Abstract: A transport refrigeration unit powered by a two speed prime mover and having the capability of providing at least four modes of operation is controlled by an arrangement as shown in FIG. 2 which provides for operation in either a continuous cycle in which the prime mover runs continuously to provide the modes shown in FIG. 3 or, alternatively, operates in a start-stop cycle to provide the modes of operation shown in FIG. 4. The control in both of the cycles of operation provide for delays in the change of speed from low to high upon certain departures in temperature from one temperature band to another band which would normally call for high speed operation.

Abstract: An electronic circuit for controlling the heating or air conditioning apparatus in an automobile permits the capability of heating the vehicle without the heat surges which can occur after short periods of ignition turn off and permitting manual on-off control of the heating system even if the thermostat fails. A second circuit for controlling the device activating the valve controls the flow of heating or cooling medium independently of the ignition switch and contains a timer to keep the valve closed for a predetermined time after ignition switch-off. Two limit switches are also present for permitting the valve to be set at an open or closed position independently of both the ignition switch and the timer.

Abstract: An energy management system for a chilled product vending machine for controlling the cycling of the refrigeration system therefor and the ON-OFF status of the machine is described. The energy management system includes a microcomputer for controlling the above-described cycling and ON-OFF functions. A hand-held programmer is provided to input machine ON-OFF times to the microcomputer, the ON times defining sales periods. The microcomputer has data stored therein related to cooling characteristics of different types of machines which may be selectively accessed by manually-actuated selector switches. This enables retrofitting of the energy management system into various types of vending machines. The energy management system also provides increased cooling during high volume sales periods, morning warm-up prior to the beginning of a sales period, periodic continuous cool-downs to maintain acceptable product temperatures, and continuous cool-down following individual vends during a non-sales period.

Abstract: An equipment protector and energy saving apparatus includes transient protection as well as under voltage protection by preventing the reduced voltage from being applied to motors and other apparatuses that may be damaged because of insufficient voltage being applied thereto. Provision is incorporated to protect for momentary low voltage transients and turn-on prevention, if the line voltage should be reduced below a predetermined value. Provision is also made for correcting for a small increase in line voltage which may occur when the operating equipment is removed from the line. A timing device may be incorporated therein in order to remove the protected equipment from the line for predetermined intervals of time.

Abstract: An electronic thermostat operative to be connected to a furnace or other temperature modifying apparatus, to control its state of operation, includes means for generating a desired temperature set point signal and means for measuring ambient temperature on the thermostat. When the ambient temperature falls below the set point the furnace is energized for a predetermined period of time. The time of energization is increased or decreased by a small increment after each heating cycle depending upon magnitude of the temperature increase which occurred at the thermostat as a result of the heating cycle in order to adaptively achieve a predetermined temperature increase during the heating cycle and the thermal overshoot period which occurs following de-energization of the furnace.

Abstract: In a method for controlling an air conditioning system including a frequency-variable power source device for providing an AC electric power of a variable frequency, and a compressor driven by the AC electric power, the air conditioning power of the conditioning system being dependent on the frequency of the AC electric power, the temperature of the air to be conditioned is detected; and a frequency set value is determined in accordance with a deviation of the detected temperature with reference to a set temperature. For determining the frequency set value, a plurality of temperature deviation zones are defined; the frequency set value is changed when the deviation transits from one of the zones to another; and the frequency set value is also changed when the deviation continues to be within one of the zones of a relatively great deviation over a predetermined length of time.

Abstract: A method and apparatus for proving a demand for air conditioning or heating upon startup of an air conditioning unit before the unit is allowed to effect heat transfer. A separate thermal sensing unit is provided in the return air to prove a demand for cooling prior to the conventional thermostat of the unit being energized to operate the unit in the normal manner. This method and apparatus prevents energy waste and unnecessary cycling at startup and low load conditions.

Abstract: On an automotive vehicle having a stick-shift transmission, the air conditioner is turned off when the driver closes a switch in the handle of the gear shift lever to turn on an ultrasonic transmitter. A timer keeps the air conditioner off, following the signal from the ultrasonic transmitter, for a time interval long enough for the driver to shift through the lower gears and into high gear.

Abstract: A motor control system includes a motor system having a pole-amplitude-modulated (PAM) motor, a motor breaker, and a speed switch coupled between the motor breaker and the PAM motor. The PAM motor is coupled to a fan in an exhaust duct having a controlled damper for controlling air flow therethrough. A control system step logic sequencer includes means responsive to permissive signals for providing in sequence control signals to the motor breaker and speed switch in response to confirmation signals received from the motor breaker, the speed switch and the PAM motor.

Abstract: In a compressor protective switch system for the refrigerant compressor of the refrigeration system of an automotive air conditioner, a pressure sensitive switch adapted to be open in response to a refrigerant pressure lower than a relatively high predetermined value is paralleled by a positive temperature coefficient (PTC) resistance element or a series combination of a PTC resistance element and an atmospheric temperature sensitive switch adapted to be open in response to an atmospheric temperature lower than a predetermined value.

Abstract: A protecting device for protecting a refrigerant compressor from overheating or seizure caused by a shortage of refrigerant by any chance such as leakage thereof. The device includes a temperature sensor disposed on the outer wall of the compressor casing in the vicinity of a refrigerant intake suction suction port for sensing the temperature of the outer wall to output the sensed or measured data and a discriminator for discriminating an occurrence of refrigerant shortage by an excess of the data over a predetermined condition for comparison. The signals from the discriminator cause a warning issuance of the refrigerant shortage or an automatic stoppage of the compressor operation.

Abstract: An air conditioner system for sensing and controlling the temperature in the compartment of an automotive vehicle to an established desired temperature includes an over-correction means whereby the vehicle compartment temperature is temporarily increased to exceed the desired temperature and the temperature rise is terminated after the sensed temperature has attained or nearly attained the desired temperature. When the sensed temperature rises so that the difference between it and the desired temperature exceeds a reference value, the corresponding correction signal is generated and correction is applied repeatedly so as to make the difference less than the reference value and thereby to attain the desired compartment temperature.

Abstract: The timer circuit of the present invention comprises a comparator, which, in the example of the air conditioner, compares the room temperature measured by a thermistor with a predetermined value and charges the timer capacitor of the timer circuit when its output is in ON state, and makes the capacitor discharge when its output becomes in OFF state; thereby the timer circuit can produce the first set time, for example, by the abovementioned discharging time, in this first set time a compressor circuit being made OFF for prevention of overloading due to a too-early restarting, and furthermore, with utilizing the same timer circuit with a modified predetermined value of the comparator thereby producing subsequent cycles of charging and discharging and accumulating a predetermined number of repetition of the cycles, a desired longer time for the second time can be produced.

Abstract: Method and apparatus for monitoring a plurality of thermal parameters and the pressure related work load of a motor-compressor unit utilized in a heat pump system and providing protection for the motor-compressor by turning off the system for time periods dependent upon which parameter caused the system to be turned off.

Abstract: A frost sensor circuit which employs a thermistor (10, 20) to sense the amount of frost present on the cooling coils of a refrigerator, air conditioner, or the like, and to inhibit defrosting that would otherwise occur at regular intervals, in those cases where the frost present is not enough to justify a defrost function thereby to limit defrost heating to those cycles requiring it, thus saving electrical energy. This is done by mounting the thermistor at or on the coils to collect the same amount of frost as the coils and to have the defrost cycle control (11) energize the same for a timed interval, melting the frost thereon and thereby determining the amount of frost build-up.

Abstract: A defrost system for refrigeration units, particularly heat pumps, is described. Features include means for initiating a defrost cycle upon the concurrence of two sensed conditions, and terminating the defrost cycle either on the lapse of a determined time interval or the occurrence of a sensed condition, whichever occurs first. Delay timer means prohibits consecutive defrost cycles or a defrost cycle upon restoration of power in the event of a power failure. Means are also provided permitting short cycle testing of the system.

Abstract: A refrigerator includes a compressor, a condenser fan, and an evaporator fan simultaneously energized by a temperature control system which includes a thermistor located to sense the average temperature of the cabinet air and a potentiometer manually adjustable to a desired temperature set point. The on or run time of the compressor and fans is controlled by the thermistor sensed temperature with respect to the set point. The duration of the run time is measured by a resettable counter. The off time is adaptively controlled within a predetermined range which minimizes energy consumption while maintaining good temperature control. An off time counter, which is used to determine the duration of the off cycle, is incremented when the measured run time is less than a desired minimum, is decremented when the measured run time is greater than a desired maximum, and maintains the prior off time when the measured run time is within a desired range.

Abstract: A circuit is described in which a triac is to be fired to allow voltage to be supplied to start a motor which powers the compressor of a refrigerator. In order that the triac is fired at zero-crossings of the voltage, the voltage is supplied to two comparators which are connected antiparallel with one another, and which are supplied with a reference voltage such that the voltage difference at the input terminals of each comparator represents the voltage at the triac terminals with no added d.c. component. The outputs of comparators supply a square-wave voltage with zero-crossings synchronized perfectly with those of the main voltage at the terminals of the triac. The square-wave voltages are passed via compacitors and diodes to a comparator which reserves a string of negative pulses synchronized with zero-crossings of the triac. If the comparator is gated by an IN signal indicating that the temperature is above a predetermined value, the pulses are fed via the transistor of the gate of the triac to fire it.

Abstract: An apparatus is disclosed for activating a thermostat for an air conditioning or heating system. The apparatus comprises a control circuit and a controllable switch connected to activate and deactivate the thermostat controlling the air conditioning or heating system. A timing circuit provides a first timing period in which the thermostat is deactivated in addition to providing a second timing period to activate the thermostat. The control also includes a circuit for deactivating the thermostat for a period of time in the event the compressor terminates operation for any reason. An optional occupancy sensor increases the time of deactivation of the thermostat during periods of non-use of the area being air conditioned or heated. The foregoing abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter.

Abstract: A float operated switch (21) is actuated when the level of refrigerant fluid in a reservoir (11) is below a predetermined value to produce an electrical signal. The signal is delayed by 10 to 30 seconds and applied to a switch circuit (54) to disengage an electromagnetic clutch (63) and thereby de-energize a compressor (64). The clutch (63) is also disengaged by the action of a thermal switch (61) when the temperature in a space which is being air conditioned drops below a predetermined value. The operation of the float operated switch (21) is inhibited when the sensed temperature is below the predetermined value and also when a motor which drives the compressor (64) is not operating to prevent erroneous de-energization of the compressor (64).

Abstract: A control means is disclosed that is used with a closed refrigeration system having a chiller and a condenser to provide refrigeration to chill the fluid medium and a refrigerant pump for pumping the refrigerant through the system with refrigerant capacity control means determining the capacity of the refrigerant, the control means for the system using signal inputs representative of outside air temperature, return chilled water temperature, supply chilled water temperature, and condenser temperature, in which settable controllers are used to determine the optimum temperature signals for controlling the system at any given time. A timer is also connected to the control mechanism for alternately interrupting an optimum temperature signal to reduce the overall change in the control signal. Additional control may be obtained through the use of signals representative of humidity, strong solution temperature and cooling water output pressure.

Abstract: In a car-mounted air-conditioner driven by a mechanical power source provided on a car and capable of starting the operation for cooling or warming the air in the car room or cabin at a preset time under the control of a microcomputer, the microcomputer is interrupted at the preset time to be caused to compare the air temperature of the car room with a preset temperature and only when the air temperature is found to be outside a suitable temperature range, the microcomputer actuates the mechanical power source to start the operation of the air-conditioner.

Abstract: An automatic chiller control is disclosed for providing a temperature sensitive load limit compressor control on a cooling water system, such as is used in buildings for air conditioning. The controller operates across at least one motor driven compressor and operates to adjust the vane inlet to a typically centrifugal compressor. Control is provided in discrete steps responsive to changes in cooling water temperature as the water typically returns from a building. The control when operated in the automatic position starts the chiller at minimum possible power consumption. Increasing load or unload of the chiller is provided in incremental steps (for example 5% of full load) at preselected time intervals (for example 10 minutes) which are typically adjustable to any other desired time span. The control seeks the required motor power output without waste of power.

Abstract: A timing circuit is coupled to control operation of a chiller system in an air conditioner. The timing circuit includes an initial timer to limit to a minimum the amount of coolant initially admitted to an air conditioner compressor upon startup. This drastically lowers the initial amperage demand by the compressor. A chilled water return sensor monitors the temperature of water as it returns to thermal contact with the air conditioner coolant. The return sensor operates a duty cycle timer to intermittently load a line that serves to increase the supply of coolant to the air conditioner compressor. This lowers the average amperage demand of the air conditioning system.

Abstract: A control apparatus for an air conditioner, which selects the operation of the air conditioner between a first mode of warming a room and a second mode of cooling a room, the first mode having a defrosting pause period for defrosting the outdoor heat exchanger, the second mode having a restart-preventing pause period for preventing restarting of a compressor motor, and the abovementioned selection between two modes is made by controlling a logic circuit 16 constituted as a semiconductor IC by applying specified controlling signal thereto.

Abstract: In the main intended application of the arrangement according to the invention, that is, using a reversible motor compressor in a heat pump in a refrigerating or air conditioning system, it is desirable to insure a delay during reversal of the direction of compressor operation. A control arrangement is provided in which the control system controls the direction of motor operation or compressor capacity in accordance with temperature conditions, the system including control means for effecting operation in a low capacity direction or condition, or alternatively in a high capacity direction or condition in response to one set, and another set, respectively, of temperature conditions and with timer means delaying a restart of the compressor motor for at least a predetermined time in response to a condition of the control means operative to initiate a change in the operating direction or condition of the compressor when it restarts.

Abstract: Apparatus and method for storing material at and below a permissible upper temperature below the freezing point in a refrigeration chamber containing a heat exchanger and a thermostat to activate a refrigeration to supply coolant to the heat exchanger to maintain a set temperature. Periodically defrosting the heat exchanger by introducing heat, usually by an electric heating element in the refrigeration chamber, but prior to initiating defrosting, the thermostat is taken out of control of the refrigeration unit and the latter automatically activated to effect a drop in temperature in the chamber sufficient to prevent the stored material from exceeding it permissible upper temperature during subsequent defrosting.

Abstract: A slab-type ice maker apparatus wherein a slab of ice is formed on an inclined evaporator plate by the flowing of water over the upper surface of the refrigerated plate. A control is provided for sensing the temperature of the evaporator plate so as to determine when the thickness of the ice slab reaches a minimal preliminary thickness and continuing the ice slab formation for a preselected period of time subsequent to that determination to provide the completed final thickness slab. The thermally responsive sensing structure is mounted to the underside of the evaporator plate for improved sensing operation. The rate of flow of the water is reduced subsequent to the determination of the formation of the minimal thickness slab for improved efficiency in completing the formation of the final slab. Sensing structure is provided for determining the transfer of the ice slab to a slab dividing grid from the refrigerated plate.

Abstract: An energy conserving system is disclosed for heating and air conditioning multi-zone structures such as multi-story office buildings.A conventional heating and air conditioning system for a multi-story building has a central cooling unit for supplying chilled water for cooling and separately controlled fans or blowers for circulating cooled air in each story or zone. Separately controlled air heating (or reheating) means is provided for each story or zone. Usually the system is inactivated at night and on weekends in office buildings. When the system is inactivated, by-pass timers are provided to permit the system to be turned on in selected areas during off hours.An energy conserving system (and method of operation) for the aforementioned heating and air conditioning system includes timing means operated sequentially at different periods of time which shut down the coolers prior to shutting down the blowers at the end of the day.

Abstract: A switching system for controlling operation of conventional environmental apparatus of the type having an electrical connection adapted to be coupled with a supply of electrical current includes a switching circuit in a first housing for making and breaking a circuit connection between the connection and the current supplied, and a control circuit electrically coupling a magnetic detector with the switching circuit in order to operate the switching circuit to alternatively make and break the circuit connection between the power cord and the current supply responsive to detection of a magnetic element.

Abstract: In a refrigerator comprising a cabinet, means to refrigerate contents of a chamber within the cabinet, a door for access to such chamber, a fan to circulate air within such chamber, and a switch operable with the door to a first mode wherein the switch enables the fan when the door is closed and to a second mode wherein the switch disables the fan when the door is opened, a relay having contacts arranged to be closed after a delay of preset duration from energization of the relay and to be opened upon deenergization of the relay is connected so as to be energized in the second mode of said switch, so as to be deenergized in the first mode of the switch, and so as to enable the fan when the contacts are closed. A lamp indicates that the contacts are closed.

Abstract: A sensing device for use in a control for an alarm indicating an undesirable operating temperature condition within a refrigeration apparatus cabinet. The sensing device is mounted to have at least one surface thereof in thermal association with a liner portion of the refrigeration apparatus cabinet defining a refrigeration chamber therein. The sensing device is further responsive to the temperature of the refrigerated air within the chamber. The sensing device incorporates a time delay in responding to temperature changes within the refrigerated chamber to avoid false operation of the alarm. The device may be mounted in an insulating housing to provide a further time delay in the air temperature sensing functioning thereof.

Abstract: A thermally responsive sensor assembly such as for use in providing a warning signal indicating a sensed high temperature condition within a refrigeration apparatus. The sensor assembly includes a temperature detector embedded in a body of synthetic resin material. The detector is disposed within the resin body so as to provide an integrated sensing of the temperature condition existing outwardly of the body. The temperature condition is transmitted to the temperature detector within the body under the joint control of the surface heat transfer coefficient of the body, the thermal conductivity of the body material, and the heat capacity of the body. The resin material preferably has a substantially constant thermal diffusivity over the desired operating range of the sensor assembly. Further, the resin material may have a substantially constant low thermal conductivity over the desired temperature range. The resin material may be a styrenic resin material, such as high impact polystyrene.

Abstract: A startup and shutdown control for a cryogenic freezing tunnel for freezing food products in which the rate of flow of cryogen into the tunnel is normally regulated by a thermal regulator, including an auxiliary flow regulator for maintaining a predetermined flow of cryogen to the tunnel independently of the thermal regulator, a first startup interval device, comprising a counter responsive to movement of the tunnel conveyor, for actuating the auxiliary flow regulator to provide a constant flow of cryogen to the tunnel after a first startup interval measured from the initiation of movement of a supply of food products to the tunnel, and a second startup interval device, comprising a timer, to cut off the flow of cryogen via the auxiliary flow regulator after a second startup inverval.

Abstract: An automatic control apparatus for protecting the compressor motor used with the refrigeration system of an air conditioning unit. The control apparatus has a timer for prohibiting the restart of the compressor motor until the lapse of a predetermined time after temporary stoppage of the compressor motor, and a holding circuit for holding a power source voltage for a predetermined period of time while the operation of the air conditioning unit is stopped. Even if the power supply is turned off, therefore, the source voltage supplied by the holding circuit enables the timer circuit to continue its operation for a predetermined length of time.

Abstract: A minimum off-time protection arrangement is disclosed for compressors, particularly refrigeration type compressors. A current transformer is placed in the circuit which controls the switching of the compressor and that current transformer provides a control signal to a minimum off-time circuit. The minimum off-time circuit prevents the compressor from being restarted for some minimum period of time after once being operated.

Abstract: A control system for regulating operation of a heat pump includes a basic timer circuit which is utilized in different ways for different purposes. The system senses pressure across the outdoor coil, outdoor temperature, temperature in the liquid line to and from the outdoor coil, and temperature of the compressor discharge line. The control system initiates a defrost cycle for the outdoor coil responsive to a high static pressure across the outside coil, at the same time that the liquid line temperature is below a preset temperature. The defrost cycle is terminated when the liquid line temperature reaches a given temperature or when that liquid line temperature has been at a lower temperature for a certain time interval as determined by the basic timer circuit. When the compressor is shut down, the timer is also started to ensure that the compressor is not brought back on before the expiration of the basic shut-down time interval.

Abstract: An air conditioning system having a refrigerant system including a compressor, a condenser coil and fan, and an evaporator coil and fan and including a control system which comprises an electrically operated timer switch for alternately connecting the compressor for a preselected first period of time and disconnecting said compressor for a preselected second period of time, a thermostat for starting the timer when the sensed ambient temperature falls outside a preselected temperature range and for stopping and overriding the timer to disconnect the compressor from the terminals when the ambient temperature falls within the preselected temperature range. The evaporator fan continues to run after the compressor has been turned off thereby continuing to provide additional air cooling without the expenditure of energy to run the compressor.

Abstract: A control system for a central air conditioner. The air conditioner includes an outdoor condensing unit including a refrigerant compressor, an indoor evaporator unit, an indoor thermostat responsive to the indoor temperature for controlling the air conditioner, and a control system for protecting the air conditioner and indicating to the user certain malfunctions in the air conditioner should they occur. The malfunction indication may be by means of signal lights and a manually operable reset control is provided permitting the user to reset the control system. The malfunction indicator and reset control are disposed adjacent the thermostat for facilitated determination of the system operating condition. The control system includes an improved control portion for starting of the compressor motor which is arranged to prevent operation of the system in the event of a low power supply voltage condition.

Abstract: A control system for a central air conditioner. The air conditioner includes an outdoor condensing unit including a refrigerant compressor, an indoor evaporator unit, an indoor thermostat responsive to the indoor temperature for controlling the air conditioner, and a control system for protecting the air conditioner and indicating to the user certain malfunctions in the air conditioner should they occur. The malfunction indication may be by means of signal lights and a manually operable reset control is provided permitting the user to reset the control system. The malfunction indicator and reset control are disposed adjacent the thermostat for facilitated determination of the system operating condition. The control system includes an improved control portion for starting of the compressor motor which is arranged to prevent operation of the system in the event of a low power supply voltage condition.

Abstract: The heat pump system includes a first and a second centrifugal compressor arranged in series relation in a system including interstage expansion of the refrigerant. A pair of parallel circuits is provided for controlling the energization of the compressors in a sequence in which the first to start compressor must be energized to obtain completion of the second parallel circuit required for energization of the second to start compressor. The start of the second compressor is delayed for a period permitting the first compressor to come up to speed and the first circuit controlling the energization of the first compressor will be interrupted unless the second compressor has started within a short period of time after the time delay in starting the second compressor.

Abstract: A control circuit for a motor usable in a refrigeration system has a variety of condition sensors including means to sense a low refrigerant pressure and timing means to override the sensing of low refrigerant pressure for a time period during motor start-up. A lockout circuit prevents re-start of the motor following a fault condition.

Abstract: A fail-safe timing circuit energizable in response to a starting signal for activating a system, such as an air conditioning system, includes a first switching circuit responsive to the request signal to activate the system to commence its operation tentatively, a time-out circuit responsive to the starting signal for generating a time-out signal after a predetermined time delay interval, a circuit responsive to a system variable such as the compressor oil pressure achieving a given desired value, for preventing the time-out circuit from generating its time-out signal, and a second switching circuit for causing the first switching circuit to de-activate the system in response to the time-out signal. As a result, the system is prevented from operating in an undesirable or unwanted manner should the system variable not reach the predetermined condition within the timing interval.

Abstract: A control circuit for a motor has an electronic RC timing circuit with a fluid pressure switch for shunting the timing circuit if the fluid pressure reaches and maintains a predetermined magnitude. The timing circuit terminates the energization of the motor when not shunted for a predetermined duration.

Abstract: An automatic ice making machine having a control combining a timer with a thermostat to insure the attainment of desired temperatures in an ice forming enclosure and the retention of water in the ice forming enclosure for sufficient time to produce desired freezing at which time the control acts to automatically terminate the ice forming cycle and to initiate an ice harvesting cycle over recurring cycles of freezing and harvesting.

Abstract: The compressor motor of an air conditioning unit is operatively coupled to a A.C. line through a solid state electronic switch. Triggering signals for the switch are supplied from an oscillator circuit which is D.C. isolated from the switch, the trigger signals being coupled via transformer coupling. The oscillator is in turn thermostatically controlled in accordance with the cooling demand. The oscillator is also interlocked via a photocoupling device with an electronic timer circuit and with an undervoltage sensing circuit. The timer imposes a mandatory minimum delay between successive energizations of the compressor motor thereby permitting time for pressures in the refrigeration circuit to subside. The undervoltage sensing circuit is responsive to an electrical brownout condition for shutting down the motor should an electrical brownout condition occur. The undervoltage detector also contains a blackout detector section which shuts down the motor more rapidly during more extreme undervoltage conditions.

Abstract: A control system for a motor having a required oil pressure for the safe operation thereof, the system having a time delay switch for interconnecting an electrical source to the motor to operate the same each time the time delay switch is initially activated by being placed across the power source. The time delay switch has a time delay bimetal means that is adapted to move and open the switch if the oil pressure of the motor does not reach the required value within a predetermined time period from the initial activation of the time delay switch. An oil pressure responsive switch is operatively interconnected to the time delay bimetal means and to the motor to terminate the switch opening movement of the time delay bimetal means if the oil pressure reaches the predetermined value thereof during the predetermined time period so that the motor will be continuously operated as long as the system is not manually or automatically turned off or the oil pressure does not fall below the predetermined value thereof.