fixture temperature should be maintained within ± 1.5oC of the average fixture temperature .
Remember , the range setting is equivalent to the cut-in setting and the differential set the difference between the cut-in and cutout . For this reason , the range setting , when adjusted , affects the actual setting of the cut-out point . Therefore , set the range first and then the differential .
Thanks for the question Khulani , I hope that this helps you and saves you some time .
Thanks to everybody for the overwhelming response . I receive on average over 60 questions a month and cannot publish all of them . But keep them coming , as I may answer you directly . RACA
Looking forward to hearing from you .
Grant Laidlaw
REFERENCES
1 . SETA training 2 . ACRA 3 . A Gas
Thank you for all for your interesting questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures .
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RACA Journal I October 2023 www . refrigerationandaircon . co . za