An air-cooled refrigerated container unit using R-134a as a refrigerant has a box temperature set point of 32°F, but it is currently operating with a stable supply air temperature of 35°F. The fresh air makeup vent is closed, the unit is operating at 460 VAC/60 Hz, and the unit is in full capacity cool (modulating valve 100% open). Using the illustrated troubleshooting guide, what would be the normal range of expected discharge pressures if the ambient air temperature is 90°F? See illustration GS-RA-52.
• Compressor discharge pressure vs. ambient air temperature relationship on the chart • Difference between the 35°F box graph and the 0°F box graph • Reading the shaded band (normal operating range) at a specific ambient temperature
• Which of the two graphs on the page applies to a box temperature around 32–35°F, and why can you ignore the other one? • If you move vertically up from 90°F ambient on the bottom axis until you hit the shaded band, what pressure values (in psig) correspond to the lower and upper edges of that band? • How closely do those lower and upper values match any one of the four multiple‑choice ranges?
• Be sure you are using the upper graph labeled 35°F (1.7°C) box, not the 0°F graph • Read pressure from the right scale marked psig, not the bar scale on the left • Confirm that the entire choice range you pick falls within the shaded band at 90°F ambient
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