Thermo King 914 724, Manual

Page: 54 / 111

Electrical Maintenance (Rev. 1/99)
44
12 Volt System, Single Phase Electric Standby
The DC voltage should be 12 to 15 volts and the current
through the 2B wire should be less than 35 amps. If the cur-
rent is less than 35 amps and the voltage is less than 12
volts:
1. Check the AC line voltage and the transformer fuses.
The line voltage must be at least 90% of the voltage
specified for the unit. If the AC line voltage is accept-
able and the transformer fuses are intact, go to step 2.
2. Measure the transformer output voltage (AC) at the ter-
minal board. Measure the voltage between wires A and
B. If the transformer output voltage is less than 16 volts
AC, the transformer is defective. If the transformer out-
put voltage is acceptable, go to step 3.
3. Check the rectifier output voltage (DC) on the 2R wires
at CB1.
If the rectifier output voltage is less than 14 Vdc and
the load is not excessive (less than 35 amps), check the
choke coil jumper to make sure that it is installed cor-
rectly.
If the rectifier output voltage is more than 14 Vdc, the
load is not excessive (less than 35 amps), and the choke
coil jumper is installed correctly, the rectifier is defec-
tive.
If the rectifier output voltage is more than 14 Vdc, the
choke is defective.
24 Volt System, Single Phase Electric Standby
The DC voltage should be 24 to 30 volts and the current
through the 2B wire should be less than 22 amp. If the cur-
rent is less than 22 amps and the voltage is less than 24
volts:
1. Check the AC line voltage and the transformer fuses.
The line voltage must be at least 90% of the voltage
specified for the unit. If the AC line voltage is accept-
able and the transformer fuses are intact, go to step 2.
2. Measure the transformer output voltage (AC) at the ter-
minal board. Measure the voltage between wires A and
B. If the transformer output voltage is less than 32 Vac,
the transformer is defective. If the transformer output
voltage is acceptable, go to step 3.
3. Check the rectifier output voltage (DC) on the 2R wires
at CB1.
If the rectifier output voltage is less than 28 Vdc and
the load is not excessive (less than 22 amps), check the
choke coil jumper to make sure that it is installed
correctly.
If the rectifier output voltage is less than 28 Vdc, the
load is not excessive (less than 22 amps), and the choke
coil jumper is installed correctly, the rectifier is
defective.
If the rectifier output voltage is more than 28 Vdc, the
choke is defective.