HVAC Afterblow Feature Enabled at the Factory

The Afterblow feature is now enabled from the factory on 2021 Acadia (Fig. 12), Blazer, Bolt EV, XT5 and XT6 models. Previously, the Afterblow feature was disabled when the vehicle was delivered to the dealership, but could be enabled using a scan tool.


Fig. 12


The Afterblow feature dries condensate water on the evaporator surface by operating the blower motor after the engine is turned off. Drying the evaporator surface aids in reducing odor from the air conditioning system.


Afterblow Operation

The Afterblow feature will run the blower motor for a short period at low speed up to four times if the following criteria are met at system-specified levels.

  • The vehicle must be off and locked
  • Outside air temperature must exceed a given level
  • The A/C compressor has run for a specified amount of time
  • Battery voltage must be in the normal range


It is normal for the Afterblow feature to operate with the vehicle off and will not cause harm to the vehicle or its systems. No repair is necessary.

Disabling or enabling the Afterblow feature can be performed using GDS2 (after software update GWH#10) by selecting the HVAC Afterblow Configuration function.



The most common causes of undesirable odors are:

  • Debris in the heater and air conditioning evaporator and blower module.
  • Microbial growth on the evaporator core.


In addition to enabling the Afterblow feature, odors can be reduced by checking that the fresh air inlet is clear of debris, the heater and air conditioning evaporator and blower module drain is not blocked, and the passenger compartment air filter is in good condition.


– Thanks to Tom Burlingame

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