Electrical Maintenance (Rev 1/99)
44
Troubleshooting the V250 Defrost System
with P.C. Boards P/N 41-1619 and P/N 41-
1812
Unit will not defrost when the manual defrost
switch is pressed.
A. Check the defrost termination switch.
1. The defrost termination switch should be closed at
temperatures below 42 F. Make sure the evaporator
temperature is below 42 F.
2. Disconnect the 12 wire from the defrost termina-
tion switch and place a jumper between the 12 wire
and ground. Press the manual defrost switch.
a. If the unit goes into defrost, the defrost termi-
nation switch is probably defective and should
be replaced. (NOTE: If this step is being per-
formed as instructed by later steps in this pro-
cedure, the defrost termination switch may not
be defective.)
b. If the unit does not defrost, go to the next step.
3. Check for voltage between P4-5 (12 circuit) and
P4-2 (CH circuit) at the P.C. board while pressing
the manual defrost switch (to energize the 11 cir-
cuit).
a. If voltage (approximately 12 volts) is present,
check the 12 wire from the P.C. board to the
defrost termination switch for an open or short
circuit and repair it.
b. If no voltage is present, remove the jumper
from the 12 wire at the defrost termination
switch and repeat step A.3.
If voltage is now present, repeat step A.2.
If voltage is still not present, go to the next
step.
B. Check the P.C. Board.
1. Check defrost fuse F5 (1 amp).
a. If fuse F5 is burnt out, replace it and perform
step A.2.
b. If fuse F5 is not burnt out, go to the next step.
2. If no voltage is present between P4-5 (12 circuit)
and P4-2 (CH circuit) with the 12 wire discon-
nected and the 11 circuit energized, check the fol-
lowing:
a. Remove the defrost relay from its socket.
Check for voltage on the 11 circuit at the 85
pin of the defrost relay socket while the press-
ing the manual defrost switch.
b. If no voltage is present on the 11 circuit, go to
step B.4.
c. If voltage is present on the 11 circuit, install a
new relay in the defrost relay socket. Recheck
the voltage on the 12 circuit while pressing the
manual defrost switch.
If voltage is still not present on the 12 circuit,
the P.C. board is probably defective and
should be replaced.
If voltage is now present on the 12 circuit, go
to the next step.
3. If voltage is present between P4-5 (12 circuit) and
P4-2 (CH circuit) with the 12 wire disconnected
from the defrost termination switch and the 11 cir-
cuit energized, check the following:
a. Ground the 12 circuit and press the manual
defrost switch.
b. The unit should go into defrost and the defrost
relay LED (PL7) should light. The defrost
relay was defective.
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