NZ236585A - Ice cube maker: condenser temperature controls compressor and condenser fan - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £36585 236 5 PrUsi'ty Cora}.v"r<"~ j , choc , b.4,.(.asaas!.^.. i ! a.^osal ,og, mwr\m . * { '* '*•'A* " 1 • Under the provisions of Regulation 23 (1) the ....

Specification hes been ante-dated to 19 .&L DIVIDED FROM: No.: 224054 Date: 28 March 1988 NEWZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION ICE CUBE MAKER WITH NEW FREEZE AND HARVEST CONTROL X/ We, SCHNEIDER METAL MANUFACTURING COMPANY, an Iowa Corporation of 2421-15th Street Southwest, Mason City, Iowa 50401, United States of America hereby declare the invention for which I / we pray that a patent be granted to me/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 23 6 5 6 BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention pertains to a method of making ice cubes having new steps of control, and to an ice cube maker having a new and improved control for harvest and freeze cycles, and to this control for an ice cube maker.

An ice cube maker having a vertical flat plate gridded evaporator is well known and is in extensive public use. The food and beverage retailers and in particular the fast food chains and restaurants have a significant preference for this type of ice cube maker. It is commercially accepted and in many instances preferred.

The leading example of this general type of ice cube maker is made by The Manitowoc Company, Inc. of Manitowoc, Wisconsin, and is quite well documented in U.S. Patent 3,430,452 of March 4, 1969.

Another example of this type of cuber is made by Mile High Equipment Company of Denver, Colorado and is documented in U.S. Patent 4,341,087 of July 27, 1982. This patent has an extensive discussion on the merits of this general type of ice cube maker.

Despite the commercial acceptance and preference for this type of ice cube maker, there have been problems with the control of the freezing and harvest cycles, amongst other things.

Typically, this type of ice cube maker will be in a freeze cycle for 8-12 minutes and will then switch to hot gas defrost to loosen the cubes from the evaporator so that the cubes can be ejected from the evaporator. Timer controls do not work well because the specific incoming water temperature, line voltages, and ambient temperatures are unpredictable.

Many various schemes of control have been tried and found to still give problems.

Most recent examples of a controls for this type of machine have been developed by Manitowoc and are disclosed in U.S. Patent 4,'480,441 of November 6, 1984 and U.S. Patent 4,550,572 of November 5, 1985. The first is an electro-mechanical device and is thought to be commercialized but the second device has not been seen on Manitowoc products.

Other patents having ice cube makers of this general type include: the following United States patents: THE PRIOR ART 3,913,349 3,964,270 3,144,755 Johnson Dwyer Katti s JAT/1752M ? 3 6 5 8 5 OBJECTS OF THE INVENTION It is an object of the present invention to provide an ice cube maker with an improved condenser fan control.

It is a further object of the invention to provide an ice cube maker with an approved compressor safety control.

SUMMARY OF THE INVENTION According to the principles of the present invention, an ice cube maker has: a) an ice making refrigeration system having a compressor, condenser, condenser fan, evaporator plate, water reservoir, water pump for pumping water in the reservoir over the plate, hot gas defrost valve, and means for control of the defrost valve; b) temperature sensor means for sensing the temperature of the condenser; c) first control means operatively connected to said sensor means for turning the condenser fan off when the condenser is at a temperature below a predetermined low temperature value; d) second control means operatively connected to said sensor means for turning the condenser fan on when the condenser is at a temperature above a predetermined middle temperature value; and e) third control means operatively connected to said sensor for shutting off the compressor when the condenser temperature exceeds a predetermined maximum operative temperature value. 17 AUG 1332 >36585 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational sideview, in partial section, showing the preferred embodiment of the ice cube maker of the present invention; FIG. 2 is a similar elevational side view of the evaporator and ice curtain componentry of the structure of FIG. 1 with the curtain open; FIG. 3 is a downward looking sectional view through lines 111-111 of FIG. 1; FIG. 4 is an elevational sectional view through line IV-IV of FIG. 1; FIG. 5 is a schematic of the ice maker refrigeration system; and FIG. 6 is a logic diagram for the electrical control of the ice cube maker of FIG's 1 and 5.

AS SHOWN IN THE DRAWINGS The principles of the present invention are embodied in and practiced with the preferred embodiment of an ice cube maker such as is shown in FIGS 1 & 2 and which is generally indicated by the numeral 10.

The ice maker 10 has an evaporator generally indicated by the numeral 11 which preferably has a freezing plate 12 made of a generally vertical flat metal plate having top, bottom and side flanges and an internal egg crate type matrix with vertical dividers 13 and horizontal dividers 14 dividing the freeze plate 12 into small discrete pockets for the freezing of discrete cubes. On the rear side of the freeze plate 12 is a £$6 5 refrigerant coil 15 which is appropriately serpentined on and over the plate 12. A temperature thermister well 16 is soldered to the rear side of the freeze plate 12 just above the vertical mid point of and on one transverse side of the freeze plate 12. The refrigerant coil 15 and thermister well 16 are spaced from each other and are both thermally enclosed within a backing of thermal insulation 17. A circulation pump 18 for the water to be frozen into ice cubes has an inlet line from a water catching reservoir 19 and an outlet line to a distributor manifold 20 mounted on the top of the evaporator 11. A movable evaporator curtain 21 is pivotally suspended from a horizontal axis fulcrum 22. The curtain 21 and fulcrum 22 are in front of the evaporator 11 and the fulcrum 22 is adjacent to and above a mid level of the evaporator 11. The curtain 21 is normally closed during freezing of ice, as is shown in FIG. 1, and the curtain 21 is opened by falling ice during harvest as is shown in FIG. 2 The curtain 21 retains falling water upon the freeze plate 12 and during circulation of water over the freeze plate 12 during freezing of ice the curtain 21 directs the falling water into the reservoir 19 from which the pump 18 continually recirculates the water over the freeze plate 12 during the freeze cycle. At the start of a freeze cycle, the reservoir 19 is filled with water and the fill level is controlled by a float valve 23. The pump 18 is turned on and water from the reservoir 19 is then continuously circulated through the manifold 20 and from there downwardly by gravity over the freeze plate 12. The curtain 21 confines the falling water and directs it back into the reservoir 19. When freezing of ice is completed, the ice maker 10 switches into hot gas defrost and releases the frozen ice from the freeze plate 12. The frozen ice looks like a waffle with individual discrete cubes being attached to each other by a thin sheet of ice frozen over the outer edge of the dividers 13, 14. The falling ice forces the curtain 21 to open and the ice falls past the water reservoir 19 and into an ice bin (not shown) below the reservoir 19. The waffle ice sheet then breaks up leaving discrete cubes.

An important feature of this invention is the curtain position sensor generally indicated by the numeral 24. Movement and position of the curtain 21 are sensed and utilized to control shut-off of the ice maker 10 when the bin is full of ice cubes, and to restart the freeze cycle upon completion of a harvest of ice cubes. The curtain position sensor 24 is mounted to the ice maker 10 above the curtain 21, and the freeze plate 12 and the water manifold 20 whereby the position sensor 24 is isolated from and spaced above the moving water and ice. The curtain position sensor 24 JAT/1752M -5- 23 6 5 has an electronic curtain sensor 25 which is preferably an integral U-shaped photo electric emitter and receiver (PER) having a constantly energized emitter. The sensor 25, a sensor bracket 26 and a flag fulcrum 27 are mounted to the ice maker and fixed with respect to the evaporator 11 and the curtain fulcrum 22. A movable sensor flag 28, which is preferably a first class lever, is pivotally mounted in the sensor fulcrum 27. The flag 28 is freely pivotable and is a flat piece of sheet metal having a weight 29 which by gravity biases the flag clockwise as shown in FIGS. 1 & 2 into normal abuttment against a flag stop 30 on the bracket 26. The flag 28 has a small precisely located open sensor aperture 31 which normally is precisely registered with and which is between the emitter and the receiver of the sensor 25. The sensor aperture 31 is within the flag 28, and the aperture 31 and weight 29 jointly form a precision shutter for momentary obstruction of the beam from the emitter to the receiver of the sensor 25. The curtain 21 has a sensor cam 32 which contacts against and drives a cam follower 33 on the flag 28. The cam 32 is normally spaced from and does not contact the follower 38 and has a lost motion connection which enables the curtain 21 to flop around without effecting the sensor 25. When the ice maker 10 is freezing ice, the curtain 21 is closed as shown in FIG. 1 and the sensor 25 is normally transmitting from its emitter to its receiver through the flag sensor aperture 31. When the ice maker 10 releases its cubes from the freeze plate 12, the cubes fall down and force the curtain 21 open as shown in FIG. 2. When the curtain 21 opens, the curtain cam 32 contacts the follower 33 and cams the flag 28 counterclockwise to the alternative position shown in FIG. 2. As soon as the flag sensor aperture 31 is lifted, the opaque flag 28 obstructs the beam of the sensor 25 and the sensor provides a signal indicative of this obstruction to an ice maker control 34. The control 34 then makes the assumption that cubes are being harvested. After the ice falls past the curtain 21, the curtain 21 recloses by gravity and the flag 28 is releasd and it returns to its normal position whereupon the beam of the sensor 25 again becomes' normally transmitted. When the beam is broken during opening of the curtain 21, the refrigeration system is immediately switched from hot gas defrost to cooling. If the ice bin has been filled with cubes, the harvest will not fall completely past the curtain 21 and the curtain 21 will be held open. When this happens the beam of the sensor 25 is obstructed for an abnormally long time period and if transmission of the beam is not re-established, the ice maker 10 deduces it has filled its storage bin and it shuts itself off. A self-resetting curtain timer 40 receives the signal that the JAT/1752M -6- 2 3 6 5 b curtain 21 is open and if the curtain 21 stays open for an excessive period of time, the timer 40 provides a signal to shut down the compressor 35 and other componentry. The timer 40 will provide a turn-off signal after the curtain 21 has been open too long. When the ice level in the bin falls and the curtain 21 closes and transmission of the beam of the sensor 25 is re-established, the ice maker 10 automatically starts itself. The entire curtain position sensor 24 is well above both the water and ice and is not subject to contact with the water or ice The position sensor 24 is also located far above the storage bin and it will operate regardless of what configuration of storage bin is utilized. The sensor 24 also works on very low signal voltage and current and does not bring any type of a potentially hazardous electrical potential into the ice making and storage chambers. This sensor 24 has no springs and nothing to wear out or break. It is extremely reliable, low cost, and accessible, and is easily understood by people who own, operate, repair or rely upon the ice maker 10. What electrical potential and signals are provided or made by the sensor 25, are completely isolated from contact with either ice or water. The termination of hot gas defrost function and the function of shut-off when the storage bin is filled are responsive to a clear mode change of the sensor 25 from transmitting to obstructed and vice-versa. The lost motion connection between the curtain 21 and flag 28 enables the curtain 21 to partially move without signaling ice release when the ice cubes have only partially released from the freeze plate 12. The ice maker 10 waits for the harvest completion signal until the complete sheet of ice and cubes falls off of the freeze plate 12 and substantially opens the curtain 21.

As an example, the curtain 21 will open 5 to 10 degrees before the cam 32 engages the follower 33. The curtain 21 will then, upon dropping of the ice sheet, open a total of about 20 degrees and in the last 10 degrees of travel the flag 28 will be turned about 30 degrees. The angular mechanical motion amplification between the curtain 21 and flag 28 is at least 2:1 and preferably about 3:1 as soon as the cam 32 and follower 33 engage each other. During the mode changes from freeze to defrost and back to freeze, the compressor 35 runs continuously and there is no stop or start which greatly enhances compressor life and control component life as well as providing for increased thermal efficiency and ice production.

Another important improvement in this ice maker 10 is a new freeze control, previously identified in general by the numeral 34. The control 34 is responsive to the curtain position sensor 24 and is connected to control the water circulation pump 18, the refrigeration compressor 35, the JAT/1752M -7- 23 4** hot gas defrost valve 36, the condensor fan 37, and other componentry as will be further described. A freeze plate temperature sensing thermister 38 is mounted in the freeze plate thermister well 16 is operatively connected to the control 34. Within the control 34 is a self-resetting refrigeration delay timer 39, which may have either a fixed or variable delay as circumstances dictate. During freezing of ice on the freeze plate 12, the thermister 38 will electronically indicate the temperature of the freeze plate 12. The freeze plate 12 temperature has been determined to be analogous to the size of ice as a function of the thickness of the ice upon the freezing plate 12 of the evaporator 11. When the thermister 38 indicates the plate 12 temperature to be at or below a predetermined temperature, the delay timer 39 is started. If the indicated temperature remains at or below the predetermined temperature for the delay timer period, the timer 39 will complete a countdown of the delay time period and upon completion of the countdown the timer 39 will provide a signal that freezing of a batch of ice cubes has been completed. The control 34 will then switch the ice maker 10 into hot gas defrost for harvest of the ice. If during the freeze cycle, the temperature indicated by the thermister 38 merely momentarily dips down to or goes below the predetermined temperature and then returns to above the predetermined temperature, the timer 39 terminates its countdown upon the indicated temperature rising above the predetermined temperature and the timer 39 then discharges and resets itself to relative zero. When the temperature of the freeze plate 12 subsequently falls to the predetermined temperature, the countdown will again be started. This start, terminate, erase or reset, and restart of the countdown can be done as many times as needed. Typically and usually, it will be done only once. When the termination and reset is done, false harvests of incomplete ice are prevented.

A predetermined temperature in the range of 2-12 degrees Fahrenheit (-17 to -11 degrees Celsius) or 7 + 5 degrees Fahrenheit (-14 + 3 degrees Celsius) has been found to be indicative of the proper size and quantity and thickness of ice upon the freeze plate 12 for complete harvest of a proper quantity of properly completed and sized ice cubes. A countdown time period in the range of 20-30 seconds has been found to prevent false or improper harvests of ice. The freeze cycle of the refrigeration systems continues without interruption during the countdown period and the hot gas defrost is initiated immediately upon completion of the countdown.

The water pump 18 and water circulation over the freeze plate 12 are continued during the countdown. Upon completion of the countdown, the pump JAT/1752M -8- 23 6 5 18 and water circulation are immediately shut down and terminated concurrent with start of the hot gas defrost. The ice on the freeze plate 12 is thereby prevented from excessive sub-cool and the ice is released from the freeze plate 12 in the shortest possible time. The hot gas defrost start and the termination of the water flow over the freeze plate 12 are both done immediately upon completion of the countdown.

FIG. 6 has a logic diagram of the ice maker control 34. Line power for the ice maker 10 comes in through a manually operable on/off switch 50 and through a main relay 51 to the compressor 35 and other operating components. Low voltage DC power before for the control 34 and sensor 25 comes in line 42 and is ta-ken off line power before the oh/off switch 50. The signal from the freeze plate thermister 38 is fed through an adjustable potentiometer 41 and then through an amplifier 52 to the refrigeration delay timer 39. The timer 39 as previously described, has a countdown period of about 20-30 seconds. Start of the countdown period can be adjusted with the potentiometer 41 to give larger or smaller ice cubes.

Upon completion of its countdown, the timer 39 sends its signal to a harvest amplifier 53. The harvest amplifier 53 sends its signal to the hot gas defrost 36 and the water pump 18, to a control turn-on timer 54, and to a latching interlock amplifier 55. The signal to the hot gas defrost 36 simultaneously turns on the hot gas defrost 36 and turns off the water circulation pump 18. The interlock amplifier 55 feeds a signal out a signal line 56 to a harvest period timer 57. When the amplifier 53 interlock 55 are latched, the hot gas defrost 36 is on and the water pump 18 is off.

The signal from harvest amplifier 53 to the control timer 54 disables the timer 54 and the control amplifier 75 whereupon via signal line 66 an appropriate signal is provided to immediately disable the freeze plate temperature amplifier 52, a suction line temperature amplifier 67 and a water temperature amplifier 68 so that the control 34 does not receive signals from amplifiers 52, 67 or 68 during hot gas defrost and during initial pulldown of the subsequent freezing cycle as will be described.

When the curtain 21 is subsequently opened by falling ice, the curtain sensor 25 sends its signal that the curtain 21 has opened via signal line 58 to simultaneously unlatch the harvest amplifier 53 and the interlock amplifier 55. Immediately the hot gas defrost 36 is turned off and the pump 18 restarted and a subsequent freeze cycle is started. The signal that the curtain 21 has opened is also sent from the curtain amplifier 59 to the curtain timer 40. If the signal to the curtain timer JAT/1752M -9- 23 6 5 40 is provided for a length of time in excess of the timer 40 preset period, the curtain timer 40 sends an output signal to a full bin amplifier 60 which then provides a signal via signal line 85 to turn off the refrigeration as will subsequently be described.

The harvest period timer 57 is started simultaneously with the hot gas defrost 36. The harvest period timer 57 will have a predetermined countdown period, with a 4 1/2 minute countdown period being an appropriate example. The curtain timer 57 will countdown if the curtain 21 does not open and upon completion of a countdown will indicate no harvest or a faulty harvest and that something is wrong with the ice maker 10. Upon completion of a countdown,- the harvest period timer 57 will send a signal to latch a faulty harvest amplifier 62 which in turn will send a signal out signal line 63 to shut off the refrigeration.

When the signal from the harvest amplifier 53 is changed upon start of the next freeze cycle, the contol timer 54 is started. The control timer 54 has a countdown period that is greater than the initial pulldown time of the refrigeration system and greater than the time it takes to begin freezing ice on the freeze plate 12. The control timer 54 countdown time will preferably be more than one-half of the time it takes to complete freezing of a normal cycle of ice cubes. A preferred and an example time for countdown of the control timer 54 is about six minutes. When the control timer 54 has completed its countdown, it sends out signals by its control amplifier 75 and signal lines 66 that simultaneously enable thermister amplifiers 52, 67 & 68 and therefore the thermisters 38, 64 & 65. If the suction line temperature is too high, specifically greater than forty degrees Fahrenheit, a signal will then be sent by suction line thermister 64 and suction line amplifier 67 via signal line 84 to shut down the ice maker 10. The water temperature thermister 65 is positioned to sense and indicate the temperature of the water being circulated over the freeze plate 12 by the pump 18. If the indicated water temperature is then too high, for example greater than 45 degrees Fahrenheit, the water thermister 65 and water temperature amplifier 68 will send a signal via signal line 69 to cause shutdown of the ice maker 10. The amplifiers 52, 67 & 68 are disabled during hot gas defrost and pulldown, and are then enabled by the control timer 54 and amplifier 75 after the refrigeration system has stabilized in a freeze cycle.

A refrigeration condensor temperature thermister 70 senses and indicates condensor temperature to a pair of condensor amplifiers 71, 72. The first condensor amplifier 71 is operatively connected to send a signal JAT/1752M -10- 236 to turn off the condensor fan 37 if and when the condensor is too cold. The output signal line 56 of the harvest cycle latching interlock 55 is also connected to an input of the first condensor amplifier 71 so that a signal to go into hot gas defrost also turns off the condensor fan 37 and keeps the fan 37 turned off during hot gas defrost. The second condensor amplifier 72 discretely sends a signal to latching condensor amplifier 73 which in turn sends a signal via signal line 74 to shut down the ice maker 10 when the condensor temperature is too hot. The first condensor amplifier 71 will, as an example, keep the condensor fan 37 turned off if the condensor temperature is too low. When the condensor temperature goes above 105 degrees Fahrenheit, the first amplifier 71 will cause the condensor fan 37 to turn on; and when the condensor temperature drops below 85 degrees Fahrenheit, the first amplifier 71 will cause the condensor fan 37 to turn off. The second condensor amplifier 72 will shut down the ice maker when the condensor temperature reaches 155 Degrees Fahrenheit; such a high temperature is indicative of a dirty condensor, fan motor failure, fan jammed, or plugged air inlet.

A shut down inverter 76 has an output signal line 77 operatively connected to open the main relay 51 and disable the compressor 35 and other operating components of the ice maker 10. The shut down inverter 76 inputs are connected with OR logic wherin any single input will effect shut down of the ice maker 10. A shut down signal from curtain timer 40 via signal line 85, or faulty harvest amplifier 62 via line 63, or in condensor temperature signal line 74 will cause shut down inverter 76 to open the relay 51. The suction temperature signal line 84 is connected into suction temperature inverter 78. If the suction temperature is too high, for example above 40 degreed Fahrenheit, and the suction amplifier 67 has been enabled, something is wrong and a signal will be sent to the suction inverter 78 which in turn will send a shut down disable signal via signal line 79 to the shut down inverter 76.

The water temperature signal line 69 sends a signal after the water temperature amplifier 68 has been enabled, and when the water is too warm to water temperature inverter 80 which in turn sends a disabled signal to the shut off inverter 76 via signal line 81.

If the curtain 21 failed to close, the signal in line 61 is sent to a multiple ice maker full bin inverter 82, the signal from the full bin amplifier 60 is sent via signal line 85 and signal line 88 to the shut down inverter 76 for causing shut down of the refrigeration until the curtain 21 reopens. The curtain open signal is also sent via signal line 85 and JAT/1752M -11- 236 5 connector pin 86 to any upper level ice makers (not shown) atop of the subject ice maker 10. An upper level ice maker will eventually return an upper curtain open signal via connector pin and signal line 87 to full bin inverter 82 which in turn sends a shut down signal via line 83 to the shut down inverter 76 which will effect a shut down of the subject ice maker 10 and all upper level ice makers.

Thus, a disable signal in any one of signal lines 63, 74, 79, 81, 83, 85, or 88 will cause the shut down inverter 76 to open the relay 51 and stop the compressor 35. The outputs of the inverters 76, 78, 80, 82, the condensor latching amplifier 73, the control amplifier 75, and the interlock amplifier 55 are all discretely connected to a priority encoder 89 which has its outputs connected to a decoder driver 90 which has its outputs connected to a status display 91 prferably of the digital LED type.

The status display 91 gives a visual indication of what the ice maker 10 is doing, and why. For example, the following read outs indicate the followi ng.

INDICATED STATUS NUMBERS 0 EXPLANATION Unit is in freeze cycle, making ice no problems.

Uni t i s harvest cycle, ice should drop shortly no problems.

Normally indicates a full bin condition, unit off, water curtain being held open with ice.

Unit off due to circulating water temperature not pulling down to at least 45°F.

POSSIBLE CAUSE 2 If "2" is shown but bin isn't ful1, check for individual cube holding curtain open.

Incoming water shut off. Pump not running or plugged. Reservoir leaking badly.

Water level set too hi gh causi ng premature syphoning. Sensor not insulated properly. Defective sensor. 3 Manual reset required.

JAT/1752M 236 5 cont...

INDICATED STATUS NUMBERS Decimal point OFF EXPLANATION Unit off due to suction line not pulling down to at least 40°F.Manual reset required.

Unit off due to ice not releasing from evaporator within four minutes after entering harvest cycle. Manual reset required.

Unit is off due to condensor temperature climbing too high. Manual reset required.

Indicates that all sensors, except condensor, are switched off for first six minutes of freeze cycle.

POSSIBLE CAUSE Low on refrigerant. Defective refrigerant valve. Compressor defective or inefficient. Defective power relay won't close.

Defective start relay, won't start compressor. Low voltage to compressor no start.

Defective compressor valve.

Defective sensor.

Sensor not insulated properly.

Water curtain jammed and won't swing open. Defective hot gas valve won't open, piugged. Ice slab deformed, won't release properly. Extremely low ambient temperature, below 45°F.

Dirty condensor.

Defective fan motor or blade.

Gross overcharge. Extremely high ambient temperature, above 120°F Defective sensor.

Normal time delay, approximately 6 minutes.

JAT/1752M 2365 cont...

INDICATED STATUS NUMBERS EXPLANATION Indicates all sensors have been swi tched on.

Indicates evaporator temperature has pulled down and unit will go into harvest after time delay.

POSSIBLE CAUSE Decimal point ON Decimal point Normal time delay of approximately 20 seconds before harvest cycle begi ns.

FLASHING If and when manual reset is required, the master switch 50 must be turned off for 10 seconds and then returned to "ON".

This new and improved ice maker 10 is extremely reliable and commercially effective. It is relatively simple and fool proof. It reliably harvests ice cubes and reliably starts and/or shuts itself off. When something is wrong it stops before destroying itself and it indicates what's wrong.

Although other advantages may be found and realized and various modifications may be suggested by these versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon, all such embodiments as reasonably and properly come within the scope of our contributions to the art as defined by the following claims.

Claims (6)

WHAT WE CLAIM IS:

1. An ice cube maker, comprising: a) an ice making refrigeration system having a compressor, condenser, condenser fan, evaporator plate, water reservoir, water pump for pumping water in the reservoir over the plate, hot gas defrost valve, and means for control of the defrost valve; b) temperature sensor means for sensing the temperature of the condenser; c) first control means operatively connected to said sensor means for turning the condenser fan off when the condenser is at a temperature below a predetermined low temperature value; d) second control means operatively connected to said sensor means for turning the condenser fan on when the condenser is at a temperature above a predetermined middle temperature value; and e) third control means operatively connected to said sensor for shutting off the compressor when the condenser temperature exceeds a predetermined maximum operative temperature value.

2. The ice-cube maker of claim 1, including an electronic diagnostic circuit operatively connected to said sensor means, said circuit having means for visually indicating that the condenser temperature is below the predetermined low temperature value.

3. The ice cube maker of claim 1 or claim 2, including an electronic diagnostic circuit operatively connected to said sensor means, said circuit having means for visually indicating that the condenser temperature is between the predetermined low temperature value and the predetermined maximum temperature value.

4. The ice cube maker of any one of claims 1 to 3, including an electronic diagnostic circuit operatively connected to said sensor means, said -15- circuit having means for visually indicating that the condenser temperature is above the predetermined maximum temperature value.

5. The ice cube maker of claim 1, including an electronic diagnostic circuit operatively connected to said sensor means and said first, second and third control means, said circuit having a single indicator for visibly indicating that: (1) the condenser temperature is below the predetermined low temperature value, (2) the condenser temperature is between the low and the maximum predetermined temperature values; or (3) the condenser temperature is above the maximum predetermined temperature value.

6. An ice cube maker as claimed in claim 1 and substantially as herein described with reference to any embodiment shown in the accompanying drawings. -16- 23 6 5 8 5 r> o xzr JlgS ^Jlg-5 I " 2Z. /6J8 .^cJUr^ucle/. ...M&laJl.. By £ue-/their authorised ag§,nt ^ "" A. J PARK & SOf Psr^j,- o ) MAIN RELAY ON/Off - Jig,6 fK> CM CD cn CO