Electronic A/C System - Added Self-Diagnostic Features
Number: 93-83-1ASection: 1A
Date: JAN. 1993
Corporate Bulletin No.: 241201
ASE No.: A7
Subject:
TRUCK ELECTRONIC AIR CONDITIONING SYSTEM INFORMATION
Model and Year:
1991-93 C/K TRUCKS
For the 1991 model year, self-diagnostic features were added to the Electronic Air Conditioning (EAC) system which are used in C/K trucks. These features are also used in 1992-93 model year vehicles.
In these systems, the control head communicates its diagnostic message to the service technician by flashing the various symbols located on the display panel.
It is important for the technician to recognize that these flashing displays represent a DIAGNOSTIC MESSAGE, and ARE NOT A RESULT OF CONTROL HEAD FAILURE.
NOTE:
When the technician is attempting to distinguish between normal diagnostic messages and a failed EAC control head, he should remember that all 1991-93 model year control heads utilize self-diagnostic features. However, 1988-89 model year product does not employ these features, even though these have an external appearance which is nearly identical to that of the later versions.
SELF-DIAGNOSTIC MESSAGES:
The control head will diagnose faults in the mode door motor, the temperature control door motor, and the A/C compressor system. When a fault is detected, the control head will flash the appropriate symbol on the display panel to notify the customer and/or technician of the problem. This flashing will last for two minutes following the failure occurrence. It will then stop to avoid distracting the driver. However, when the vehicle is restarted (ignition recycled), if the failure was present when the ignition was last ON, the display panel will again flash its diagnostic message for two minutes. This serves to remind the customer that the EAC system still has a fault and should be taken to the dealer for service. The diagnostic message will also reappear whenever the driver presses a function switch which would cause the faulty circuit to operate. In this case, as in the others, the display will flash for two minutes.
In summary, the control head will communicate a diagnostic message at following times:
1 WHEN THE FAULT IS FIRST DETECTED.
2 WHEN AN AFFECTED FUNCTION SWITCH IS PRESSED.
-- If a fault is present in the mode motor, pressing a mode function switch will cause the mode symbols to flash.
-- If a fault is present in the temp motor, pressing a temp function switch will cause the temperature cursors to flash.
3 WHEN THE IGNITION KEY IS RECYCLED (after engine start).
* All of the above messages will flash for two minutes.
REQUIREMENTS FOR SETTING/CLEARING FAULT CONDITIONS:
The chart outlines the three different diagnostic messages that the EAC control head may communicate. Letter codes are used in the FAULT, DEFAULT ACTION, and REQUIREMENT TO CLEAR columns. The meaning of each letter code is described in the list appearing in the chart.