🔍 Key Concepts

• Function of a low-pressure cut-out switch in protecting the compressor • Where the lowest pressure in a mechanical refrigeration system is normally found during operation • Difference between suction, discharge, and liquid line pressures in a typical vapor-compression cycle

💭 Think About

• Which line (suction, discharge, or liquid) best represents the evaporator/low-side pressure that you want the switch to monitor to prevent damage? • If the refrigerant charge becomes low or the evaporator runs too cold, which line’s pressure will drop first and most directly show that unsafe low-side condition? • Would you ever want a low-pressure safety control to be seeing the high-side pressure? Why or why not?

✅ Before You Answer

• Identify which service valve is on the low side of the system and which are on the high side • Confirm which line’s pressure directly indicates evaporator (low-side) performance and protection for the compressor • Eliminate any option where the pressure being sensed would normally be high or relatively stable, instead of dropping under low-charge/low-load conditions