In residential units, timers are usually located behind the toe plate (front grille at the bottom of the unit) near the front or back of the unit, or sometimes next to the cold control (thermostat) inside the refrigerator compartment behind the control panel, and sometimes in the back of the unit. Pay particular attention to figures 11a-11e and 54c-54l. Different manufacturers use different timers with different terminals to energize the compressor and the defrost timer. This test assumes that terminal 4 is the defrost and terminal 2 is for the compressor. Before running a test, check the terminals on any particular unit being tested.
1. Disconnect the power supply.
2. Disconnect the timer.
3. Disconnect the block from the defrost timer by pulling it apart.
4. Disconnect the green ground wire, and disconnect the individual wires from the timer if there is no connecting block. Be sure to mark every wire so it may be reconnected correctly. (Method: make a little “flag” for each wire with masking tape and a fine line marker.)
5. Set the ohmmeter to the RX1 scale and zero it.
6. Connect the ohmmeter probes to the timer terminals 1 and 4; then using a screwdriver, coin, or putty knife blade, turn the cam on the timer clockwise very slowly. The meter should register a zero reading until a click is heard. At that precise moment, stop; the meter should register an open-circuit reading. If not, the timer should be replaced.
7. Place the two ohmmeter probes on terminals 1 and 2 and continue turning the cam. A zero reading should be registered on the meter until a click is heard. Stop. The meter should register an open-circuit reading.
If not, the timer should be replaced.
8. Set the ohmmeter on the RX1000 scale and zero it.
9. Connect the ohmmeter probes to the timer terminals 1 and 3. The meter should register a continuity reading. Otherwise, the timer motor is bad and the timer must be replaced.
This test can determine if the timer has any electrical defects. Timers can also develop mechanical problems. Occasionally, a defrost timer motor freezes in one particular cycle, and it no longer advances because of mechanical problems (or a short or a disconnection in the timer motor).
To test the timer for mechanical problems, turn the cam very slowly clockwise. If you feel any “snag” anywhere while turning it, the timer should be replaced.
While the timer is disconnected from its electrical wires, visually check all of the terminals for burns. If there are any brown spots or burns on any of the terminals, replace the timer. When connecting the timer terminals to the system, make sure every connection is secure. Tighten loose connections and replace broken or frayed wires.
CHECKING THE TIMER MOTOR BY DIRECT CONNECTION
This test can determine if the timer motor has any electrical defects such as a short or a disconnection in the timer motor causing it not to advance. (Occasionally, a timer motor freezes in one particular cycle and no longer advances because of a mechanical defect).
1. Disconnect the power supply.
2. Turn the timer shaft to a point just before a click is heard and leave it there.
3. Using a test cord with insulated alligator clips, connect timer terminals 1 and 3 directly to the power supply (where the unit is normally connected).
4. If the timer motor starts turning, it is good. Otherwise, disconnect it from the power and replace the timer. (In some timers, you cannot see the motor rotation through its housing. In which case, wait for about fifteen minutes; if you hear the click, the timer is good. Otherwise, replace it).