March/April 2024 Tech Challenge Answer

---

A reach-in cooler utilizing R-134a with a capillary tube feed device has a customer complaint of warm product. The symptoms at the convenience store confirm inadequate cooling and the compressor appears to be short cycling on the high- or low-pressure control. What are the “possible causes” (Note: There is only one problem intended) with the following measured/calculated conditions on this field service check sheet? 

Field Service Check Sheet 

• Compressor Discharge Temp. 205 deg. F. 
• Condensing Press./Temp. 108 psig / 92 deg. F. 
• Condensing Outlet Temp. 76 deg. F. 
• Condenser Sub cooling 16 deg. F. 
• Condenser Split 17deg. F. 
• Entering Feed Device Temp. 44 deg. F. 
• Evaporator Press./Temp. 5 psig / -3 deg. F. 
• Evaporator Outlet Temp. 37 deg. F. 
• Evaporator Superheat 40 deg. F. 
• Compressor Inlet Temp. 68 deg. F. 
• Total S. H. 71 Deg. F. 
• Ambient Temp. 75 deg. F. 
• Room/Box Temp. 51 deg. F. 
• Compressor Volts 240 V. 
• Compressor Amp. Draw Low 

Answer: The probable cause of the warm beer is likely to be a liquid line restriction. The temperature of the liquid entering the capillary tube is well below the ambient temperature, telling us that evaporation has taken place before the feed device. If the liquid line and filter/drier are also cold, a partially restricted filter is probably the culprit. The pressures and amp draw are low, and it is cycling on the low-pressure control because the liquid line is a very small evaporator, and it is not picking up very much heat. The system is not working very hard and what work it is doing is in the wrong place.

Check out the latest digital issue of ACCA Now here.

---

Posted In: ACCA Now, Tech Challenge