Did they give you a printout? If they did, please post the results. I much prefer a set of numbers over "everything is okay". Some inexperienced mechanics see SOMETHING for output current and call that "okay". If what they saw was only one third of what should have been found, that is not okay.
Next, you need to specify if you have an automatic system or manually-operated controls for the functions. If you have to slide levers or have mechanical push buttons to change between defrost and heat, for example, you likely have a manual system with no computers. If you have tiny touch-buttons or knobs that turn to make the selections, there will be a computer in the system and those usually have a power module that runs the fan.
Did you check to see if the wipers or other circuits cause the same symptoms?
You can monitor the voltage going to the fan motor too, and watch what happens when you turn on the head lights. If the voltage stays constant but the fan stops running, it is a ground issue. The head lights are grounded under the hood and have nothing to do with the dash board, but there are interior lights that turn on with the tail lights, and some of those might share a ground with the heater fan or control module. Check the voltage on the fan motor's ground wire. If there is anything other than 0.0 volts, that circuit must be repaired.
Friday, September 2nd, 2016 AT 6:47 PM