Circuit Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The HVAC control module has an AUTO mode algorithm that is designed to detect a failure with the blower system or a failure with the A/C system. The HVAC control module, when in AUTO mode, requests the engine ON when continuous operation of the A/C compressor (not interrupted by the engine shutting off during stops) is required to cool the cabin in warm or hot weather. The failure detection algorithm monitors duct temperatures while the engine is requested ON under such conditions. If the algorithm does not see duct temperatures become cooler than 120 counts within 30 minutes of requesting the engine on for A/C operation the B013A will set and the HVAC control module will not request engine ON for A/C in warm or hot weather until the B013A is cleared.

The failure detection algorithm will activate if the following conditions are present:

The HVAC module is in AUTO mode.
The Outside air temperature sensor is in normal operating range.
The Inside air temperature sensor is in normal operating range.
The Sunload sensor is in normal operating range.
The Duct temperature sensors are in normal operating range and are reading warmer than 120 counts (warmer temperatures correspond to lower A/D count values).
A temperature setting that requires A/C operation under the current ambient conditions must be selected on the HVAC module.

Algorithm is a word that describes one of the many functions of the software inside the module. The algorithm looks at specific information that the HVAC module receives and based off that information the algorithm outputs specific functions. There is no single circuit or component that performs these functions; it is a combination of inputs, outputs and module function.