A/C - Poor System Performance: Overview
Issue: 212/13/96
80/01/96/US
SUBJECT:
PRIDE - HVAC Printed Circuit Board Check/Replace
MODEL:
Range Rover 4.0/4.6
AFFECTED VEHICLES:
LP SA302295 to TA344173
LH
LJ
LD
DETAIL
Some Range Rovers may experience poor operation of the heating and ventilation unit To overcome these concerns, Land Rover has introduced a new Heating and Air Conditioning Control logic. The new control software has been fitted on the assembly line and produces a safe VIN of TA344173. Any vehicle after this VIN will have the new control software fitted upon assembly.
A fix has been designed which involves the replacement of the PC board in the control unit. Use the following procedure to replace the PC board.
The diagnostic steps and repair procedures detailed on this bulletin were developed as an element of the Land Rover Way OPERATION PRIDE. This TIB provides a library location for PRIDE information within the Land Rover North America technical literature system.
ACTION REQUIRED
Upon customer complaint for the symptoms outlined, perform the specified repairs. Reference should also be made to bulletin 86/02/96/US (Exterior Temperature Reading Incorrect) prior to replacing the control panel.
PARTS INFORMATION
STC 3702K HVAC Circuit Board
LRNASTATK Anti-static Mat Kit
PROCEDURE
Perform the diagnostic procedures and repairs as outlined for the repair of HVAC control units.
WARRANTY:
Normal warranty procedures and policies apply.
COMP. CODE:
6Y1U
SRO:
80.10.02 - Time 0.35 hr.
Remove HVAC control and inspect
80.10.89.27 - Time 0.55 hr.
Remove HVAC control, inspect and replace circuit board
NOTE:
Times and operation descriptions are modification of PRIDE manual information.
SYMPTOMS:
Poor operation of the heating and ventilation unit can be categorized by the following symptoms:
Symptom 1:
Poor performance of heating and ventilation system in automatic mode. Specifically, insufficient responsiveness to achieve and maintain selected cabin temperature after start-up in hot ambient conditions.
Symptom 2:
Delay after start-up in hot ambient conditions before cooled air is supplied.
Symptom 3:
Inaccurate exterior-temperature readout, especially after hot soak.
To overcome these concerns Land Rover is introducing a new Heater and Air Conditioning Control Panel with the following changes to overcome the above symptoms:
Symptom 1:
More aggressive fan speed control and revised dynamic performance strategy (including improved recirculation logic) to provide optimum performance in achieving and maintaining selected cabin temperature.
Symptom 2:
Logic changes within the unit eliminate the delay.
Symptom 3:
High temperature accuracy is improved due to changes made in the recirculation within the unit.
NOTE:
For more information on system characteristics, how the system works and diagnostics, see the HVAC specification document published with Operation PRIDE.
Refer to the Workshop Manual section 80, HVAC Controls, for removal instructions.
(Refer to this bulletin for the PC board replacement instructions)