Electrical Maintenance (Rev 1/99)
47
Defrost will not initiate automatically.
Use the following procedure to check the defrost initiation
timer. This procedure assumes the rest of the defrost system
functions properly.
1. Place jumper W2 in the fast clock position (see the
appropriate drawing).
2. Ground the 12 circuit.
3. Defrost should initiate in approximately 1 to 2 minutes.
4. If defrost does initiate on the timed defrost interval, the
timer is defective. The P.C. board should be replaced.
P.C. Board P/N 41-776 Test Procedure
1. Connect a 12 volt DC power supply, positive to GS1
stud hole (2 circuit) and negative to GS3 stud hole (CH
circuit).
2. Connect 12 volt positive to pin 1 of connector J6 (ACC
circuit).
3. Connect pin 3 and pin 5 of connector J4 together (this
connects 12 to CH).
4. Connect pin 1 of connector J2 and pin 1 of connector J4
together (this connects 7 to 7B).
5. Plug the cab box into the P.C. board with the cab box
harness.
6. Connect a variable resistance (620 to 1200 ohms) to the
two pin connector on the cab box harness (this simu-
lates the thermostat sensor).
7. Plug in the six relays as specified on the board.
8. Replace any fuses that are missing or blown.
9. With the power supply turned on and the cab box
turned off, PL3 only should light.
10. Turn cab box on and turn the setpoint to “00” degrees.
11. Turn the variable resistance until the cab box shows
“05” degrees.
12. LEDs PL1, 2, 3, 5, 8, and 11 should light as well as the
LED in the cab box display between the digits at the top
of the display and the snowflake LED.
13. Turn variable resistance until the cab box shows “00”
degrees.
14. All LEDs except PL3 should go off.
15. Turn the variable resistance until the cab box shows
“-05” degrees.
16. LEDs PL1, 2, 3, 5, and 9 should light as well as the
LED in the cab box display to the top left of the digits.
17. Jumper on W2 away from J1, and turn R16 fully
counter clockwise.
18. Turn the variable resistance until the cab box shows
“05” degrees.
19. In about 1 minute the circuit should go into the defrost
mode. In this mode LEDs PL3, 7, 8, and 11 should light
as well as the defrost indicator on Move the jumper on
W1 toward connector J1, the cab box.
20. In another minute and 15 seconds the circuit should
come out of the defrost mode. LEDs PL1, 2, 3, 5, 8, and
11 should light.
21. Turn cab box and power supply off.
22. Disconnect pin 1 of connector J6 from the positive side
of the power supply. Connect pin 4 (or 5) of connector
J5 and stud hole GS2 to positive.
23. Turn power supply and cab box on.
24. With cab box display showing “05” degrees LEDs P11,
2, 3, 5, 6, 8, and 10 should light as well as the power
cord indicator on the cab box.
25. When circuit goes into the defrost mode LEDs PL3, 6,
7, 8, and 10 should light.
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