Q: A/C control messed up.

asked by on February 02, 2017

Auto mode - A/C blows hot air from the bottom/foot vents even when it is 80 degrees outside. Not normal. Manual controls will blow correctly, however, if it is really cold outside the middle dash vents blow cold air from the inside bottom corners. Warmer air blows out from most of the dash vents. Also, if I turn the heat up to max only warm air blows - not hot. I've tried the different hot/cold settings from within the iDrive system. This was never needed prior to the AUTO mode function doing its crazy thing. I've been told it may be the controller. Weather has been relatively good so not very annoying, however, when it did get really cold it was a little uncomfortable inside. Also, the fan motor by the radiator runs at high speed whenever the A/C is on. Makes a very loud annoying sound at low speeds. This may be another problem caused by the controller. Any suggestions?

My car has 152000 miles.
My car has an automatic transmission.

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The system is controlled electronically and consequently the controller is a possibility. But, to condemn the controller, there is a long sequence of diagnostic steps (from the Factory Service Manual) that have to be performed. Typically, in diagnostics of this sort, a bi-directional scan tool is used to remotely command operation of the various HVAC modes. If the controller does not function as commanded by the scan tool, throughout the diagnostic sequence, at that point it would be condemned and replaced. There are also blend doors and a heater control valve which could be implicated in the problem you are describing. For example, if a heater control valve is sticking, along with a blend door malfunction, you could have hot air delivered at the same time that the A/C system is on. If you request a diagnostic on the system performed by a certified Mechanic, dispatched by YourMechanic right to your location, the responding certified mechanic will get this resolved for you. The diagnostic to request is HVAC system diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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