Heating systems and their related airflow components have been the subject of service bulletins from several manufacturers recently. Here are some quick examples in case one shows up in your shop. Each MAY be eligible for warranty or goodwill consideration for your customer; you’ll have to check with the dealer.
Chevrolet has noted that the electrical terminals on the relay resistor module may corrode on certain trucks equipped with manual heating and A/C controls. Covered are the ‘03-‘06 Avalanche and Tahoe, the ‘03-‘07 Chevrolet Silverado and GMC Sierra and ‘03-‘06 GMCYukon and Yukon XL.
According to the bulletin, fan settings may become inoperative or the blower may not stop when the ignition is turned off. Another clue might be a burning smell or smoke from the module area.
The cure is a new fan resistor and resistor module.
Nissan is watching certain models from 2010 and 2011 for a condition in which either the fan speed doesn’t agree with the control setting or the fan is too noisy. It’s a problem similar to one seen on last year’s Infinity QX56. Most of the affected vehicles are still under warranty, and depending on the exact problem, dealers will perform the fix of replacing one or more air-mix doors.
Audi says passengers in its Q7 TFSI 3.0 models may not get enough heat when the engine is at idle. The problems is caused by either an incorrect hose to the coolant reservoir or a check valve out of position in the vent hose. Replacing the hose and checking the position and fit of the valve cures the problem.