Danfoss Turbocor TT Series, Service Manual, Page: 29 / 294

9. Using an appropriately-rated voltmeter with the 1000VDC range selected, insert the positive voltmeter
lead into the DC (+F) test harness lead, and the negative voltmeter lead into the DC (-) test harness
lead. If the voltage corresponds toTable 1-2 Expected DC Bus Voltage, the DC bus voltage is correct and
HV DC (F1) fuse on the Soft Start is intact. This would imply that the Soft Start and Silicon-Controlled
Rectifiers (SCRs) are functioning correctly; proceed to Step 12. If voltage reads 0, go to Step 10.
Table 1-2 Expected DC Bus Voltage
Compressor Nameplate AC Voltage Acceptable AC Voltage Range Expected DC Bus Voltage Range
575 VAC 518-632 VAC 700-853 VDC
460 VAC 414-506 VAC 559-683 VDC
400 VAC 360-440 VAC 486-594 VDC
380 VAC 342-418 VAC 462-564 VDC
10. Leaving the DC(-) test lead in place, relocate the positive (+) test lead to DC(+). If DC voltage is
consistent with Table 1-2 Expected DC Bus Voltage, this would imply that the Soft Start and SCRs are
working correctly, but the HV DC fuse (F1) on the Soft Start is an open circuit, refer to Section 4.24 High
Voltage DC-DC Converter on page 204 to verify the DC-DC Converter.
11. If the DC voltage is not present or is not consistent with Table 1-2 Expected DC Bus Voltage, the
incoming AC voltage should be verified to be between the acceptable AC Voltage Range listed in Table
1-2 Expected DC Bus Voltage. Additionally the F2, F3, F4, F5, and F6 fuses need to be verified as well as
the SCR Diodes and SCR Gates. Refer to Section 4.18 Silicone-Controlled Rectifier on page 141 for
testing details.
12. For the Potted DC-DC, reset multimeter scaling to read 15VAC and connect to the 15VAC leads of the
DC Bus Test Harness. If the reading is zero, isolate the three-phase supply in accordance with Section
1.8 Electrical Isolation on page 22. When access is safe, remove the four (4) fasteners that hold the Soft
Start in position, and check fuses F2, F3, F4, F5, and F6 for continuity. If any fuse is found to be an open
circuit, replace it and return to Step 6.
13. If the 15VAC is not present for the Potted DC-DC, replace the Soft Start (refer to Section 4.14.3 Soft
Start Removal and Installation on page 117). If the 15VAC is correct, proceed to the next step.
14. When finished, remove the DC Bus Test Harness. Refer to Section 1.10.4 General DC Bus Test Harness
Removal on page 31.
• • • DANGER! • • •
The DC bus test harness is not designed to be left in the compressor during normal operation. When checks are complete, disconnect and
remove the test harness.
M-SV-001-EN Rev. H-1/23/2023 Page 29 of 294