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Refrigeration System
ANALYZING SUCTION PRESSURE DURING FREEZE CYCLE
The suction pressure gradually drops throughout the
freeze cycle. The actual suction pressure (and drop
rate) changes as the air and water temperatures
entering the ice machine change. This affects freeze
cycle times.
To analyze and identify the proper suction pressure
drop throughout the freeze cycle, compare the
published suction pressure to the published freeze
cycle time. “Operating Pressure” and “Freeze Cycle
Time” charts can be found later in this section.
NOTE: Analyze discharge pressure before
analyzing suction pressure. High or low discharge
pressure may be causing high or low suction
pressure.
Procedure
Step Example Using QR1801WM Model Ice Machine
1. Determine the ice machine operating
conditions.
Air temp. around ice machine: 80°F/26.7°C
70°F/21.1°C
Water temp. entering water fill valve:
2A. Refer to “Cycle Time” and “Operating
Published freeze cycle
Published freeze cycle
suction pressure:
Pressure” charts for ice machine model
being checked. Using operating conditions
from Step 1, determine published freeze
cycle time and published freeze cycle
suction pressure.
time:
9.6-10.6
40-20
minutes PSIG
Published Freeze Cycle Time (minutes)
2B. Compare the published freeze cycle time
and published freeze cycle suction
pressure. Develop a chart.
40 35 30 25 20
1 3 5 7 10
Published Freeze Cycle Suction Pressure (psig)
Beginning of freeze cycle:
3. Perform an actual suction pressure check
at the beginning, middle and end of the
freeze cycle. Note the times at which the
readings are taken.
59
Middle of freeze cycle:
End of freeze cycle:
PSIG at 1 minute
48 PSIG at 5 minutes
40 PSIG at 10 minutes
Time Into
Published Actual
4. Compare the actual freeze cycle suction
pressure (Step 3) to the published freeze
cycle time and pressure comparison (Step
2B). Determine if the suction pressure is
high, low or acceptable.
Result
Freeze Cycle
1 minutes
5 minutes
10 minutes
Pressure
40 PSIG
30 PSIG
20 PSIG
Pressure
High
59 PSIG
High
48 PSIG
High
40 PSIG