ICE MACHINES Q-Model Service Manual

Refrigeration System Section 7ANALYZING SUCTION PRESSUREDURING FREEZE CYCLEThe suction pressure gradually drops throughout thefreeze cycle. The actual suction pressure (and drop rate)changes as the air and water temperatures entering theice machine change. This affects freeze cycle times.NOTE: Analyze discharge pressure before analyzingsuction pressure. High or low discharge pressure maybe causing high or low suction pressure.To analyze and identify the proper suction pressure dropthroughout the freeze cycle, compare the publishedsuction pressure to the published freeze cycle time.“Operating Pressure” and “Freeze Cycle Time” chartscan be found later in this section.ProcedureStep1. Determine the ice machine operatingconditions.2A. Refer to “Cycle Time” and “OperatingPressure” charts for ice machine model beingchecked. Using operating conditions from Step1, determine published freeze cycle time andpublished freeze cycle suction pressure.Example Using QY0454A Model Ice MachineAir temp. entering condenser:90°F/32.2°CAir temp. around ice machine:80°F/26.7°CWater temp. entering water fill valve:70°F/21.1°CPublished freeze cycle time: Published freeze cycle suction pressure:13.7 - 14.1 minutes 55-36 PSIGPublished Freeze Cycle Time (minutes)1 3 5 7 9 12 142B. Compare the published freeze cycle timeand published freeze cycle suction pressure.Develop a chart.3. Perform an actual suction pressure check atthe beginning, middle and end of the freezecycle. Note the times at which the readings aretaken.4. Compare the actual freeze cycle suctionpressure (Step 3) to the published freeze cycletime and pressure comparison (Step 2B).Determine if the suction pressure is high, lowor acceptable.55 52 48 44 41 38 36Published Freeze Cycle Suction Pressure (psig)Beginning of freeze cycle:Middle of freeze cycle:End of freeze cycle:Time IntoFreeze Cycle1 minutes7 minutes14 minutesPublishedPressure55 PSIG44 PSIG36 PSIG59 PSIG at 1 minute48 PSIG at 7 minutes40 PSIG at 14 minutesActualPressure59 PSIG48 PSIG40 PSIGResultHighHighHigh7-18 Part No. 80-1100-3