GB1515853A - Road vehicles having rear window demisters - Google Patents

Abstract

1515853 Control systems for vehicle window demisters LUCAS ELECTRICAL Ltd 13 May 1975 [17 May 1974] 22107/74 Heading H2H The rear window demister of a road vehicle is controlled so as to be de-energized automatically when the engine coolant reaches a predetermined value. A demister 16 of a road vehicle is energized by closing an ignition switch 12 and moving a switch 38 to its first operative position 39 whereupon, with a cold engine coolant the potential at the junction of the coolant sensor 23 and gauge 22 is such that transistors 31, 33 are off and transistors 46, 59 are turned on, the turning on of transistor 59 causing energization of relay 18 to close contact 15. When the engine coolant temperature reaches a predetermined value the potential at the junction between the sensor 23 and gauge 22 is such that transistor 31 turns on thus turning on transistor 33 which latches on transistor 31. Transistors 46, 59, now turn off to de-energize relay 18, opening contact 15 to de-energize the demister 16. With the circuit in this condition the de-mister will remain de-energized whatever the water temperature. If at any time when the demister is de-energized, movement of the switch 38 to its second operative position 41-position 39 remaining energized-a transistor 56 turns on and hence transistor 59 thus again energizing the demister 16 whereupon the demister can only be de-energized by opening the ignition switch 12. The circuit cannot be latched during a warm-up period by virtue of a diode 54.