Control System Notes
The following procedures must be followed when working on units equipped with
microprocessor based control systems.
• Never use testers consisting of a battery and a light bulb to test circuits on any
microprocessor based equipment.
• Before connecting or disconnecting the battery, the unit must be turned off.
• Any time a Return Air or Discharge Air sensor is replaced Service Procedure D01A
must be followed. If a graded sensor is replaced it must be calibrated as shown in
Service Procedure A15A.
• Any time the Microprocessor is replaced, these Service Procedures must be used:
A02A Recording Existing Microprocessor Setup
A03A Microprocessor Removal and Replacement
A04A Microprocessor Setup
• Any time the Interface Board is replaced, Service Procedure A03A must be followed.
• Any time welding is to be done on the unit or vehicle Service Procedure A26A must be
followed.
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