Articles by John Tomczyk

The Professor: Restricted TXV Metering Device

January 17, 2011
This article explores how a restricted metering device will affect system performance and efficiency. The system is a commercial refrigeration system with a TXV as the metering device. The refrigerant being used is HFC-134a. Very similar results will occur if an automatic expansion valve (AXV) is used.
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The Professor: Symptom Variations With Different Devices

December 6, 2010
Symptoms for a refrigeration system with an overcharge of refrigerant are (a) high discharge temperatures, (b) high condenser subcooling, (c) high condensing pressure, (d) higher condenser splits, and (d) slightly higher evaporator pressures. However, these are for a system with a conventional TXV. What if the system has an automatic expansion valve or a capillary tube?
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The Professor: Advanced Leak Detection

November 1, 2010
My Oct. 4 column discussed leak detection and provided details on basic detection methods. This column looks at more advanced methods. The Oct. 4 column outlined various classes of leaks with standing leaks as the most common. This article begins with a discussion of how to test for pressure-dependent leaks.
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The Professor: Basic Leak Detection Methods

October 4, 2010
Every environmentally conscious service technician should spend time learning how to check for refrigerant leaks in refrigeration and/or air conditioning systems. Ozone depletion, global warming, and the increasing price of refrigerants are forcing technicians to become better and more thorough leak detectors.
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The Professor: Checking on Refrigerant Overcharge

September 6, 2010
This column discusses refrigerant overcharge. The check sheet shown depicts a refrigeration system with an overcharge of refrigerant. The system is a low-temperature HFC-134a unit with a TXV/receiver.
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The Professor: Flooding and Slugging

August 2, 2010
HVACR field service terminology is often confusing and misused even by the most seasoned service veterans. Two important service terms that are often misunderstood and misused are ‘flooding’ and ‘slugging.’ Each one will be thoroughly defined and explained as they apply to refrigeration and air conditioning compressors.
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The Professor: Systematically Troubleshoot an Evaporator

July 5, 2010
Systematic troubleshooting using a system check sheet is still the best method for the conscientious service technician to pinpoint hard-to-find system problems. Here we will explore how evaporators can become oil logged, and include symptoms with explanations for a system with an oil-logged evaporator.
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The Professor: Refrigerant Migration

June 7, 2010
Refrigerant migration is defined as refrigerant, either liquid or vapor, traveling to the compressor’s suction line or crankcase during the off cycle. During the off cycle, or especially during a long shutdown, refrigerant will want to travel, or migrate, to a place where the pressure is the lowest.
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The Professor: Frost on the Compressor's Head

May 3, 2010
Many service technicians believe that if there is frost on the compressor’s head, there is cause for alarm. This is simply not true. Frost is simply frozen dew. Consider a low temperature commercial refrigeration application operating with 7° of evaporator superheat and 40° of compressor superheat.
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The Professor: Compressor Overheating

April 5, 2010
My column in the March 8 issue of The NEWS dealt mainly with reciprocating compressors experiencing low head pressure and high suction pressure from bad valves. This column takes an in-depth look at high compression ratios that cause compressor overheating along with high compressor discharge temperatures.
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