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The machine uses semi-automatic defrost mode , the defrost control circuit as shown in the drawing , when the freezer frost layer thickness of about 10 mm , you can manually defrost manually trigger control so that wrapped around the freezing chamber evaporator electric wire heating defrost . When the temperature rises to 8.5 ¡æ automatically cut off the power supply wire heating and refrigeration compressor starts . To control relay RY02 , RY02 pulls in its normally open contacts connected 160Ω power defrost heating wire . When RY02 release , defrost heating wire heating power is turned off to stop while turning anti- freeze heating wires ( two 5KΩ heating wire in parallel ) power , and therefore anti- freeze and defrost heating wire can only work alternately .pyAservice manual download site
1 , circuit analysis : 14V DC power supply circuit output voltage of RY02 power while limiting by R812, D808 regulator , the C808 filter, the control circuit provides 6.8V operating voltage. Four voltage comparator Q802 (TA75339P) of a voltage comparator for defrosting temperature detection ; RY2 is a negative temperature coefficient thermistor , mounted on the defrost the freezer compartment is used to detect temperature ; two four-input NAND gate Q801 (TC4011BP ) is composed of two NAND gate RS flip-flop and defrost start button S101, R119, defrost stop button S102, R120 ~ R124 and defrost indicator light-emitting tube LED01, current limiting resistor R118 etc. defrost control circuit.
2 , defrosting
Press the defrost button S101, RS flip-flop 13 feet is pulled low. If the freezer temperature is very low at this time , RT2 greater resistance , and R810 for the 6.8V power supply voltage divider , the comparator inverting input voltage is less than 8 feet with the R808, R809 partial pressure set -inverting input pin 9 Basis 4.4V reference voltage , the comparator output 14 feet high, so RS flip-flop 11 feet high on output stability , Q812 is turned on , Y02 pull, cut anti- freeze heater power , so too the defrost heating electric heating start defrosting ( if the freezer temperature is not very low , even by mistake defrost button S101, it will not start defrosting ) ; with the freezer temperature rising , RT2 resistance smaller. When the temperature reaches 8.5 ¡æ, 8-pin voltage comparator voltage of more than 9 feet , 14 feet of its output goes low jump . Since this time has been reset disconnected S101 , RS flip-flop 13 pin input is high, so the output will jump 11 feet into a stable low level , Q812 deadline , RY02 release , defrost heater power to stop working, anti- freeze heater is energized work ; If the defrosting process by pressing the stop button S102, the RS flip-flop 9 foot jump goes low , the 11 -pin output goes low jump , Q812 deadline , so defrost sooner; Further, defrosting proceeds to late , with the inside temperature rises, the temperature control circuit may send a signal to start the operation of the compressor , but the start signal D803 bypassed to ground through Q812 , the defrost compressor will not be activated.
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