Service manual

Section 7 Refrigeration System
7-19
ANALYZING DISCHARGE PRESSURE
DURING FREEZE OR HARVEST CYCLE
Procedure
1. Determine the ice machine operating conditions:
Air temp. entering condenser ______
Air temp. around ice machine ______
Water temp. entering float valve ______
2. Refer to Operating Pressure Chart for ice machine
being checked. (These charts begin on page 7-31.)
Use the operating conditions determined in Step 1
to find the published normal discharge pressures.
Freeze Cycle ______ Harvest Cycle ______
3. Perform an actual discharge pressure check.
Freeze Cycle
PSIG
Harvest Cycle
PSIG
Beginning of Cycle __________ __________
Middle of Cycle __________ __________
End of Cycle __________ __________
4. Compare the actual discharge pressure (Step 3)
with the published discharge pressure (Step 2).
The discharge pressure is normal when the actual
pressure falls within the published pressure range
for the ice machine’s operating conditions.
Freeze Cycle Discharge Pressure High Checklist
Possible Cause Check/Correct
Improper installation • See “Installation/Visual Inspection Checklist” on page 7-10
Restricted condenser
air flow (air-cooled models)
• High inlet air temperature (110°F/43.3°C max.)
• Condenser discharge air recirculation
• Dirty condenser filter
• Dirty condenser fins
• Defective fan cycling control
• Defective fan motor
Restricted condenser water
flow (water-cooled models)
• Low water pressure (20 psi min.)
• High inlet water temperature (90°F/32.2°C max.)
• Dirty condenser
• Dirty/defective water regulating valve
• Water regulating valve out of adjustment
Improper refrigerant charge • Overcharged
• Non-condensibles in system
• Wrong type of refrigerant
Other • Non-Manitowoc components in system
• High side refrigerant lines/component restricted (before mid-condenser)
• Defective head pressure control valve (remote models)
Freeze Cycle Discharge Pressure Low Checklist
Possible Cause Check/Correct
Improper installation • See “Installation/Visual Inspection Checklist” on page 7-10
Improper refrigerant charge • Undercharged
• Wrong type of refrigerant
Water regulating valve
(water-cooled condensers)
• Out of adjustment
• Defective
Other • Non-Manitowoc components in system
• Defective head pressure control valve (remote models)
• Defective fan cycle control
NOTE: Do not limit your diagnosis to only the items listed in the checklists.