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Heater Main Relay Test

  1. Remove heater main relay from relay block No. 2 in engine compartment. Check continuity between relay terminals. Continuity should exist between relay terminals No. 3 and 5, and between terminals No. 2 and 4. See Fig 1. Continuity should not exist between terminals No. 1 and 2.
  2. Apply positive battery voltage to terminal No. 5. Connect negative battery voltage to terminal No. 3. Continuity should exist between terminals No. 1 and 2. Continuity should not exist between terminals No. 2 and 4.
  3. If continuity is not as specified, replace heater main relay. If continuity is as specified, inspect heater fuse. Fuse is located in junction block No. 1, located beneath instrument panel. If fuse is okay, inspect wiring and connectors between A/C-heater control panel and battery. Repair as necessary. If fuse is blown, replace fuse and inspect for short circuit.
Fig 1: Identifying Heater Main Relay Terminals
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