Sweet smell in a/c ducts

Motorhead-45 · 08-31-2006, 05:18 PM

I need some help finding the source of a nuisance sweet smell I'm getting thru my a/c ducts. I initially assumed it was an exhaust smell working it's way through the heat ducts but even after removing the heater hoses from the heat exchangers to the chassis the smell persists. Both of the heat exchanger flapper doors under the car appear to seal up tightly when the heater is in the off position. I also checked the transmission shift rod bellows, the bellows for the speedometer wires and the throttle cable and everything looks good. Has anyone else encountered the same problem and if so where did you find the smell coming from?

ruf-porsche · ruf-porsche's Garage

Left over air freshener under the seat of the car?

Since you didn't replace the air cooled engine with a water cooled engine we can elimiate anti-freeze.

LOL

Jim Sims · 08-31-2006, 05:28 PM

Mice - something they've left in the ducting?

Motorhead-45 · 05:43 PM

Not an air freshener....it's definitely an automotive engine type of scent not unlike what I would think a crankcase ventilation system might smell like. No critters either. They would have their own "unique" scent. This is definitely "mechanical" if there is such a description for a scent.

I understood the 911 a/c to be a strictly recirculation type of system meaning it recirculates air already in the cabin rather than pulling outside air in. The only possible I could come up with is that somehow the driver's side return air duct in the tunnel might be pulling exhaust up into the a/c system from a leak at the rear of the tunnel but I'm not sure it's even possible and I doublechecked all of the bellows/seals at the rear of the tunnel and they are good.

I'm stumped....wife also says it smells like exhaust to her.

Jim Sims · 08-31-2006, 05:42 PM

Just went out and smelled a open bottle of PAG refrigerant oil - quess what (never bothered to carefully smell it before) - it smells sweet.

rfuerst911sc · 08-31-2006, 05:46 PM

I would open the smugglers box lid and look around for the signs of refrigerant/oil leak.

Motorhead-45 · 05:52 PM

That's a possibility Jim although I went out and grabbed by bottle of PAG that was used when I installed the Rennaire system a couple of months ago and both the wife and I don't think it smells sweet enough...at least at room temp it doesn't. I haven't smelled it at 34 degrees though! I've been wanting to pop the cover off the evaporator box and improve the evap to box sealing so this gives me the excuse to go there. I have a good electronic freon leak sniffer and it comes up zilch. Sounds like a weekend project.

Jim Sims · 05:53 PM

Warm it up a bit (high pressure refrigerant line is often hot until the expansion valve), then smell it. Also, hot or burning electrical insulation/varnish can sometimes smell sweet.

CliffBrown · 08-31-2006, 05:57 PM

Make sure the drain is open and free under the evaporator. Mildew can have a rude smell but I wouldn't call it sweet.

Motorhead-45 · 06:43 PM

The wife thought I was nuts pouring PAG oil into a shot glass and then sticking it in the microwave. I think she though I was going to drink it! Warmed it smells closer to what I think I am smelling through the a/c vents although it is kind of difficult to tell. Time to investigate the smugglers box for a leak I think.

I sure hope I find a loose fitting and not a leak in the evap forcing an a/c sytem tear down. It has been cooling very well since I finally got the Rennaire upgrade all sorted out and I hate to disturb it!

My two focus areas will be a visual inspection looking for a leak with evidence of oil and a thorough freon sniffer test. I'll also give a good sniff to the evaporator box motor...it's 26 years old and I've been using the heck out of it since getting the a/c working properly!

Motorhead-45 · 08-31-2006, 06:40 PM

I forgot to say thanks guys for all of the advice. It sounds as if I had myself convinced it was the other end of the car causing the smell when it may very well be coming from within the evaporator box. I'll let you know what I find.

randywebb · 08-31-2006, 09:48 PM

I'm thinking esters...

Jim Sims · 08-31-2006, 10:18 PM

PAG = Polyalkylene Glycol

randywebb · 08-31-2006, 10:52 PM

Huh - I thought it meant some special fluid made by Porsche AG

masraum · 08-31-2006, 11:13 PM

Antifreeze. Normally when you smell something sweet in a cars vents, it's a leaky heater core leaking antifreeze into the ducts.

What do you guys think??

JohnJL · 09-01-2006, 03:39 AM

Jim's first guess was mine too...

Marty Fareri · 09-01-2006, 10:58 AM

In a Seinfeld episode, Jerry had to sell his car to get rid of the smell....I know your problem is no laughing matter, but I just couldn't resist recalling that episode and sharing....

Motorhead-45 · 12:09 PM

It's actually a very very faint smell and is not always there...especially on cooler mornings. I'm headed to the garage now to investigate further.

With respect to cars and smells...anyone recall the Myth Buster's episode in which they put an entire pig carcass in a Corvette, let it ferment for a day or two and then tried to remove the smell? The myth they were trying to bust was that you could use cleaners, disinfectants and other household products such as Fabreeze to get rid of the rotting flesh stench. They ended up selling the car for scrap if I recall correctly.....MYTH BUSTED!

rfuerst911sc · 09-01-2006, 12:00 PM

I'm thinking the Corvette would have been sold for scrap anyway regardless of the smell!!!!

dentist90 · dentist90's Garage

Quote:

Originally posted by masraum
Antifreeze. Normally when you smell something sweet in a cars vents, it's a leaky heater core leaking antifreeze into the ducts.

What do you guys think??

Ahh, no one fell for it. Maybe next time.