TRUCK SERVICE MANUAL TM 5-4210-230-14&P-1 BODIES AND CABS COMPONENT PROBLEM ANALYSIS COMPRESSOR Some possible failings of the compressor include: 1. Leaking    Front    Seal    This    allows    refrigerant    and lubricating   oil   to   escape   from   system   in   loss   of cooling and damage to compressor. 2. Bearing  Failure  Usually  the  result  of  material  wear but  can  result  from  excessive  drive  belt  tension  or pulley misalignment. 3. Burned-Up Compressor Caused by lack of lubricating oil.    This  emphasizes  the  need  for  checking  the  oil level in the compressor at the time of system service. In the event that compressor failure is severe enough to form metal particles, purge compressor discharge- to-filter-dehydrator    lines    with    4.5    kg    (1    lb.)    of refrigerant and replace the filter-dehydrator. For  compressor  service  procedures,  refer  to  Bodies and  Cabs,  Section  CTS-2577  of  the  Truck  Service Manual MAGNETIC CLUTCH The two most common clutch failures are: 1. Burned-Out Facings. 2. Broken Torque Springs. Both   of   these   failings   are   usually   symptomatic   of troubles    somewhere    else    in    the    system.    (Example:    A restriction    in    the    condenser    will    cause    excessive    head pressures,  which  in  turn  will  overwork  the  compressor  and clutch, eventually causing failure of one or both.) For  clutch  service  procedures,  refer  to  Bodies  and Cabs, Section CTS-2577 of the Truck Service Manual. THERMOSTATIC TEMPERATURE CONTROL SWITCH The    thermostatic    temperature    control    switch    is relatively   trouble   free;   however,   should   it   fail,   it   must   be replaced.    If  the  clutch  remains  engaged  continually,  check the  sensing  tube  of  the  control  switch  to  see  that  it  has  not been  pulled  out  of  the  evaporator  core.    The  sensing  tube should  be  located  in  the  evaporator  core  as  shown  in  Figure 59. Also,  make  sure  air  conditioning  (A/C)  control  cable is properly adjusted. CONDENSER Possible problems with the condenser include: 1. A leak in the condenser. 2. A  stoppage  or  restriction  of  refrigerant  flow  through the condenser.  This could result from some foreign material inside the core or by a sharp bend or dent in the condenser tubing or in the hoses leading into or out of the condenser. (Make   a   visual   check   to   make   sure   this   has   not occurred.) 3. A restriction of air flow through the condenser.  This is  the  most  common  problem  and  results  from  dirt, leaves, etc.  collecting on the front area. A stoppage or restriction of refrigerant flow or air flow through  the  condenser  will  be  indicated  by  a  high discharge pressure reading on the test gauge. Restriction of refrigerant flow will show a lower than normal suction pressure on the test gauge. Restricted   air   flow   will   build   high   discharge   and suction pressures. In  some  instances  tubing  may  be  replaced  or  leaks may   be   repaired   by   silver   soldering   if   the   spot   is accessible,    however,    a    stopped-up    or    internally restricted core must be replaced. CAUTION Never weld, solder, steam clean or use any excessive amount of  heat  on  any  of  the  refrigerant  lines  or  components  of  the refrigeration   system   while   the   system   is   charged.      Heat applied to any part would cause-the pressure of the refrigerant within the closed system to become excessive. EXPANSION VALVE Possible problems at the expansion valve include: 1. Stoppage - Stoppage in the system tends to occur at the valve or at the filter-dehydrator tank. 2. Valve   Sticking   -   The   valve   tends   to   stick   closed cutting  off  the  refrigerant  supply  to  the  evaporator and stopping all cooling from the air conditioner.