6-4.  Repairing  Refrigerant  Leaks a.  Locate  leak  (para  4-64). b. Discharge system (para 6-3), repair leak, and recharge  system  (para  6-3). Note. If soldering is necessary on any part of the system, a constant purge of dry nitrogen must be fed through the system being soldered to prevent scale formation within the system. 6-5.  Compressor  Motor  Burnout  Clean  Up Procedures a.  General.  Experience   has   demonstrated   that after a hermetic motor burnout, the system must be cleaned   thoroughly   to   remove   all   contaminants, otherwise,  a  repeat  burnout  will  occur. b.  Clean  Up  Procedures.  A  motor  that  fails  to start  may  be  due  to  improper  voltage,  a  malfunc- tion of the compressor start relay, or a compressor mechanical fault. Make certain that a burnout has occured  by  doing  the  following: (1) Check for proper voltage by turning off the main disconnect switch so that all power is off. (2)  Remove  the  front  access  cover. (3)  Remove  the  compressor  leads  at  the compressor  side  of  the  start  relay. (4) Close the disconnect switch to energize the control  circuit. (5)  Check  for  voltage  on  all  lines  at  both  the line  and  load  side  of  the  compressor  start  relay. Note. Before  checking  the  compressor  motor,  make sure the compressor is cool to the touch. Otherwise, a false indication may be obtained due to internal motor protectors being open. (6)  Check  the  compressor  motor  to  see  if  it  is electrically grounded or open. A 500 volt megger or an  ohmmeter  can  be  used  for  making  the  test. Typical  megger  reading  is  5  megohms. (7)  Purge  a  small  amount  of  refrigerant  gas from  the  compressor  and  smell  it  cautiously.  A motor   burnout   is   ususally   indicated   by   the customary  burned  odor. c.  Safety  Measures.  In  addition  to  the  electrical hazards,  the  serviceman  should  be  aware  of  acid burns.  Take  the  following  precautions: (1)   When   testing   for   odor,   release   a   small amount  of  gas  and  smell  it  cautiously  to  avoid inhalation  of  toxic  decomposed  products. (2) When discharging gas or liquid refrigerant from a burnout, avoid eye or skin contact with the product.  If  the  entire  charge  is  to  be  removed,  it should be discharged outside any enclosure. Do not discharge  into  an  open  flame. (3) When necessary to come in contact with oil or  sludge  from  a  burned  out  compressor,  rubber gloves  should  be  worn  to  avoid  acid  burns. d. Determine Severity of Burnout.  It is helpful to classify  burnouts  as  “mild”  or  “severe”  and  to  use the severity as a guide for the clean up procedure to be followed. The severity can be determined by the following means:  if possible, obtain a small sample of oil from the burned out compressor and analyze it,  using  an  acid  test  kit.  Discoloration  of  the  oil may  indicate  a  severe  burnout. e.  Clean  Up  after  a  Mild  Burnout.  When  the burnout  is  mild,  the  contaminant  can  be  removed by changing the liquid line dehydrator, or installing one, if the system did not have one originally. The procedure  to  follow  is: (1)  Discharge  the  refrigerant  system  (para  6- 3). (2)  Remove  the  burned  out  compressor  (para 5-17). (3)  Install  a  new  compressor  motor  (para  5- 17). (4)  Remove  the  dehydrator  and  install  an oversize  replacement  dehydrator. (5)  Pump  the  system  down  to  less  than  500 merons.  Break  the  vacuum  at  least  three  times  with a  small  refrigerant  charge,  bringing  the  suction pressure  up  to  approximately  3  psig. (6) Recharge the system and put in operation (fig.   6-2). f.  Clean  Up  after  a  Severe  Burnout.  Complete cleaning  of  the  system  is  required  as  follows: (1)  Discharge  the  refrigerant  system  (para  6- 3). (2)  Install  a  dehydrator  in  the  suction  line. Change  strainer,  as  well  as  changing  or  installing an oversize liquid line dehydrator. In this way, the suction   dehydrator   protects   the   new   compressor from  any  contaminants  that  may  remain  in  the system.  Leaving  a  permanent  type  dehydrator  in the suction line allows the serviceman to complete the clean up at one time. A pressure tap should be installed upstream of the suction dehydrator so that the pressure drop, from the tap to the service valve, can be checked after several hours of operation. A pressure  drop  in  excess  of  3  psig  is  generally considered  excessive. (3)  Check  the  expansion  device  and  clean  or replace  it.  Replace  sight  glass. (4)  Remove  the  burned  out  compressor  and install  the  replacement. (5)  Evacuate  the  system. (6) Recharge the system and put in operation. (7)  Check  pressure  drop  across  the  suction dehydrator  after  one  hour  of  operation.  Change,  if necessary,  and  evacuate  system. (8)  After  8  to  24  hours  of  operation,  change suction  dehydrator.  Check  odor  and  color  of  oil. Evacuate  system. (9) After 14 days of operation, check color and acidity  of  oil.  If  required,  change  dehydrators. Before clean up is completed, it is essential that oil is  clean  and  no  acid  is  present. 6-6