ladder diagram schematic

[DANIEL909]

i was told in school to draw a ladder diagram schematic for a domestic refrigerator freezer combination..im guessing its a simple diagram showing defrost timer,heater, and motor im braking my head trying to figure this out can anyone help me out

[spimps]

http://en.wikipedia.org/wiki/Refrigeration

Decent starting point, you could add your freezer compartment and controls to the basic diagram.
Did they specify if the f/f had two compressors or one.At the moment there are several types ,simpleist is where the refigerant flows through the freezer compartment first then to the fridge compartment.Thermostat/control would be located in the fridge section so there is no actual exact control of the freezer,it keeps cold because the fridge thermostat will cycle on and as the refrigerant has to flow through the freezer first it stays cold too.
Frost free have a fan in the freezer and blow cold air up to the fridge through vents in the cabinet,this type would have a thermistor in the freezer to control temp via a pcb plus a motorised type flap to control cold air into fridge.
Lots of different types but tthose are a couple of basic ones.
Defrost heaters are controlled by a pcb too but did have a seperate defrost time which simply switched off power to the compressor/motor for around 20 minutes 4 times a day and gave power to a heater which was embedded within the evaporator,control was by thermostatic devices and also a overheat protector was in the circuit which would isolate power to the heater if there were any problems.

[nike123]

Ladder diagrams are used to describe the logic of electrical control systems.

http://www.seattlerobotics.org/Encoder/may97/ladder1.htm

Also it should be drawn to some standard and I recomend ISO
http://lhc-proj-qawg.web.cern.ch/lhc-proj-qawg/CD-ROM/Quality/QA403.pdf

Best way to do that is by some software which will keep you within standard so that anyone could understand your drawings.
http://www.control.com/thread/1026216941