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- Evaporators freeze up
Evaporators freeze up
Danny Moore Hoshizaki America, Inc. Volume 134
Writer/Editor 618 Hwy. 74 South November 6, 1996
Peachtree City, GA 30269
Care Facsimile: (800) 843-1056
PROTECTION AGAINST VOLTAGE
The Hoshizaki KM cuber has built-in voltage protection. This serves to protect the unit against a
voltage surge or a brown-out situation. On early model KM’s using a “C” control board, high
voltage protection was accomplished by the use of a voltage protect relay. Models which have a voltage
protect relay have high voltage protection only. The relay has a 230 volt coil in parallel with the 115 volt bin
control, power circuit. It’s contacts supply power to the low voltage control transformer.
If a voltage of 150 volts or more is supplied to this 115 volt circuit,( voltage spike / surge, or a high leg supply),
the relay coil will energize and open the control transformer circuit. This will remove control voltage
from the board and shut down the unit. When the voltage returns to normal, the relay de- energizes. This
closes the relay contacts to the transformer circuit. When control voltage is restored to the board the unit
automatically restarts. All “Alpine “ control board units have high and low
voltage protection built into the board. They have a control transformer which will handle a wider supply
voltage range. As you know, a transformer has a specific ratio of input to output. When the input
changes, the output changes proportionately. The control board basically monitors the incoming
control voltage. If the control voltage falls in the established high or low range, the board does not
supply power to the other components to protect them from damage. When the supply voltage is
restored to the normal range, the correct control voltage allows the control board to automatically restart the unit.
It is important to note that this built-in voltage protection has it’s limits. If you are in a location which is known to
have severe voltage problems, additional voltage protection should be installed.
FLAKER TIMER BOARD
The solid state timer board used in Hoshizaki Flakers is a simple electronic sequence timer. In order for the
board to sequence, certain circuits must be closed. While the wiring varies slightly between models, the
basic circuits are the same. In order to diagnose a bad timer board, it is necessary
to check these circuits to assure they are operating properly. If you are trouble-shooting a timer, the first
thing you should check is the in coming control voltage. All Hoshizaki flakers have a 24 volt control transformer.
The output of this transformer is protected by a 1 amp buss type fuse. Control voltage comes in the timer on
pins 1 & 2. If you do not have 24 volts at pins 1 & 2, check the transformer and fuse.
Now check for 24 volts across pins 7 & 8. If voltage is present, the timer board has cycled up which indicates
there is not a problem in the timer board. The problem is in the gear motor relay circuit. remember that there is
a time delay from the time you turn the unit on to the time it cycles up completely. this time will be from 1 ~
2.5 minutes, depending on the model of flaker. In order for the flaker to start up, the reservoir must be
full and both float switches must be closed. This closes the control circuit to pins 3 & 4. Do not confuse these
pins with the line voltage terminals marked 3 & 4 on the compressor relay located on the board. You can check
this circuit with a volt meter across the pins or by placing a jumper across them. If the unit cycles up with
the jumper in place, the board is good and your problem is in the water relay control circuit.
Next, you should check the bin control circuit at pins 5 & 6. Check for a closed circuit with a volt meter or
place a jumper across them. If the unit cycles up with the jumper in place, the board is good and the bin
control circuit is the problem.
The last circuit check is across pins 10 & 11. These pins connect to the gear motor protect relay and will
shut down the unit if the gear motor fails. Check for a closed circuit with a volt meter or place a jumper across
them. If the unit cycles up with the jumper in place, the board is good and the gear motor protect circuit is suspect.
Now that you know that these circuits work together to allow the timer to sequence up, it should be easier to
diagnose a bad timer board.
SERVICE Q & A
Question: The evaporator section is frozen solid. Once I thaw it, what do I check?
Answer: By Duncan Sheridan You will find that the main reason for a freeze up is either a dirty evaporator
or low water flow. After de-frosting the evaporators check to see if the they are dirty i.e.: lime-scale mineral
deposits. Turn the machine on and after the compressor starts, shut off the incoming water and allow the plates
to dry. After an approximate run time of 2-4 minutes, switch the unit off and inspect the evaporator plates.
You will find that salt from a water softener can form an invisible coating on the plates. Care should be taken to
purge a water softener when charging it to eliminate this possibility. If scale or a salt coating is present, clean the
water system with Hoshizaki Scale- Away as required. Follow the instructions provided on the cleaning label on
the inside of the front cover of the machine. Verify that the incoming water flow rate is 3GPM
for KM 250-800 machines, 5GPM for KM-1200- 2400 machines. One technique to check this, is to time
the fill cycle when the sump tank is empty and see if the tank overflows in 60 ~ 90 seconds or less. If you find
the water flow is reduced, check the external water filters and replace as needed.
Inspect the water inlet solenoid valve and clean the inlet screen if necessary. Confirm that the water line size is
of adequate size, ( 3/8” o.d. for KM-250~800 models and 1/2” o.d. for KM-1200~2400 models ).
After determining the water flow is OK, check the bin control by placing ice on the bulb. The machine should
shut off in 6-10 seconds. If not, adjust it for proper operation or replace it as needed. If your machine is a
an “S” model installed on a non- Hoshizaki bin, make sure you have a bin extension
bracket installed. Hoshizaki part number 3A0408-01 is an additional stainless steel extension bracket that is to
be attached to the existing white A.B.S. plastic bulb bracket. This bracket lowers the ice level inside the bin
to where the last ice drop is able to clear the chute area into the bin, eliminating ice back-up.
Other areas to check are, is the ice still dropping into the bin when the unit cycles into the freeze mode? If
so check for cold incoming water temp or low hot gas flow. Does the inlet water solenoid valve close
completely during the freeze cycle? If not check the water valve diaphragm and clean or replace diaphragm
or valve as needed. Further testing could include checking the hot gas valve inlet and outlet temperature
during harvest making sure the valve is functioning. Also inspect the water pump to be sure it is always running
during the complete freeze cycle. Make sure the float switch is operating correctly and that it is clean. We
have a freeze-up check list available, if you need one or have any questions contact the Care Department.
KM-MODEL NUMBER NOMENCLATURE
Hoshizaki is in the process of introducing many new models. I thought this would be a good time for us to
review our model number nomenclature. The nameplates can be found on the rear left corner of the
machine and also to the left of the compressor in the compressor compartment. The following chart will help
you understand what each letter or number in our ice machine model numbers mean.
KM 1300 S A F -E
KML – Low Profile Crescent Cuber
KM – Crescent Cuber
F – Flaker
DCM – Dispenser Cubelet Maker
DB – Dispenser Bin
B – Bin
DM – Countertop Dispenser
IM – Square Cuber
Approximate production/24 Hours
@70°F Air/50°F Water
M – Modular
S – Stackable
B – Self contained with bin
N – Narrow style
A – Air cooled
W – Water-cooled
R – Remote air cooled
L – Low side
B – R-502 refrigerant unit (except KM-2400SRB3 R-22)
E – R-22 refrigerant unit (F-250BAE / IM-51BAE R-134a)
F – R-404a refrigerant unit
H – Curved front exterior panels (R-404a)
SPECIAL MODEL DESIGNATION
-E – European
-22- R-22 version of F generation
-50 – 50 Hz.
Last month we introduced the KM-1300NRF with a capacitive proximity sensor. This model is designed to
fit and operate on the larger multi-head drink dispensers. The “N” series is only manufactured in a remote
system and uses the same water circuit and refrigeration circuit as the KM-1300SRF. Other than
the 42-inch width and the new style of bin control you will not see much difference in these two units.
WATER REGULATING VALVES
In Volume 166 we discussed water-cooled machines and their operation.
We have now changed suppliers of the waterregulating valve on our water-cooled machines. The
valve we are now using is made by Johnson Controls. The major difference in the two valves is the way they
To properly adjust the valve we want to set the outlet water temp around 105°. (Reference the adjustment
chart in the Tech Specs for exact settings.) This allows us to set the head pressure without installing a gauge on
the high side of the system. Water-cooled machines have small critical charges so any loss of refrigerant,
such as when a high-side hose is removed, can have a large effect on the operation of the unit.
To determine the adjustment direction, we must first identify the valve type.
The previous valve (old style) is not painted but the top portion of the valve is gold. The new valve is gray on
the top half and has a sticker identifying it as a Johnson Control valve.With the old style valve, when you turn the adjustment
screw clockwise (CW) this will reduce the water flow, raising the head pressure and outlet water temperature.
counter-clockwise (CCW) would reduce the head pressure and outlet water temperature.
To adjust the new valve, you turn the screw CCW to reduce water flow, which will raise the head pressure
and water temperature and CW will increase water flow. This in turn reduces head pressure and water temperature.
SERVICE Q & A
Question: I have a KM ice machine that has formed large blocks of ice in the Evaporator. What is the best
way to clear the ice?
Answer by Rodd Burger: Our old friend Barney Fife, would take a great big ax or ice pick, and go POW,
POW, POW. We have even seen situations where a hammer and screwdriver were used. Obviously these
are not good methods to thaw an evaporator. Though they can be effective in removing ice, these methods
usually result in serious damage to the evaporator and loss of refrigerant.
Now that we have talked about ways not to clear a freeze up, lets look at a couple of less destructive ways
to accomplish this task. The best method will depend on what you have at your
disposal. One of the best ways is if you have access to a hot water supply. You will find a mop sink is an
excellent source for hot water. Attach a hose to the water supply and run water directly into the reservoir.
You can then put the machine in the wash position and let the pump run. It will be necessary to adjust the flow
of water coming into the sump so as not to overflow hot water into the bin. The constant flow of hot water
in the sump will insure that the sump stays full of water as well as preventing the sump water from becoming
chilled. Using this method you may be able to run another service call while the machine is being defrosted.
You can also remove the ice by just spraying hot water directly onto the frozen portions of the evaporator. This
method requires that you remain in front of the machine the entire time, but usually is a little quicker since you
can spray the water directly to the areas needed. You can also turn the machine into wash and let the
pump re-circulate water over the frozen evaporator. I would not recommend this however, if you plan to
leave the location. There are a couple of concerns. The worst problem could be that the sump tank could run
dry due to water being diverted into the bin by the ice build up. This could result in damage to the pump. You
will also find that the water will become extremely cold, reducing the effectiveness.
Be careful when using any of these methods to prevent large chunks of ice from falling on and damaging the
As you know our machine starts in the harvest cycle. I have seen technicians turning the machine on and off to
try and clear the ice. We do not recommend that the unit be continually recycled to try and clear the ice.
This method is not as effective as the others, and could cause problems with the compressor.
The most important thing, now that the ice is thawed, is to find the cause of the freeze up. You can learn more
about freeze ups in previous volumes of the Tech Tips 103 and 128. You will also find useful information
including a freeze up checklist under “Diagnosing water problems” in the Tech Specs. Following the checklist
will help you pinpoint the cause of most freeze-up problems.
Cuber Freeze Ups
Without a doubt, one of the most frequent service problems with Ice Machines is Freeze Ups.
Contrary to popular belief, there is no such creature as an unexplained or Ghost Freeze Up.
Freeze Ups are always caused by one or a combination of specific reasons.
The greatest reason by far, is a dirty evaporator. This dirt can be lime scale, calcium, iron or any
number of minerals which have collected on the evaporator over a period of time. This mineral
build-up insulates the evaporator surface and impedes heat transfer which causes ice to remain
on the plate for the next freeze cycle. This ice grows during each cycle, then forms a huge ice ball called a Freeze-Up.
Hoshizaki utilizes a hot gas defrost with water assist. The water plays a major part in helping to
transfer the heat evenly to the evaporator plate. For this reason, low water flow into the unit can
cause a Freeze-Up. Combine this with a dirty evaporator and Freeze Ups are possible.
If you have a Freeze Up, the best course of action is to clean the evaporator and check the
water flow (proper filter and line size, clean filter, and clean inlet water valve screen) first following
the procedures outlined on the inside front cover of the unit. Another frequent cause for Freeze Up is the
thermostatic bin control. If the bin control fails in the closed position, is out of position so that ice
does not touch the thermostatic bulb or, is not mounted securely or properly, ice will back up
into the evaporator and cause a Freeze Up. An inlet water valve leaking by will add water toa freeze cycle and
cause cubes to bridge downward. Also a float switch sticking closed will cause long cycles, and ice bridging. This ice
bridges in long strips and may stick to the evaporator plate to cause a Freeze Up.Lastly, a problem with the
refrigeration circuit, could be your culprit. A component failure such as a hot gas valve stuck closed, a TXV leaking
by during harvest, or a charge problem could reduce the amount of heat during harvest and
cause ice to stick on the plate. As you can see, these are several possibilities as to what causes a Freeze Up. It could be a
combination of any of the above. Nine times out of ten, simply cleaning the unit and/or correcting
the water flow will resolve your Freeze Up problem. The other items should be checked
after you have eliminated low water flow and a dirty evaporator. With the unit operating, place ice on the bin
control bulb to assure that the unit shuts down within to 10 seconds. With the unit in the freeze
cycle, check the water valve to assure that no water is leaking by. Also check to
assure that the float switch opens when the water level drops. To check the refrigeration circuit,
check the operating pressures, and watch a normal harvest to assure that all ice is removed
form the plate with 60 to 90 seconds of harvest remaining.
The information provided here should help out in pin pointing the reason for a Freeze Up.
Remember, there is definitely a valid reason for every Freeze Up. All you have to do is find it.
Controller Board History
Hoshizaki utilizes an electronic controller board as the brain of the KM series unit. Since the first
KM unit was produced in 1986, we have made 3 revisions in the controller board to increase
safeties or increase adjustment flexibility to improve water usage. The first controller board
was limited in safeties and used a variable resistor to adjust the defrost completion timer. We call
this the “A” style board. In late 1987, a revision was made to add a 60 minute freeze cycle
backup timer and the high temperature safety. The defrost completion timer adjustment was
changed to two dip switches for more consistent adjustment. This board is the “B” style board.
The “A” and “B” style boards were used on KM-451/601/631/1201 units.
The KM-452/632 and all “M” and “S” series units utilized a newer “C” style control board.
This board provided a 1 minute fill cycle, low water safety, and a 10/20 second pump out
cycle. The sequence varied slightly from the “A” or “B” board units because of the addition of the
1 minute fill cycle, In mid 1991, the Alpine board was used. This provided more flexibility in the
adjustments which results in additional water savings.
Now don’t get excited, the “A” and “C” boards are no longer available. This leaves us with two
replacement boards, the “B” and Alpine style boards. “B” boards will replace an “A” and are
used on units which have a single outlet pump motor housing and NO pump out check valve.
Remember early units did not have a pump out cycle. The Alpine board will replace a “C” style
board and is used on units with a dual outlet pump motor and a pump out check valve.
The”B” board is a drop in replacement. The Alpine board is a universal replacement for “C”
boards or original Alpine boards. A small jumper must be clipped when replacing the original
Alpine board. Instructions are included with the universal Alpine board.
Flaker Production Check
Checking the production on a Flaker is a simple process. To check the production you will need
a bucket or pan to catch the ice in and a set of scales to weigh the ice. After the unit has
operated for 10 to 20 minutes, catch the ice production for 10 full minutes. Weigh the ice to
establish the batch weight. Multiply the batch weight by 144 for the total production in 24
hours. Some prefer to catch the ice for 20 minutes and multiply the weight by 72 for a more
realistic production check. It is true that a longer catch is more accurate, however, it doubles your
test time and may only show a 1 to 2% difference in production. Performing a production check is
an excellent way to prove proper Flaker operation.
REACH-IN ALARMS / FEATURES
At the present time, Hoshizaki is producing two reach-in refrigerators. They are the RH1 (one door) and the
RH2 (two door) models. We have more models in the developmental stages including a one and two door
freezer. Several built in service features are included to provide ease of maintenance.
An electronic control board provides the control and alert functions for the reach-ins. This board is located in
the control box behind the front control panel cover. The box temperature is pre-set to provide an average
temperature of 37°F. It is adjustable through a small hole in the front cover. The adjustment range of 33
~52°F will have a differential of 6 ~7°F. The box temperature is sensed by a thermistor which is mounted
on the front wall of the evaporator compartment. A red LED display is provided to show the box
temperature and will alternately flash a code in case of a fault. The control board also provides the following
safety alert functions: 1. A High Temperature alert (E1 code) occurs if the box temperature has exceeded 18°F
above the set point for more than two hours. 2. A Low Temperature alert (E2 code) occurs if the box
temperature drops 5°F below the set point for more than one hour. These codes will automatically reset
when the temperature returns to the set point. 3. Finally, a High Pressure alert
(E4 code) occurs if the high pressure control cycles 5 times within one hour. After the high pressure problem
has been corrected, the high pressure alert must be manually reset by turning the power off and back on.
Hoshizaki reach-ins also include a cleanable condenser air filter. A clean filter light on the control panel
illuminates when the filter needs cleaning This light circuit is operated by a bi-metal thermostat located on
the compressor discharge line. If the condenser air flow is restricted, the compressor discharge temperature will
increase. At 220°F, the thermostat will operate a holding relay to turn the light on. Depressing a
momentary push button resets the light circuit after the filter has been cleaned.
The reach-ins have off-cycle defrost. Every six hours, the control board checks the evaporator temperature
through a thermistor mounted on the coil. If defrost is needed, the compressor and condenser fan stop and
allow the evaporator fan to defrost the coil. When the evaporator temperature returns to normal, the
compressor and fan restart. A backup defrost thermostat is included to provide additional defrost if
needed before the six hour check. This thermostat will stop the compressor only and will reset by evaporator
The compressor discharge line is used for condensate removal. We have improved this system to avoid any of
the normal related failures. The drain pan is made of heavy gauge stainless steel and has an overflow catch
pan for high humidity conditions. A restraining bracket and rubber bumpers eliminate tubing vibration. The discharge
line has a baked on phenolic coating to protect against corrosion.
You will also find a backup set of mullion heaters installed in the door frame which can be connected if
the first set fails. As you can see, our Engineers have taken steps to address the most common problems
related to reach-ins. That’s what Hoshizaki quality is all about.
LOCATING REMOTE CONDENSERS
Moving the ice machine heat and fan noise out of the kitchen or storage area provides a definite benefit to the
customer. Many customers prefer this remote advantage. The location of the condenser unit is
important to the proper operation of the ice machine. Lets take a look at two important aspects of locating the
remote condenser unit . The first consideration is the distance between the
condenser and unit head. The maximum distance the refrigerant lines can run is 100 equivalent feet.
Exceeding this distance puts extra load on the refrigerant system and exceeds the design specifications. You
should remember that the standard factory charge is good for up to 66 ft. Additional refrigerant must be
added for lengths between 66 to 100 ft. See the Tech Specs Pocket Guide for additional line set installation instructions.
Second, choose a site that follows the installation guidelines. The remote condenser units are designed to
be installed outside. Locate a firm flat site that is dry (doesn’t flood during the rainy season) and is well
ventilated. A “doghouse” or shed type cover is not necessary however, if one is available, it will improve
the efficiency in the hot summer sun and protect the condenser from severe snow and winter weather.
Always install the legs on the remote condenser. Raising the condenser off the rooftop allows for
considerably cooler condensing air in the summer and helps to raise it above winter snow. Wherever the condenser
is located, it must be installed in an upright position allowing for proper refrigerant flow and adequate air circulation.
SERVICE Q & A
Question: I have ice jammed in the ice drop zone and it is causing freeze-ups. What should I look for?
Answer: by Kirk Goss
There are several reasons that this may happen. The most common occurrence is when the bin control sticks
in the closed position or is out of adjustment (calibration). This condition allows ice to back up past
the bin control bulb mounting and into the ice chute, causing a freeze up condition. Check the bin control
calibration by holding ice on the control bulb. The unit should shut down within 6 to10 seconds. If not, adjust
the control to shut down properly. Another probable cause could be the physical mounting
of the bin control. On our stackable series ice machines, the bin control bulb is mounted to an eight inch long
bracket. This will put the bulb into the drop zone area in order to properly shut down the unit when the bin is
full. A loose or out of position bulb will not allow proper shut down.
On non-Hoshizaki bins, this bracket might not be long enough to reach the drop zone properly. You will need
to install a bin extension bracket part # 3A0408-01 to keep ice from backing up into the ice chute. This
bracket is included in the accessory package with each KM ”S” model machine. The extension bracket is also
necessary on any stacked application or when installing a KM-2000 or 2400.
If ice strips form on the evaporator, they can hang up at the ice cube guide just above the ice drop zone. This
will cause ice to back up in the evaporator. In this case check for plugged distributor tubes, a leaking water
valve, or a float switch stuck in the closed position. Though this is not as common, scale build-up on the ice
cube guide can cause ice to stick so that it does not slide into the bin. If the cube guide or water curtains are
out of position or broken, ice can hang up. Look for these possible situations if you notice ice jamming in the
ice drop zone.
- Hoshizaki Manuals
- Ice Maker
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Hoshizaki KM-600MAH Service Manual: Evaporator Is Frozen Up
Instruction manual – 19 pages
Specifications – 2 pages
- Table of Contents
2. Evaporator is Frozen Up
Table of Contents
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