8145-20 is 240Volt defrost timer:
You are testing the 8145-20 timer.
The timer dial should rotate continuously. Trippers on dial rotate around. When they reach the trip switch, the timer starts the defrost cycle.
Terminal 3 has power during defrost cycle.
Terminal 4 has no power during defrost cycle.
With 240Volt timer, terminals 1 and 2 and N and X test for live power to ground at all times.
The limit switch is connected to terminal X and to terminal N.
During the defrost cycle, the limit switch measures the pressure or temperature.
When pressure or temperature reaches the set point, the limit switch closes the circuit and this trips the solenoid inside timer. The solenoid turns off the timer relay, and the defrost cycle ends.
At this point the timer turns off the defrost, and sends power to the refrigeration.
Terminal 3 has no power during refrigeration cycle. (The opposite of defrost cycle).
Terminal 4 has power during refrigeration cycle.
Test these terminals for power to ground. One or the other should have power at all times, but not both.
If timer will not enter defrost cycle, make sure the X-3596 trippers are not worn down.
Disconnect the wire to terminal X and see if defrost cycle will start.
Test terminals 3 and 4 again and see if removing wire from X caused a change.
Add a comment for more help
Take a moment and rate answer for accuracy:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on timer or any do-it-yourself project.
Fixya is always less expensive than a service call.