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Fan sound in cabin?

 
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  • 1 Post By tfilbo
  • 1 Post By Handy_Cruiser
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Old 06 Jan 2018, 05:06 pm
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Default Fan sound in cabin?

I was recently driving my daughter's PT Cruiser and I hear a sound that is similar to running fan. It is not the blower and it decreases when the Cruiser is accelerating. Does anyone know what is making the sound? Thanks
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Old 06 Jan 2018, 05:35 pm
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Default Re: Fan sound in cabin?

Where does the sound seem to come from...front, back, side..??
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Old 06 Jan 2018, 05:37 pm
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Default Re: Fan sound in cabin?

OK. On further research I think the sound is more of a hissing sound coming from the center air vents. When I shut the vent I can no longer hear the sound. I also think I can hear it coming from the passenger's side of the engine compartment when I have the hood up. Any ideas would be helpful. Thanks

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Last edited by tfilbo; 06 Jan 2018 at 06:03 pm.
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Old 06 Jan 2018, 07:05 pm
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Default Re: Fan sound in cabin?

Could this be a problem with the check valve that's used to actuate the recirculate door?
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Old 06 Jan 2018, 07:13 pm
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Default Re: Fan sound in cabin?

If the noise changes with speed and not engine RPM's, then it's likely in the drive system somewhere. The fresh are vent is located beneath the cowling in front of the windshield on the passenger side. Unless someone added the cabin air filter that the factory almost never installed, then it's an open hole into the HVAC system unless in recalculation mode. So sound from under the hood can easily be transferred.

If the noise does in fact change with speed and not RPM's, I'd start with the right CV shaft and right front wheel bearing and/or brakes, even a tire. If this is a turbo PT, there is a carrier bearing on the right inner CV shaft that has a high tendency to go bad. That could make the noise described. But the other items mentioned on the non-turbo PT can do the same.
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Old 06 Jan 2018, 07:27 pm
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Default Re: Fan sound in cabin?

Quote:
Originally Posted by Handy_Cruiser View Post
If the noise does in fact change with speed and not RPM's, I'd start with the right CV shaft and right front wheel bearing and/or brakes, even a tire. If this is a turbo PT, there is a carrier bearing on the right inner CV shaft that has a high tendency to go bad. That could make the noise described. But the other items mentioned on the non-turbo PT can do the same.
I can hear the hiss in park so speed is not a factor. Also when I rev the engine in park the hiss doesn't seem to change at all. When I'm driving and accelerating, the sound will decrease but will return as soon as the acceleration stops.
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Last edited by tfilbo; 06 Jan 2018 at 07:46 pm.
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Old 06 Jan 2018, 07:50 pm
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Default Re: Fan sound in cabin?

Quote:
Originally Posted by tfilbo View Post
I can hear the hiss in park so speed is not a factor. Also when I rev the engine in park the hiss doesn't seem to change at all. When I'm driving and accelerating, the sound will decrease but will return as soon as the acceleration stops.
That's most likely a vacuum leak. You see, in a normally aspirated engine, manifold vacuum decreases during acceleration and then catches back up when at speed. Most cars including the PT have vacuum a reservoir that helps smooth this out. But you may still get a substantial vacuum drop anyway if you have a vacuum leak like this.
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Old 07 Jan 2018, 06:23 pm
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Default Re: Fan sound in cabin?

Thanks for the info about the vacuum leak. I've been looking at the repair manual. Now I have a theory, which I am unfortunately unable to check because I gave the car back to my daughter.

Here's my theory. The recirculate air door switch controls the vacuum to the door by blocking the supply of vacuum or not.

When the switch is is the fresh air mode the vacuum is blocked at the switch causing the vacuum to leak nearby, perhaps in the switch itself, thus producing the hiss.

When the switch is in the recirculate mode, the vacuum is supplied to the door actuator and flows freely, thus the leak is less or nonexistent if in the switch itself. That would explain the lack of hiss in the recirculate mode.

I'll check this out when I get my hands on the car and post the results, probably next week.

I'm open to alternate theories. Thanks Again
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Old 15 Feb 2018, 05:11 pm
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Default Re: Fan sound in cabin?

I finally got a chance to investigate further. The hissing sound is definitely coming from the switch area. I've ordered a replacement. I'll update after I get it installed.
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Old 04 Mar 2018, 06:36 pm
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Default Re: Fan sound in cabin?

Problem solved. Replaced switch. The switch is nothing more than a piece of plastic that moves up and down when the control knob is turned, uncovering and covering holes. For some unknown reason this was not functioning properly and was creating a vacuum leak. I took a switch off a used HVAC assembly and put it in the original HVAC assembly. Problem solved.
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