TM   9-2320-363-34-1 TROUBLESHOOTING  AND  TESTING  THE  AIR CONDITIONING   SYSTEM (All Except M915A2 and M916A1) Preliminarv   Checks cool   spots   exist,   replace   the   receiver-drier. Before  testing  the  operation  of  the  air  conditioning system,   make   the   following   checks: 1. 2. 3. 4. 5. Make   sure   the   refrigerant   compressor’s drive   belt   is   not   damaged   and   is   correctly tensioned.   Also   check   the   compressor mountings   for   tightness. Check  for  broken,  burst,  or  cut  hoses;  also check  for  loose  fittings  on  all  parts. Check   for   road   debris   build-up   on   the condenser  coil  fins.  Using  air  pressure  and a  whiskbroom  or  a  soapy  spray  of  water, carefully  clean  off  the  condenser;  be  careful not  to  bend  the  fins. Check   the   color   of   the   moisture   indicator sight glass. If the color is a deep cobalt blue, the  refrigerant  charge  is  dry.  If  the  indicator is  not  blue,  the  system  is  contaminated  with moisture;   recover   the   refrigerant,   evacuate the   system,   replace   the   receiver-drier,   and add  a  full  refrigerant  charge. If  there  is  not  enough  airflow,  make  sure  that leaves   or   other   debris   has   not   entered   the fresh  air  ports  under  the  windshield.  If  debris has   entered,   it   could   clog   the   fins   of   the evaporator   core,   and   block   airflow. Also,  be  sure  that  all  ducts  are  connected  to the   dash   louvers   and   that   the   air-control flaps   in   the   heater   housing   are   moving properly   (this   requires   removal   of   the   right and  center  dash  panel). Performance  Tests Following  is  a  brief  description  of  symptoms  or conditions   that   could   exist   if   something   goes wrong  with  a  refrigerant  part. RECEIVER-DRIER The   receiver-drier   is   normally   at   outside temperature.  To  the  touch,  the  entire  length  of  the unit  should  be  the  same  temperature.  If  noticeable A  blockage  at  the  inlet  of  the  unit  will  cause  high head   pressures;   outlet   blockages   will   cause   low head  pressures  and  little  or  no  cooling. If  the  moisture  indicator  is  pink  or  white  (showing that  the  system  is  wet),  the  receiver-drier  is saturated  with  moisture  and  must  be  replaced. C O O L I N G    S Y S T E M Although  they  are  not  physically  connected,  there is   a   close   tie   between   a   vehicle’s   air   conditioner and   its   cooling   system.   Poor   air   conditioner cooling   can   be   the   result   of   a   problem   in   the cooling   system. If  the  cooling  system  does  not  work  correctly,  the heat  of  the  engine  will  rise  to  abnormal  levels.  The added   heat   will   transfer   to   the   air   conditioner, other  underhood  parts,  and  maybe  make  its  way into  the  cab.  The  added  heat  makes  it  necessary for  the  air  conditioner  to  work  harder  and  at  the same   time,   it   reduces   the   air   conditioner’s   ability to  cool  down  the  air  in  the  cab.  Also,  if  the  water regulating  valve  isn’t  closing  all  the  way,  heat  will enter   the   cab,   giving   the   impression   that   the   air conditioning   system   is   not   working. Refer  to  the  engine  cooling  section  for  cooling system   troubleshooting. EXPANSION  VALVE Problems   that   start   in   the   expansion   valve   show up  as  follows:  when  stuck  closed,  the  evaporator coil   and   the   expansion   valve   will   be   at   outside temperature;  when  stuck  open,  both  the  coil  and the   valve   will   be   extremely   cold   with   frost   or   ice build-up. Because  the  expansion  valve  channels  are  very small,  blockages  in  the  system  tend  to  be  found here  (the  valve  is  very  sensitive  to  contamination). Usually,   the   contaminant   is   water;   less   than   a drop  of  water  is  all  it  takes  to  make  the  valve inoperative.  When  water  reaches  the  valve,  the extreme  cold  that  results  from  the  pressure  drop freezes   the   water,   forming   a   block   of   ice   in   the valve.  After  the  system  shuts  down  and  the  valve warms  up,  the  ice  melts,  and  the  valve  operates again,  only  to  freeze  up  when  moisture  returns. Change  1 2-28.1