Short freeze cycles and/or makes small cubes
HOSHIZAKI TECHNICAL SUPPORT
Danny Moore Hoshizaki America, Inc. Volume 140
Writer/Editor 618 Hwy. 74 South June 16, 1997
Peachtree City, GA 30269
HTS Facsimile: (800) 843-1056
DIAGNOSING HEAD PRESSURE PROBLEMS
Head pressure problems in a refrigeration system fall into two different categories. There are definite
symptoms for low head pressure and high head pressure problems.
First let’s take a look at low head pressure problems. Low head pressure can cause poor harvest, low suction
pressure, and little or no ice production. These symptoms will definitely occur if the refrigerant charge is
low. A low charge is normally the result of a system leak or an improperly charged unit. The refrigerant
charge is critical for proper operation. Always weigh-in the charge per the amount listed on the unit nameplate.
All leaks must be repaired using proper refrigeration practices.
Generally, anything that causes low suction pressure will cause low head pressure and vise versa. On a water
cooled unit, a water regulating valve that is adjusted or stuck wide open can drop the head pressure below
normal. Low head pressure can also be caused by a restriction in the liquid flow to the evaporator. This
could be caused by a restricted drier or the liquid line valve or TXV not opening properly. Also, if the hot gas
valve does not open during harvest, any unit with a liquid line valve will pull into a vacuum and cause low
head pressure as well as an extended harvest period. Extremely low ambient conditions or a head pressure
control (headmaster) that is stuck so that it does not bypass will reduce the head pressure. This will also
occur if the headmaster is set too low. The last item on this list is an inefficient compressor. As valves get weak,
the compression ratio will be reduced so that the head pressure will run below normal.
All Hoshizaki ice machines have an internal auto-reset high pressure switch. This switch is a safety to protect
against excessive high pressures. The head pressures in an ice machine will vary somewhat with changing
ambient conditions. You will find however, that the average head pressure of a R-22 unit will run from 220
to 230 psig. If the unit cycles off on the high pressure switch, a problem exists.
The number one reason for high head pressure is reduced heat transfer in the condenser. On a water
cooled model check for internal scale build up or reduced water flow through the condenser, i.e.
restricted water regulating valve, etc. On air cooled models it could be inadequate clearances, extreme
ambient temperatures, plugged air filters or dirty or loose condenser fins. An inoperative fan motor or a unit
without adequate clearance for proper air flow will also cause elevated head pressures. You should always
eliminate low heat transfer items first. On remote systems, check the headmaster. If this valve
sticks in the bypass mode, head pressure will increase. On self contained models check for a hot gas valve/coil
problem. If the coil overheats and the valve closes before the harvest is compete, the unit usually shuts
down on the high pressure safety. Also check for a
TXV that is fully open as the harvest ends. This can cause a head pressure spike and shut down the unit on
the high pressure safety. Usually, it is caused by a loose bulb or a sticking TXV valve.
Finally check for an overcharge of refrigerant or noncondensibles in the system. A thorough cleanup is
required if non-condensibles are present. As always, Hoshizaki recommends using proper refrigeration
practices including drier replacement when servicing a sealed refrigeration system.
SMALL KM CUBES
Small cubes on a KM cuber mean only one thing. There’s not enough water to make normal size cubes or
the water is disappearing. During harvest, the reservoir should fill to overflowing. If it does, there is plenty of
water in the reservoir for a full batch of normal size KM cubes. If it doesn’t fill to overflowing check the
incoming water supply. A plugged external filter or inlet water valve screen is likely. Low water pressure or an
improper inlet water line size is also a possibility. If the reservoir filled properly during harvest, the water
had to go somewhere. In this case check for leak by at the pump-out check valve caused by dirt, scale, or a
weak spring. Also look for a missing displacement cap or o-ring for the drain stand pipe. A water trail caused
by shipping tape, an out of position ice chute guide, or algae can cause water to run into the bin. There is also
the remote possibility of a leaking reservoir. Search until you find the missing water culprit and correct it, and
the KM cube size should return to normal.
SERVICE Q & A
Question: The toggle switch is “OFF” but the compressor is still running. What do I check?
Answer: by Rodd Burger Many times we hear this complaint on the technical support line. For the most
part this problem is easy to resolve. This is however, a serious problem and can cause severe damage to the
compressor if not corrected.
The most common reason for this call is the control board has been changed and was incorrectly installed.
When replacing a board in units that were originally manufactured with a Alpine board a modification must
be made. The modification is to cut the black jumper located between X3 and X4 relays. Cutting this jumper
allows the universal replacement part number 2U0139- 01 to fit the original Alpine application.
The easiest way to determine if the wire should be cut or not is to look at the K1 connector. If a white wire is
not included in this connector wiring, the jumper should be cut. When the wire is not cut the magnetic contactor
will remain energized when the control switch is in the off position.
Another reason for this symptom is a sticking magnetic contactor. There are two ways to check for
this problem. First check for voltage at the coil of the contactor. The coil terminals are usually marked with A
and B. Use your voltmeter to check for 120 volts across these points. If no voltage is present and the
compressor is running, the contactor points may be welded together or stuck closed. Another way to
confirm a stuck contactor is to pull one wire off of the contactor coil at A or B, if the compressor does not
stop running, check for a stuck contactor. Many times you can take the butt of a screwdriver and rap the side
of the contactor to dislodge the stuck contacts and stop the compressor. Always replace the contactor in this case.
If the compressor stops when one wire is removed from the coil or you find 120 volts applied to the coil, you
may need to look at the next scenario. Finally, the compressor may run with the toggle switch
in the off position if the magnetic contactor is energized by back feed voltage. This may happen if a nondedicated
neutral wire is installed on the unit. 208/230 volt 1Æ models use 115 volt controls. It is very
important that these units be supplied with a dedicated neutral. This is a neutral conductor that runs directly
from the power supply neutral lug to the ice maker. A dedicated neutral should not be connected on 3Æ models.
In some cases, if the neutral is connected with other neutral wires from an outside source (non-dedicated) a
back feed voltage or back EMF may occur. This back feed voltage can be caused by a component failure or
through an inductive load in another circuit. To check for this problem, check voltage at the coil of the
contactor while the unit switch is in the off position. If voltage is present, check from neutral to ground. If you
have voltage to ground, back feed voltage is occurring and you should investigate the external wiring and connections.
We hope these suggestions will help the next time you experience this mysterious symptom.
Danny Moore Hoshizaki America, Inc. Volume 143
Writer/Editor 618 Hwy. 74 South September , 1997
Peachtree City, GA 30269
Ph: (800) 233-1940 Fax: (800) 843-1056 E-mail: [email protected]
The size of the incoming water supply line is an important factor in proper ice machine operation. Many
manufacturers use a float valve assembly to fill their reservoir. Generally, they require only a ¼”OD inlet
line. A ¼”OD tube has a 1/8” internal diameter which has a .049 in² internal area. This ¼” tubing will allow
about a ½ gallon per minute service flow rate. A float valve assembly slowly fills the reservoir as needed. This
allows make up water to enter the reservoir during the freeze cycle. In the summer, warm inlet water tempers
the reservoir water and extends the freeze cycle time reducing efficiency.
Hoshizaki uses an inlet water valve solenoid to bring in make up water during the harvest cycle only. This batch
method provides better efficiency. The KM sequence fills the reservoir with enough water to make a full batch
of ice then leaves the inlet water valve off during the freeze cycle. This allows the unit to cool the water and
make a batch of ice without being affected by additional water entering the reservoir.
Proper water line size is important for both ice making and to assist the harvest. Hoshizaki KM cuber models
up to KM-800 require a 3/8” OD inlet water line. KM-1200 and larger units require a ½” OD inlet water
line. You can use ½” tubing on all models as a standard. This will allow you to stock one size tubing and fittings
for any installation. A 3/8” tubing has a ¼” internal diameter which has an area of .196 in². Almost four
times the internal area of ¼” tubing. A ½” OD tube has a 3/8” internal diameter and a total area of .442 in².
The correct size tubing is necessary to provide adequate flow rate to the reservoir. It is important
to remember that a ¼” water line will not provide the flow rate necessary to fill a KM reservoir and assist in
harvesting the ice. If the water line is undersized or the flow rate is restricted, you can expect poor harvest and
possible low production.
Before installing a KM unit always check the water supply line size. Check the supply all the way back to
the source. Look for restrictions caused by improper connections. For example, a cut off valve that is smaller
than the supply will cause a restricted flow rate. Restrictions can also occur if the filter manifold and
connections are smaller than the supply line. If you are stacking two “S” models, make sure that the main
supply line is large enough to supply adequate water flow for both units at the same time. If two ½”supplies
are needed, a ¾”main is required. This is standard plumbing practice.
Always check the installation manual or your Tech- Specs pocket guide for the proper water line size. You
will find that following Hoshizaki specifications and using standard piping practices will eliminate many water
The purpose of this article is to let you know about the videos produced by the Technical Support Department.
We now have a total of six service training videos available at a nominal charge through your local
Hoshizaki distributor. Three new videos were just completed in mid August.
Videos are an excellent training tool because you have the ability to stop and back up to review a subject as
many times as necessary. The old adage “a picture is worth a thousand words”is true.
The KM Cuber video #80017 and the Flaker & DCM video #80018 were made available in December 1995.
These videos cover the service features, a thorough operational sequence and the cleaning and preventative
maintenance procedures for their respective models. A good understanding of the sequence of operation is the
most important tool you can carry to a service call. These tapes provide you with that tool.
The Preventative Maintenance video #80031 includes KM, Flaker, & DCM products. You will find the
cleaning and PM sections from #80017 & 80018 which provide details on the PM steps including auger
bearing inspections. This is a good tape to supply for the customer who likes to do their own minor maintenance.
The new videos include Hoshizaki Ice Machine Installation #80035. Technicians are walked through an
installation of two stacked KM-1200SRE units. General specifications as well as the important aspects
of a proper installation for all models are highlighted. It would benefit every technician to see this video.
KM Cuber Diagnosis video #80033 and Flaker diagnosis #80034 covers the procedures for diagnosing
the control circuits for each model. A detailed explanation of how to use the ten minute check out
procedure to find a problem on the KM and steps for checking the Flaker timer board are covered. Both
symptoms and check out procedures for the control components are included. It is a good idea to review
the basic sequence videos prior to viewing these diagnosis videos.
SERVICE Q & A
Question: I am servicing a KM cuber that has consistent 5 minute freeze cycles. What can cause this short cycling?
Answer: by Rodd Burger
This is one of the most common questions asked to the Technical Advisors. Before we look at the possible
causes we must understand two things. The first is that the KM series goes into harvest by water level, and not
by temperature. This occurs as the water level drops and the float switch opens.
The second is that the water level is controlled by the stand pipe in the reservoir and not by the float switch or
control board. The reservoir of the KM series cuber fills with water one time during the ice making cycle.
This occurs during the initial fill and harvest cycle only. The reservoir should fill and begin to over flow the stand
pipe within about 90 seconds if proper water flow is available.
Now, we will look at the possible causes for a 5 minute freeze time. The first items to check are the float switch
and control board operation. This is done by placing a jumper across the float switch connector and allowing
the unit to sequence into the freeze cycle. If the unit continues to sequence into the harvest cycle after 5
minutes, replace the board. If the unit remains in the freeze cycle, check the
operation of the float and the following items. It is possible that the reservoir was not completely full at the
beginning of the freeze cycle. This can be easily checked by watching the unit drain during the harvest cycle.
Water should overflow the stand pipe and drain within the first 60 to 90 seconds of a normal harvest cycle.
If water does not overflow the drain, check for proper water line size and pressure. Also check for a plugged
external filter system or inlet water valve screen, and check for proper operation of the water valve. If the
reservoir fills properly, the next possibility is that the pump out check valve is stuck open. The easiest way
to check for this problem is to see if you have water coming from the drain during the freeze cycle. This tells
you that the check valve is stuck open, dirty, or has a weak spring. Disassemble the check valve housing and
clean the valve seat. If the spring is weak, a temporary fix is to stretch it a little. This will get you by until you
can replace it with a new one. Checking these items should help you resolve a contsistent 5 minute freeze cycle.
Danny Moore Hoshizaki America, Inc. Volume 127
Writer/Editor 618 Hwy. 74 South April 16, 1996
Peachtree City, GA 30269
Care Facsimile: (800) 843-1056
In the last two issues we have discussed compressor diagnosis. Once compressor diagnosis is complete, a
bad compressor must be replaced. As with any replacement part, the compressor should be an
Original Equipment Manufacturer (OEM) part or a manufacturer recommended substitute.
Hoshizaki offers a five year “parts only” warranty for the original compressor. In order to receive this
warranty, proper changeout and warranty filing procedures must be followed and the OEM part must
be used. Ask your local Hoshizaki distributor for these warranty procedure details. Warranty cannot be paid
if a non-OEM compressor is used ! The first step in a changeout is to evacuate the
system of all refrigerant. This refrigerant must be recovered using proper refrigeration practices as
required by the EPA. If the refrigerant is not contaminated, it may be recycled, cleaned and reused.
This is a judgment call that you should make for yourself and will depend on your recovery equipment capabilities.
You will find that some older models do not have a high side access port . In this case install a line tap valve on
the high side for use during the refrigerant recovery process. This line tap valve must be removed and
replaced with a sweat-on schrader access port once recovery is complete. On systems which have a liquid
line valve it is important to open the solenoid during recovery so that all of the refrigerant will be
recovered. This can be done by using a 115 volt cheater cord to energize the coil while recovering the refrigerant.
A compressor burnout will generally cause acid in the system. Acid has a distinct odor which will be
noticed when the system is accessed. Acid test kits which will confirm acid in the system are available from
your local wholesaler. Clean-up of a system containing acid will require more time and effort than a
basic evacuation for a compressor changeout. During the recovery process you will have time to
disconnect the compressor lead connections. First you should check to assure that the power is turned
off or that the unit is disconnected from the power supply. Then remove the terminal cover and inspect the
terminal connections. You will find in most cases, that the wires are marked C, R, & S at the terminal ends.
The general color code for KM compressor connections is black for common, red for run, and gray
for start. Check the unit wiring diagram for compressor wiring on other models. Make note of the proper
connections and disconnect the terminal ends. Also disconnect the crankcase heater on remote applications.
With the refrigerant removed from the system and the terminals disconnected, it is time to remove the old
compressor from the system. Disconnect the suction and discharge lines using proper refrigeration piping
practices. Care should be taken to assure that the system is not open for a long period of time. This will be
even more important in the future as new more hydroscopic alkylbenzene or polyolester lubricants
are used in new compressors. To protect against excessive moisture entering the system, plug the system
lines while you remove the existing compressor and place the new one into position.
Reconnect the compressor lines and solder a new schrader connection on the process tube.
Replace the liquid line drier with the correct OEM part. It is a good practice to cut out the existing drier
rather than using a torch to un-sweat it. This will eliminate the possible release of any moisture contained
in the drier back into the system. In the case of a burnout, you may deem it necessary to add a suction
line filter-drier especially designed to clean up a burnout. This filter-drier should be left in the system for one to
two weeks of operation and removed once the system is cleaned. An acid test can be used to verify a
clean system. The suction filter should be replaced and checked again in two weeks if the system is still
contaminated. The liquid line drier should also be replaced again at this time.
Add a little refrigerant to the system and leak check the new joints. Evacuate the system to 500 microns or
lower. A burnout system requires a triple evacuation. Pull the system down to 1500 microns
twice and once down to 500 microns or lower. Each time, break the vacuum with the refrigerant to be used in
the system to 2 psig or more. While you are waiting for the evacuation, reconnect the
compressor terminals and crankcase heater if used. Install any new start components supplied with the
compressor. It is a common practice to change the start components with a new compressor, especially if
the failure was electrical in nature. Double check your wiring against the wiring diagram to assure proper connections.
Once evacuated, charge the system weighing in the proper refrigerant amount and type according to the
name plate rating. Now you are ready to start the unit up and check it for proper operation.
UNIVERSAL KM FLOAT SWITCH
Have you noticed a difference in the KM float switches lately? The old drab black float switch is now
a bright white polystyrene material. Its the same basic reliable design using a new material. The new
float switch is manufactured for Hoshizaki by a company in Connecticut. The assembly line has been
installing the new float switch on units for around two months. Also, we are presently shipping the new float
switch out as a replacement part. You will find that there are two different types of float
switches on KM units in the field. A single stand pipe and a double stand pipe version are available as a
replacement part. The stand pipes connects either to a vent tube or to the pump out power flush line. The style
you need will depend on which model you are servicing. For a universal replacement that will fit any KM
model in the field, order the new part number 4A0086-01. This is a double stand pipe float switch.
To make it work on a single stand pipe unit , simply install it on the unit and cap the outside power
flush stand pipe. The protective caps included on a replacement drier # 427061-02 work perfectly for
this application. This idea should eliminate the necessity to stock two different float switches in your
inventory, saving time, cost, and space.
It is considered good refrigeration practice to change the liquid line drier any time a sealed refrigeration system
is opened for service. Hoshizaki recommends this practice when servicing our equipment.
The correct drier should always be ordered along with the refrigerant component that needs to be replaced.
OEM driers must be used, with only one exception. If you have a system contaminated with non-condensables
and no other system component needs replacing, it is acceptable to use a properly sized non-OEM drier from
your truck stock. This step will save time and effort on warranty repairs. Remember that this is the only
situation where use of a non-OEM part is acceptable.