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January/February 2024 Tech Challenge Answer

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A logo of a yellow, red, blue, and green rubix cube with one square out of place and "Tech Challenge" written beneath it

A medium-temperature cooler utilizing R-134a with a TXV metering device with the receiver has a customer complaint of “warm.” The symptoms confirm warm product, and the condensing unit is cycling frequently on the LPC (low-pressure control). With only one problem intended, what are the “possible causes” with the following measured conditions on this field service check sheet? 

Field Service Check Sheet 

  • Compressor Discharge Temp 191 deg. F
  • Condensing Press./Temp 105 psig / 90 deg. F
  • Condensing Outlet Temp 77 deg. F
  • Condenser Sub cooling 13 deg. F
  • Condenser Split 15 deg. F
  • Entering Feed Device Temp 41 deg. F  
  • Evaporator Press./Temp 3 psig / -8 deg. F 
  • Evaporator Outlet Temp 38 deg. F 
  • Evaporator Superheat 45 deg. F
  • Compressor Inlet Temp 68 deg. F
  • Total S.H. 61 deg. F
  • Ambient Temp. 75 deg. F 
  • Room/Box Temp 52 deg. F 
  • Compressor Volts 240 V
  • Compressor Amp. Draw Low 


Answer: The problem appears to be a restricted filter/drier in the liquid line. This is verified by the entering feed device temperature of 41° F. being well below ambient temperature caused by a liquid line partial restriction causing flash off (evaporation). The low side is starved giving high superheats and the high side follows the low side because the system is not picking up much heat. The discharge temperature is high because of the high superheated inlet temperatures and low refrigerant flow.

Check out the entire January/February 2024 digital issue of ACCA Now here.

Posted In: ACCA Now, Tech Challenge

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