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Car AC turns on by itself

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Hi, I have a 2017 Mazda 3 Sport with 61,478 miles on it. The AC randomly turns on by itself and don't know why. I've taken it to the dealership multiple times and they can never find a problem with it. Can someone help me?

4 Answers
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Do you have the defroster outlet selected? The AC on modern cars engages with the windshield defroster. Other than that it sounds like a problem with the electronics.

I don't believe so. All the lights, except the air intake, are off and settings are set to zero. I've been thinking it could be electrical problems, but wouldn't it set off codes when scanning for them?

It depends on the type of problem and whether there is a sensor to pick up on it. Did the dealer thoroughly test the system using a bidirection scan tool or did they just do a quick go/no-go check for codes?

I'm not sure, they only said they scanned for codes and I never asked for more.

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Did you put the AC on automatic climate control?

No, I only have a manual climate control. The only thing that's on is the air intake selector, which I can't turn off anyway.

Apparently, Mazda has some issues with blower relay in earlier models. You may try changin the relay and see what happens.

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Do you recall any pattern or is it completely random? (ex. few minutes after start, cold temperature, hot temperature, humid climate, when you press ventilation buttons, with defrost, etc.)

It's completely random. Happens at night when it's cold, during the day when it's hot, a few seconds after starting. It usually turns itself off after a while, but I usually press the a/c button to turn it off

Well that's a strange yet funny thing for sure. If there is no code that means the computer thinks you are the one pressing the button, so the electrical problem is probably between the module and the battery. Could be a short, could be a bare wire, could be a lot of things. If you can turn it off by yourself, I'd say live with it and tell your passengers your car is haunted. The hours you'd have to pay for the mechanic to figure it out is not worth it in my opinion.

If you absolutely have to get it fixed, ask your dealer if they have a diagnostic mechanic (mechanic who specializes in diagnostics, not just any mechanic), I say dealer because he/she will know every possible mazda faults and problems. If he/she doesn't know how to fix this, nobody does. But if you've taken your car to the dealer multiple times then they probably don't.

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Based on what you said, I would suspect a problem with the AC switch itself randomly turning on the AC. You did say it works to shut it off, right?

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