Diagnosing Ice Release Problems

Knowledge of the normal sequence of operation and a complete analysis of the freeze and harvest cycles in an ice machine helps diagnose release problems.

By Mitch Rens

Incorrect ice release in the harvest cycle is a common ice machine problem. Release problems can be grouped into three different categories-electrical, mechanical or refrigeration. Ice release problems can be mild or extreme-slow release or no release. The customer might complain that ice production is low, the cubes are small and/or melted or there is no ice production at all.

The following four steps aid in diagnosing ice machine release problems.

Step 1. Look in the bin. Are the cubes misshaped or in large slabs, or do the cubes appear normal? Is there still ice on the evaporator? Inspecting the ice will help determine whether the problem is electrical, mechanical or refrigeration.

Step 2. Remove any ice that is still on the evaporator, and then start a new freeze cycle. Measure the temperature of the air entering the condenser and the temperature of the water entering the sump trough. These temperatures determine the freeze-/harvest-cycle length of time. Refer to the ice machine’s manufacturer service literature to obtain the correct freeze and harvest cycle times for the ice machine being serviced.

Step 3. It is not necessary to attaché a lot of test equipment at this point. Run a test cycle and observe/answer the following:

• Verify that the sequence of operation is correct throughout the freeze and harvest cycles.
• Are the correct ice-machine electrical components energizing during the freeze cycle?
• Are all of the electrical ice machine components energizing during the harvest cycle?
• Lay your hand on the compressor several times during the freeze cycle. Does the compressor increase in temperature throughout the freeze cycle?
• Is the ice-formation pattern normal at the end of the freeze cycle?
• Is the freeze-cycle time too short or long?
• Does the control board initiate a harvest cycle?
• Does it sound like the hot-gas valve opened?
• If inspecting an air-cooled model: did the condenser fan stop during the harvest cycle? If inspecting water-cooled models: check the drain line. Does the water-regulating valve close 100%?
• Did the harvest cycle end prematurely or run the maximum specified time?
• Did all, some or none of the ice release from the evaporator? And
• If some of all of the ice released: are the back of the cubes melted or well formed? If none of the ice released: continue to the next step.

Step 4. After observing a complete freeze and harvest cycle, determine if the failure falls into an electrical, mechanical, refrigeration or harvest cycle category. Descriptions of each of the four main categories follow:

Electrical problems

This is easy to diagnose when you know the sequence of operation. If one of the components did not energize during the freeze cycle, more investigation is required.

• If line voltage was present at the component but it did not energize, the diagnosis is complete;
• If the ice machine never initiates a harvest cycle, check the sensor, ice thickness probe, pressure control, thermistor or timer. If the sensor is clean, correctly adjusted and functional, check the control board;
• If the hot-gas valve has line voltage but never opened, check the solenoid coil for continuity. If the coil is not at fault, the solenoid valve will require replacement; and
• If the harvest cycle ends early, check the sensor that signals the control hoard to stop the harvest cycle and start another freeze cycle.

After verifying that the electrical system is working correctly, the problem is either mechanical or refrigeration. The information needed to determine this was gathered after testing the one freeze and harvest cycle. At the end of the harvest cycle, place the toggle switch in the off position and then remove and inspect the ice slab. Do not use a screwdriver. If the cubes are deformed and melted away, it is a mechanical problem. If the cubes are well-defined and show minimal signs of melting, it is a refrigeration problem.

Mechanical problems

The number-one cause of mechanical problems is a dirty evaporator, but be sure to dry the evaporator before inspecting it. A good analogy for a dirty evaporator is a car being driven in the rain; the car looks nice and clean when the rain is falling on it, but once dry, dirt appears over the entire car. Ice machine evaporators react the same way; they look clean when they are wet, hut once dried, the dirt becomes very obvious.

Dirty evaporators account for more release problems than all other problems combined. A common observation found when an evaporator is dirty is the bottom of the ice sheet sags forward half way through the harvest cycle. Near the end of the harvest cycle the top of the ice sheet starts to release, the bottom settles back into the evaporator and the control board ends the harvest cycle. The sheet of ice may drop at this time or when water starts to flow over the evaporator. The ice will release very erratically with this scenario and can erroneously give the impression that all that is necessary to fix the problem is to adjust the harvest cycle to make it longer.

The fallacy of this line of reasoning would he demonstrated if the harvested ice was weighed and the actual production of the ice machine was calculated. Clean the evaporator before proceeding. This does not mean putting the toggle switch in wash and adding a little cleaner. Disassemble the ice machine and clean every component with cleaner and a suitable brush. All foreign material must he removed from the evaporator. Inspect the evaporator for physical damage that may have been caused by a screwdriver, ice pick, hammer or improper cleaners. Inspect the seal around the evaporator plate and the extrusions. Extrusions go around the evaporator like a picture frame. Is the seal intact, are the extrusions cracked? Plastic does not conduct heat as well as metal. Since the freeze cycle is longer than the harvest cycle, ice can build up on or behind the plastic. The harvest cycle is too short to melt ice in these locations and the ice hangs up. Watch the ice sheet closely during the harvest cycle and possibly witness this ice act like a hinge.

If the evaporator is damaged and needs to be replaced, consider the following carefully:

• Age and general condition of the ice machine;
• Cost of a replacement evaporator and labor to install it;
• Type, cost and availability of the refrigerant; and
• The probability of the ice machine losing another component in the next six months. This is the classic "this has not worked right since the last time you were here complaint." It is best to give customers all of the options and explain the possible consequences and costs of their decision.

Refrigeration problems

After electrical and mechanical problems have been eliminated, start looking for refrigeration problems. The freeze-cycle time must he correct before diagnosing the harvest cycle. If the freeze cycle is too short or too long, correcting it will most likely correct the release problem. To do this, contractors need their tools.

Attach your manifold gauge set and a thermometer thermocouple on the compressor discharge line within 6 in. of the compressor.

Check the service manual and determine the correct suction and discharge pressures.

The freeze cycle discharge pressure must he normal. The discharge pressure is normal when the actual pressure falls within the published pressure range for the ice machine's operating conditions. High- or low discharge pressure will affect the suction pressure. Always correct discharge- pressure problems before suction pressure problems. Ice release and low-discharge pressure problems go hand-in-hand.

Low-discharge pressure in the freeze cycle will result in faster-than normal freeze cycle times. Possible causes include incorrect water flow, water-regulating valve set too low, Fan-cycling control failed closed or head-pressure control valve is not bypassing the condenser. Note that the head-pressure control valve will not be the problem when ambient temperatures are above 75°F

The freeze-cycle suction pressure must be normal. 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 the freeze-cycle times. To analyze and identify the correct suction-pressure drop, compare the published suction pressure to the published freeze-cycle time.

The compressor must be warm in the freeze cycle. The compressor develops heat throughout the freeze cycle. This heat supports the harvest cycle pressures. Lack of heat in the freeze cycle results in a harvest problem. Knowing if the discharge line temperature is increasing, decreasing or remaining constant is an important diagnostic tool. Compressor discharge line temperature on a correctly operating ice machine steadily increases throughout the freeze cycle.

Higher ambient-air temperatures at the condenser equal higher discharge-line temperatures at the compressor. Lower ambient-air temperatures at the condenser equal lower-discharge.

Ambient air temperature also affects the maximum discharge line temperature. Higher ambient-air temperatures at the condenser equal higher discharge-line temperatures at the compressor. Lower ambient-air temperatures at the condenser equal lower-discharge line temperatures at the compressor. If the compressor is cold and the discharge line is cool below 150°F at the end of the freeze cycle--check for a flooding expansion valve. Check bulb insulation and bulb mounting before replacing the valve.

• The freeze cycle time must be within specification at the air/water temperature; and
• Verify that the ice formation pattern is correct and evenly covers the entire evaporator surface at the end of the freeze cycle.

Harvest cycle problems

This is a short list:

• In air-cooled ice machines: the condenser fan will not stop in the harvest cycle. This shows up rapidly at low ambient temperatures-the harvest pressures fall throughout the harvest cycle.
• In water-cooled ice machines: check the drain line. The water-regulating valve must close 100% in the harvest cycle. If the valve weeps through the harvest, pressures will fall throughout the harvest cycle.
• Although electrically energized, the hot gas valve is not fully open: and
• If the ice machine is a remote model, it may have a harvest pressure-regulating system.

During the freeze cycle, the expansion valve throttles down as the load decreases. When the harvest cycle starts, the check valves-used to prevent refrigerant migration in the off cycle-prevent refrigerant from entering the evaporator from the condenser. The ice machine is now undercharged for the harvest cycle. The harvest pressure-regulating solenoid is energized with the hot-gas solenoid valve. The harvest pressure regulating valve will add refrigerant from the receiver until the suction pressure in the evaporator reaches 75psi. The ice machine now has enough refrigerant for the harvest cycle.

Ice release problems can be very easy to diagnose or require time and patience. If after following these steps, the cause of the problem still cannot be determined, the problem typically involves something that was overlooked on the evaporator. Again, dry the evaporator, inspect it closely and clean it again.

Mitch Rens is service publications manager of the Manitowoc Foodservice Group. For more information, call 920-683-7725 or e-mail mitchell.rens@manitowoc.com.