Analyzing Suction Pressure During Freeze Cycle - Manitowoc S600M Service Manual

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.
Procedure
Step
1. Determine the ice machine operating
conditions.
2A. Refer to "Cycle Time" and "Operating
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.
2B. Compare the published freeze cycle time
and published freeze cycle suction pressure.
Develop a chart.
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.
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.
7-12
NOTE: Analyze discharge pressure before analyzing
suction pressure. High or low discharge pressure may
be causing high or low suction pressure.
Example Using SY605W Model Ice Machine
Air temp. entering condenser:
Air temp. around ice machine:
Water temp. entering water fill valve:
Published freeze cycle time:
8.5 - 9.8 minutes
Published Freeze Cycle Time (minutes)
1
58
Published Freeze Cycle Suction Pressure (psig)
Beginning of freeze cycle:
Middle of freeze cycle:
End of freeze cycle:
Time Into Published
Freeze Cycle Pressure
1 minutes 58 PSIG
5 minutes 43 PSIG
10 minutes 28 PSIG
Published freeze cycle suction pressure:
58-28 PSIG
5
3 8 10
43
52 33 28
70 PSIG at 1 minute
57 PSIG at 7 minutes
40 PSIG at 14 minutes
Actual
Pressure
70 PSIG
48 PSIG
40 PSIG
Part Number 80-1630-3
Section 7
90°F/32.2°C
80°F/26.7°C
70°F/21.1°C
Result
High
High
High