TRUCK SERVICE MANUAL TM 5-4210-230-14&P-1 BODIES AND CABS 4. Remove plug from outlet opening of filter dehydrator. Remove  cap  or  tape  from  outlet  hose.    Lubricate threads with refrigerant oil and connect outlet hose to filter-dehydrator. IMPORTANT To   avoid   contamination,   do   not   uncover   filter-dehydrator openings longer than necessary to make connections. 5. Evacuate   and   charge   air   conditioning   system   as outlined under SERVICE OPERATIONS. HEATER CORE Removal: 1. Raise hood and fender assembly. 2. Drain engine cooling system. 3. Remove cover from right side of instrument panel. 4. Remove cover from heater/evaporator unit. 5. Loosen hose clamps at heater core. 6. Open blend air door. 7. Remove heater core mounting screws (Fig. 51). 8. Disconnect   hoses   from   heater   core   and   pull   core outward (toward rear of vehicle) to remove. 9. Remove gaskets from ends of heater core. 10. Inspect  hoses  and  gaskets  and  replace  if  damaged or deteriorated. Installation: 1. Position gaskets on ends of heater core. 2. Open blend air door. 3. Position   heater   core   into   housing.      Align   slot   in heater  core  frame  with  rivet  at  front  of  housing  and push heater core into position 4. Install heater core mounting screws. 5. Connect   hoses   to   heater   core   and   tighten   hose clamps. 6. Refill engine cooling system. Fig. 51  Heater Core Mounting Screws 7. Set  heater  (HTR)  control  lever  at  "HOT".  Operate engine.    Check  for  coolant  leaks  and  coolant  flow through heater core. 8. Install covers on heater/evaporator unit and instrument panel. 9. Lower hood and fender assembly. HIGH    SPEED    AND    LOW    PRESSURE    SWITCH RELAYS Relays   are   mounted   on   defroster   duct   and   are located in front of instrument panel and above blower motor. Removal: 1. Disconnect battery cable. 2. Remove cover from right side of instrument panel. 3. If relays are accessible, proceed to Step 4. If  relays  cannot  be  reached,  remove  radio/  ash  tray panel, as follows, to gain access to relays. a. Remove radio/ash tray panel mounting screws and pull panel outward. CTS-2731  Page 35 PRINTED IN UNITED STATES OF AMERICA