Manitowoc STH042 4/16, Technician'S Handbook

Page: 81 / 146

Part Number STH042 4/16 81
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