Trouble Compressor will not run (Cont’d) Possible Cause 4.   Fuses   blown. 5. Over-load  relays  tripped. Corrective Measure 4. Test fuses and renew if necessary. 5. Re-set relays and find cause of overload. 6.   Low   voltage. 6. Check voltage (should be within 10  percent  of  nameplate  rating). 7. Electrical motor in trouble. 7. Repair or replace motor. 8. Trouble in starting switch or 8.  Close  switch  manually  to  test control  circuit. power supply. If OK, check control circuit  including  temperature  and pressure controls. 9. Compressor motor stopped by oil 9. Check oil level in pressure differential switch. crankcase.  Check  oil  pump pressure. Sudden loss of oil from crankcase. Capacity  reduction  system falls  to  unload  cylinders. Liquid refrigerant slugging back to Adjust or replace expansion valve. compressor crank case. Hand operating stem of capacity Set hand operating stem to automatic control valve not turned to automatic position. position. Compressor continues to Pressure regulating valve not opening. Adjust or repair pressure regulating operate at full or partial load. valve. Capacity reduction system Broken or leaking oil tube between Repair leak. fails to load cylinders. pump and power element. Compressor continues to Pressure regulating valve not closing. Adjust or repair pressure regulating operate  unloaded. valve. Figure 5-9.—Trouble diagnosis chart-Continued. possible  causes  and  corrective  measures.  Figure  5-10 also lists some of the problems, causes, and corrective measures  and  includes  recommended  test  procedures that may be used to isolate the problems. SAFETY  PRECAUTIONS  USED  WHEN HANDLING  REFRIGERANTS The following safety precautions are the minimum required when you are using refrigerants: 1. Two people must be present at all times while refrigerant is being charged into a refrigeration system. NEVER leave the area unattended while charging is in progress. 2. Ensure that ventilation in the space is adequate to  keep  the  concentration  of  refrigerant  below  1,000 parts per million. If necessary, use portable blowers. 3.  If  refrigerant  is  being  charged  into  or  being removed  from  a  system,  prohibit  all  nonessential 5-15