Manitowoc MD0420A, Technician'S Handbook

Page: 70 / 132

70 Part Number 040005626 5/17
Procedure
Step
1. Determine the ice machine operating conditions.
Example:
Air temp. entering condenser: 90°F/32.2°C
Air temp. around ice machine: 80°F/26.7°C
Water temp. entering water fill valve: 70°F/21.1°C
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.
Example:
Published freeze cycle time: 14.8 - 15.9 minutes
Published freeze cycle suction pressure: 65 - 26 psig
2B. Compare the published freeze cycle time and
published freeze cycle suction pressure. Develop a chart.
Example:
Published Freeze Cycle Time (minutes)
1 2 4 7 10 12 14
| | | | | | |
65 55 47 39 34 30 26
Published Freeze Cycle Suction Pressure (psig)
In the example, the proper suction pressure should be
approximately 39 psig at 7 minutes; 30 psig at 12
minutes; etc.
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.
Example:
Manifold gauges were connected to the example ice
machine and suction pressure readings taken as
follows: ________ PSIG
Beginning of Freeze cycle: 79 (at 1 min.)
Middle of freeze cycle: 48 (at 7 min.)
End of freeze cycle: 40 (at 14 min.)
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.
Example:
In this example, the suction pressure is considered high
throughout the freeze cycle. It should have been:
Approximately 65 psig (at 1 minute) – not 79
Approximately 39 psig (at 7 minutes) – not 48
Approximately 26 psig (at 14 minutes) – not 40