Miata Mailing List: May 1997, Message #187
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From: 	"John Freas" <jfreas@gte.net>

Subject: Re: Is this normal? (first use of AC)

Date: 	Fri, 2 May 1997 09:22:13 -0500



Previously on Is this normal, Ryan Cramer <rcramer@di.net> said...



> I tried out my air conditioner for the first time today but noticed some

> strange things. 



Well, I can tell you that mine doesn't do that.



The whining noise could be anything from a loose belt (also cause for

burning rubber smell), to a dying compressor.  The decrease in power is

typical for A/C in a small car.  The compressor puts a fair load on the

engine, and that extra drag really shows, especially in the low-end where

the engine is not as strong.  Once you get the car rolling, it starts to

feel better, hence the perception that the load disappears in 4th.  Also

consider that like most any automotive A/C system, yours will disengage

under full-throttle conditions, so if you hammer on it, the compressor will

kick off and let the engine pull the car.



As to the marbles sound, like any car noise it is hard to accurately

describe pinging (see also knocking and detonation), but the marble

reference is pretty good.  The sound isn't terribly loud unless it's very

serious, but it does (to me) sound like it's coming from the front of the

car, not the back.  Of course sounds can telegraph around an automobile,

and I don't know that I've ever heard knock/ping/detonation (KPD) with the

top up, so it may be different.  The added load of the compressor with 14

degree timing on a hot day could possibly bring on some KPD under heavy

acceleration, but running 93 octane?  It doesn't seem likely.  Still,

things like a heavy carbon load might aggravate things.  If it only does

this under heavy acceleration, and it stops immediately if you back off the

gas a little, then I'd suspect KPD.  Have a mechanic or someone who is

familiar ride with you and lend a trained ear.  Don't let it go

undiagnosed, if it's really detonation it can hurt the engine.



	-John



------------------------------------------------

John Freas (jfreas@gte.net)

Red '90 Base #7690

Daytona Beach, Florida

Team Roebuck

Team Voodoo

Team "I have no idea what those dimple things on the windshield frame are

for."

------------------------------------------------





> First off, it did work quite nicely, nice frigid air, etc.

> However, when the air conditioner is on, it sounds like there is some

sort

> of whine going on in the engine bay, especially when accelerating in the

> 4000 rpm range. Its pretty loud. There is also a noticable lack of power.

> The pitch and intensity of the whine follows the rpms. But everything

seems

> to work. The lack of power disappears when accelerating in 4th gear--its

> like the power kicks in again.

> 

> Also, on hard acceleration, I hear a soft crackling marbles in a tin can

> sound. It sounds like its coming from the muffler. I've heard people

mention

> pinging, but I don't know if this is it. I don't know what pinging is

> supposed to sound like--I've heard it described as "marbles in a tin can"

> sound, but this was not very loud at all, but it did resemble that sound.

> FYI, i'm running 14 btdc on 93 octane supreme exxon fuel. 

> 

> Finally, when I pulled into the garage and got out, there was a burnt

rubber

> smell in the engine bay. Everyting looked in place though, didn't look

like

> any belts were wearing or anything. The smell soon disappeared. The smell

> could have been my tires considering how worn they are. (New tires on the

> next paycheck!)

> 

> Is this normal for the Air conditioning to cause this? THis is the first

> time I've used it, so I was a little surprised.

> 

> Thanks,

> Ryan

> ---

> http://www.di.net/ryan/

> 

>