Foster FCI20, F85, F20, F40, F60, FCI30, FCI85 Compressor, Water Pump Contactor Coil, Electronic Timer

11.Principle of Operation

11.1 How it works

In the cube ice makers the water used to make the ice is kept constantly in circulation by an electric water pump which primes it to the spray system nozzles from where it is diverted into the inverted mould cups of the evaporator. A small quantity of the sprayed water freezes into ice; the rest of it cascades by gravity into the sump assembly below for recirculation.

11.2 Freezing Cycle

The Hot refrigerant gas discharged out from the compressor reaches the condenser where, being cooled down, condenses into liquid. Flowing into the liquid line it passes through the drier filter, then it goes all the way through the capillary tube where, due to the heat exchanging action, it loses some of its heat content so that its pressure and temperature are lowered as well.

Next the refrigerant enters into the evaporator serpentine (which has a larger I.D. then the capillary) and starts to boil off; this reaction is emphasized by the heat transferred by the sprayed water.

The refrigerant then increases in volume and changes entirely into vapour.

The refrigerant vapour then passes through the suction accumulator (used to prevent any small amount of liquid refrigerant from reaching the compressor) and through the suction line. In both the accumulator and the suction line it exchanges heat with the refrigerant flowing into the capillary tube (warmer), before being sucked in the compressor and to be recirculated as high pressure, high temperature gas.

The freezing cycle is controlled by the evaporator temperature sensor (which has its probe in contact with the evaporator serpentine) that determines the length of the cycle first portion.

When the temperature of the evaporator serpentine drops to a pre-set value, the evaporator sensor probe changes its electrical resistance allowing a low voltage current (8-10 volts) to flow to the P.C. BOARD which in turn activates an electronic timer.

The timer, which is built-in the P.C. BOARD, takes over, from the evaporator temperature sensor, the control of the freezing cycle up to its completion.

NOTE: The change of the electrical potential of the evaporator sensor with the consequent activation of the timer (Time mode) is signalled by the glowing-up of the RED LED located in the front of the P.C. BOARD.

ATTENTION: In case, after 15 minutes from the beginning of the freezing cycle, the temperature of the evaporator sensor probe is higher then 0°C (32°F) (Shortage of refrigerant, inoperative hot gas valve, etc.) the P.C. BOARD switch OFF immediately the unit with the simultaneous blinking of the WARNING RED LED.

The length of the second portion of the freezing cycle is pre-fixed and related to the setting of the first four DIP SWITCH keys which is made in relation with the different unit versions.

The DIP SWITCH keys setting is made in consideration of the type of condenser used.

In Table B, page 18, are indicated the various lengths of the second portion of freezing cycle (Time mode) in relation to the different combinations of the DIP SWITCH KEYS.

In Table A, page 18, is illustrated the DIP SWITCH keys combinations for the different unit versions as they are set in the factory. The electrical components in operation during the freezing cycle are:

COMPRESSOR

FAN MOTOR (in air cooled version)

WATER PUMP

CONTACTOR COIL

and during the second phase of freezing cycle (Time mode) they are joined by the

ELECTRONIC TIMER

The refrigerant head pressure, in the course of the freezing cycle, ranges between 13.5 and 14.5 bars (190-205 psig) being controlled by the temperature sensor probe located within the condenser fins (Air cooled version) or, it is kept constant at 14 bars (195 psig) by means of the water regulating valve (water cooled version).

On the air cooled version, the condenser temperature sensor, when senses a rising of the condenser temperature beyond the pre-fixed limit, changes its electrical resistance and send a low voltage power signal to the Micro Processor of P.C. BOARD which in turn energizes, through a TRIAC, the FAN MOTOR.

When the opposite situation occurs, i.e. the condenser temperature gets below the pre-fixed limit, the temperature sensor changes again its electrical resistance reducing therefore the current flow to the P.C. BOARD to cause the fan motor to temporary cut-off.

NOTE: In case the condensor temperature probe senses that the condensor temperature has rised to 70°C (160°F) - on air cooled versions

-or 62°C (145°F) - on water cooled versions - for one of the following abnormal reasons: CLOGGED CONDENSOR (Air cooled version)

FAN MOTOR OUT OF OPERATION (Air cooled version) INSUFFICIENT FLOW OF COOLING WATER (Water cooled version) AMBIENT TEMPERATURE HIGHER THEN 40°C (100°F)

it causes the total and immediate SHUT-OFF of the machine in order to prevent the unit from operating in abnormal and dangerous conditions. When the ice maker stops on account of this protective device, there is a simultaneous glowing of the RED LED, warning the user of the Hi Temperature situation. After having eliminated the source of the condensor hi-temperature, to restart the machine it is necessary first, to rotate for a while the program selector on RE-SETposition then, to rotate it again on OPERATION position.

The same can be done by just switching OFF and ON the unit at main line switch.

The ice machcine resumes its normal operation by going through the 5 minutes water filling phase.

At the start of the freezing cycle the refrigerant suction or lo-pressure lowers rapidly to 3.3 bar-45 psig then it declines gradually - in relation with the growing of the ice thickness - to reach, at the end of the cycle, approx. 1 bar -14 psig with the cubes fully formed in the cup moulds. The total length of the freezing cycle ranges from 15-18 minutes.

11.3 Defrost or Harvest Cycle

As the electronic timer has carried the system throughout the second phase of freezing cycle, the defrost cycle starts.

ATTENTION: In case the unit is be able to reach 0°C (32°F) evaporating temperature within 15 minutes, or after 45 minutes from the beginning of the freezing cycle it has not yet reached the evaporator temperature of -15°C (5°F), the machine goes straight into the defrost cycle omitting the timed portion of the freezing cycle related to the setting of the first four DIP SWITCHES.

NOTE: The length of the defrost cycle is pre-determined by the setting of the DIP SWITCH KEYS NO. 5, 6 and 7 and it is related as well to the

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