Two electricians were troubleshooting an HVAC (condenser) unit in a control room. Both employees went to the control room and applied group lockout to a single disconnect rated at 250 VDC power. After locking out the power to the control room and condenser unit, the employees began troubleshooting several deficiencies they observed while looking through the control panel. After repairing those items, the two employees removed the locks and validated that the repairs were working. The employees observed everything working as required except the HVAC compressor. The injured employee went up to the condenser area on an elevated walking surface that was covered in blaze which is a byproduct of the coke produced at the plant. The accumulation of blaze created an uneven surface. The employee had to remove an exterior covering or guard to validate that 250 VDC was coming from the thermostat to the junction box on the compressor motor. The employee squatted down and lost his balance before checking for 250 VDC. The employee reached to catch himself and in doing so grabbed the belts that drive the compressor motor. When contact was made, the motor began running and the employee's left hand was pulled through the pulleys amputating his left middle and ring fingers.