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1978-79 Models

  1. Attach a hand-held vacuum pump to vacuum amplifier side of thermal switch. Attach a vacuum gauge to EGR valve side of switch. With switch cold, apply vacuum to switch. No vacuum should be noted on vacuum gauge. If vacuum passes when switch is cold, replace switch.
  2. Bring engine to normal operating temperature to warm up switch. Apply vacuum to switch. Vacuum should be noted on vacuum gauge. If vacuum does not register on gauge, switch is stuck closed and must be replaced.
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