Diagnostics
DIAGNOSTICSThe DCHA is fully addressable with the DRBIII. System tests include a Field Mode Test to activate the DCHA for diagnostic testing purposes. The DCHA Control will store up to three DTCs in its memory. If the Controller detects a new fault in the DCHA system, one that is not already stored in its memory, it will clear the oldest of the three stored DTCs, and it will store the new fault's DTC. If the Controller detects a reoccurrence of a stored fault, it will overwrite that fault's DTC with the most recent occurrence.
For vehicles equipped with Automatic Temperature Control (ATC), the AC Cooldown Test will also activate the DCHA for diagnostic testing purposes. The AC Cooldown Test is actuated with the DRBIII. The test checks A/C system performance based on evaporator temperature sensor input. It also forces the ATC to initiate a Cabin Heater Activation request when the vehicle is equipped with a Diesel Cabin Heater Assist (DCHA). The air conditioning related portion of this test will not run if ambient temperature is below 12 °C (53 °F). However, the forced Cabin Heater activation will occur even if the air conditioning portion of this test fails to initiate because test criteria was not met. The air conditioning related portion of this test will pass if the evaporator temperature drops 6.7 °C (20 °F) within two minutes of starting this test. Only air conditioning related messages display on the DRBIII after running this test. These messages will clear after paging back out of this test. Therefore, it is important to note all of the AC Cooldown test messages before doing so. Running the AC Cooldown test will cause the DELAY and Snowflake VF segments on the ATC to flash for 162 seconds. If the air conditioning portion of this test fails, the DELAY and Snowflake VF segments will continue to flash until the vehicle is driven more than three miles.