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I have a Nissan Sentra 2008 and my A/C broke in October of 2016. The AC would be off completely but strong hot air would still be coming through the vents. The only time it would stop is when the car is completely off.

It would get cold only when set to "low or above". Now the AC is fully dead and no air comes through the vents unless when I turn circulation off then only when I move forward I feel the air coming through depending on how fast I accelerate. So when I stop completely, no air comes through. But when I move forward, little air comes through.

Some of my friends say I need a new blower resistor because that controls the air flow or something and others say blower motor. I believe if I am moving on "no circulation" and the air is coming through the vents, then the blower motor is fine. Or that its just my vents are open and the air is coming from somewhere else. Please help me decide so I don't get charged for unnecessary fixes.

P.S. the blower motor is behind the dashboard in my car.

  • So just to be clear, you don't feel any air when in recirculation mode, regardless of vehicle speed? – Zaid Apr 6 '17 at 2:15
  • Yes when circulation is "yellow" or on, i don't feel any AC. But when its off and i switch that nob on the far right, which has like the "max or to go to your feet or both feet and chest etc" to ", to anything but" max" it works but only when i am moving. – Jon2713 Apr 6 '17 at 2:22
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It looks like that year Sentra uses a field effect transistor and not a traditional resister. It's referred to as the Fan Control Amplifier and controls the ground circuit of the blower motor. The power side is relay controlled and fuses 10 & 11 in the underdash fuse box should always be hot with the ignition on. There is some feedback control to the HVAC module, but it may not be your issue.

Check fuses 10 & 11 in the underdash fusebox. If those are OK than backprobe the blower motor connector and check for power on terminal 1. Check terminal 2 for a variable voltage, this should be 12v with the fan control knob on off and 5v or full ground on full. If that checks out replace the blower motor.

If you don't see a change in voltage on terminal 2 of the blower motor when adjusting the fan control knob than check for power on terminal 2 of the fan control amp and for ground on terminal 1. If you have power and ground replace the fan control amp.

To check the feedback circuit disconnect the HVAC module and check terminal 18 for 12v Key On Engine Off or Running.

If you see an open circuit on any of these tests than you have a broken wire, blown fuse or bad ground somewhere.

  • sorry i really don't know about cars to be honest so all you said was like learning a new language D:. Is there a video on this or something. – Jon2713 Apr 6 '17 at 2:39
  • @Jon2713 There may be, try hitting the blower motor with the fan control knob on. if it comes back to life replace the blower motor. If it doesn't you have to go through the diagnostic procedure or take it to a trusted mechanic. – Ben Apr 6 '17 at 2:43
  • its kinda hard because my car is made special in a sense because the blower motor is behind the dash board D: – Jon2713 Apr 6 '17 at 2:50
  • @jon2713 you're right i just looked it up. 5.4 hours. you should still be able to access the connectors though. you can also smack around the area to see if it comes back to life. – Ben Apr 6 '17 at 2:55
  • Ok so take apart the glove box and a the top left i should see the connectors ? so just smack the "blower motor" its self like 2-3 times and then turn on the car to test? Should i disconnect the battery or something? – Jon2713 Apr 6 '17 at 3:03
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Based on your description it seems to me that the blower isn't running. With recirculation mode off the speed-dependent air flow is probably fresh outside air.

This doesn't necessarily mean that your blower motor is kaput. Consider the following possibilities:

  • a blown fuse/relay
  • an open in the power supply (loose connection)
  • An issue with the fan speed controller (conflict between what you select and what the controller sees you selected)
  • excessive voltage drop across the wiring (nick in the wiring)
  • broken impellers in the blower
  • "With recirculation mode off the speed-dependent air flow is probably fresh outside air." you mean that the air i am getting is coming from the vents? – Jon2713 Apr 6 '17 at 2:52
  • Yes, that's what I meant – Zaid Apr 6 '17 at 2:52
  • So technically, if anyone turns off "circulation" the AC will stop and they will be getting fresh air instead of AC air? – Jon2713 Apr 6 '17 at 2:54
  • No, the A/C will still run but a greater percentage of the air will be from the outside rather than what is recirculated. Using the A/C to cool 100% fresh air is terrible from an energy efficiency point of view, so manufacturers will still recirculate a decent portion of air even when you turn recirc off – Zaid Apr 6 '17 at 2:59

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