I need a small circuit that can disconnect AC power (means will have a relay) when it detects freezing on coil. I have a non working appliance that I want to power up but also include a antifreeze circuit design so that when it senses ice or freezing on the coils it powers off/disconnects. can anyone help ? is there any such circuits available that can do this job ?
http://www .google.com/search?q=temperature.controller&num=100 Set it to limit at 33F.
Some form of direct frost detector perhaps. Polish a section of the coil to a mirror finish, and then use an optical reflectance sensor to detect frost formation.
Eric
Thermistor + comparator + relay D from BC
-- The OP wants to sense freezing, not dew point. http://www.google.com/search?hl=en&q=chilled+mirror+psychrometer&btnG=Search
--- View in Courier:
+12V>-----+-------+---------+--------+----+-----+ | | | | | | | | | [10k] |K | O------C [47k] [30k] | | [CR1] [COIL]- - -| | | +---|--[1M]--+ | | O--> |------+--+-----G 2N7000 [RTH] | [10k] | | | | | | | +---|-/ U1B [0.1µF]|[0.1µF]| | | | | | | | | | | | | GND>--+---+---+---+-----+---+-----------+-------+RTH is a thermistor with a resistance of 10K at 0C.
-- JF
No need to reinvent the wheel.
Those may not work very well with the +/-5oF tolerance on setpoint, not too mention no standard part number is suitable.
There may be but they will be junk. The best way is to modify the "sealed system" by including an evaporator pressure regulator set for a refrigerant saturation pressure corresponding to 33oF. You will need to know how to pump the system down, make proper flare connections, install pressure access ports and other fittings, and read something called a pressure gauge and something called a thermometer. Something like this:
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