Post by Gib Bogle
Sorry to belabour this issue.
One is the third from the left on the top row, the other is the first on the second row. The top one is $93, the other is $45. You can easily see that everything about them is the same except for the knob.
"Which one look like yours you need to buy that , that grey knob is there for a purpose ."
In fact mine is by a different manufacturer (Paragon not Invensys), is black not white, is otherwise identical as far as I can see. The knob is shaped like the one on the $93 timer, with the two cams.
Does the knob really have a purpose? It is clear that on my fridge it doesn't touch anything as it turns.
The knob just indicates the position in the defrost cycleLoading Image...
As for the pin numbering, the devices vary in the order they number
the pins. The pins have defined functions. If subbing, you have to
make sure you're connecting the wires to the pin function it belongs
with. These substitutes are not exact visual substitutes, but
"functional" substitutes. You, the installer, have to be aware
how to rewire the unit when installing it. If the original was 1234
and the sub is 4321, the wiring order would need to be reversed.
This is (obviously) a bitch, when the original timer has no numbers
at all on it :-/
"Basics of How a Defrost Timer Works
The defrost timer has four pins labeled from 1 to 4.
Each pin has its own function in the operation of the timer.
Pin 1: The main input power is attached to pin 1.
Pin 2: When in defrost mode, the power (pin 1) connects to pin 2,
which activates the defrost mode. Most defrost timers stay
in defrost mode for 30 minutes.
Pin 3: This is your ground / neutral wire. It will be separated
from the other three pins.
Pin 4: When the timer is not in defrost mode, the power (pin 1)
connects to pin 4, which activates the compressor and fan.
Most timers stay in this mode for 10 hours.
To test if the defrost mode is working, apply voltage to pin 1.
When the power supply is turned on, you should be able to measure
the voltage on pin 2.
Once the timer advances past 30 minutes, the compressor and fan
should turn on. You will know that the defrost timer is working
if you measure voltage on pin 4 when the timer is not in defrost mode.
The compressor and fan pin should be active for 10 hours (or however
long your defrost timer is designed to run). Once the 10 hours is over,
the defrost timer will switch back to pin 2, activating the defrost.
On mine, when the clockwork drive is in position and plastic gear mated,
I cannot move the indicator with my fingers. However, if the clockwork
drive is rotated out of position (I drilled out the two ally rivets), then
I can advance the indicator in the clockwise direction, and hear
"click-clunk". At the highest position on the indicator, the defrost
turns on. And 30 minutes later on the dial, it turns off. The cycle
repeats twice per whole indicator rotation. The whole knob rotation
is not a day - it is equal to two defrost intervals or 20 hours on mine.Loading Image...
The clockwork motor is 3 watts, and the gear reduction train is what
raises the torque to a high enough level to actuate the snap-action
cam. The switch must fall rapidly. The cam plastic must have a sharp
edge, or the switch contacts could be burned. It is because of
some of these design necessities that the torque level involved
is excessive, and you can hear some "hum" from the motor as it
struggles with its diminutive load.