Hissing Sound + sudden lack of coldness in cabin

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09-13-2011, 04:40 PM
MiataProtege

Hissing Sound + sudden lack of coldness in cabin

I drive a 1999 Miata, fully stock.

There is this hissing sound... it lasts for half a second and is just a "Hiss" which is terminated abruptly it feels... It tends to happen on one of two occasions... when my RPMs go a bit high (5500-6000)... or when I'm going up in RPMs and then let it drop without doing anything but letting go of the throttle.
It sounds a lot like this video
http://www.youtube.com/watch?v=Gn-Ao...eature=related
at the 53 second mark. It makes a very similar sound... I think thats a turbo blow off valve? But my car is not a turbo..... Any ideas?

Additionally... I was parked today... (unrelated I think).... and had the car running with ac on... I, until this moment, had been perfectly happy with the coldness inside of my convertible soft top... I turned on the defrost vents with regular AC just to play with the buttons.... a bit of pollen / grass debris came out (not a lot, just enough to see crumbs of stuff go on my dashboard and have to wipe it away) and upon driving home afterward... I noticed it was quite hot in my car. The AC was blowing very coldly as before... just now it was hot in the car. I'm not sure as to why.... Would love your thoughts. I am as usual worried about my car and am too ignorant to diagnose.
09-13-2011, 05:30 PM
POS Racing

Is it a Hiss or a quick chirp noise?
09-13-2011, 08:17 PM
MiataProtege

Quote:

Originally Posted by POS Racing

Is it a Hiss or a quick chirp noise?

It lasts only for a moment... I suppose it could sound like a chirp too.
09-13-2011, 08:46 PM
POS Racing

Like your A/C belt chirping which is pretty common my old '99 did the same thing a new belt cured mine. YMMV

Best way to confirm is drive it the exact same way with the A/C off if you don't get a chirp it is the belt.

As far as the A/C it was Africa hot this afternoon be happy it worked at all. ;-)
09-13-2011, 09:38 PM
Piff

Possibly low on freon? Sounds like it's time to have one of your knowledgeable friends slap some AC gauges on there and see if you're low. You can make a guess yourself without gauges if you follow the FSM, but that's not going to be a definitive conclusion.

Regards.
09-13-2011, 10:08 PM
MiataProtege

Quote:

Originally Posted by POS Racing

Like your A/C belt chirping which is pretty common my old '99 did the same thing a new belt cured mine. YMMV

Best way to confirm is drive it the exact same way with the A/C off if you don't get a chirp it is the belt.

As far as the A/C it was Africa hot this afternoon be happy it worked at all. ;-)

Upon further investigation... I've noticed the sound definitely comes from the A/C. It will make the sound when my RPMs are stressed and then released from the stress... or when I switch on and off the A/C.

I figure the on and off A/C part making noise is fine... but why does it make noise when my engine is "relaxing" from high RPMs?

Additionally, hopped in it tonight and the A/C was freezing cold again. I believe you're right that it was simply hot outside today. I've only owned the BLACK convertible for a week now, so I haven't had the heat yet.
09-13-2011, 10:19 PM
POS Racing

Quote:

Originally Posted by MiataProtege

Upon further investigation... I've noticed the sound definitely comes from the A/C. It will make the sound when my RPMs are stressed and then released from the stress... or when I switch on and off the A/C.

I figure the on and off A/C part making noise is fine... but why does it make noise when my engine is "relaxing" from high RPMs?

The belt is still slipping it doesn't care if your accelerating or decelerating the motor is still turning at high RPM.

That isn't normal to get any squeak from the belt.
09-13-2011, 10:30 PM
MiataProtege

Quote:

Originally Posted by POS Racing

The belt is still slipping it doesn't care if your accelerating or decelerating the motor is still turning at RPM.

That isn't normal to get any squeak from the belt.

You know... every time I ask a question on these boards you always seem to be there giving advice. Thanks. You're very helpful!

I think replacing an A/C belt... is a job I could potentially do. I think I'm going to give it a shot. Just gotta find the part! (o-o-o... O'reillys!)