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High carbon monoxide levels…help!

IntoTheVhoid
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IntoTheVhoid Rookie

IntoTheVhoid

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Hi all.
I have a 1998 Ovation.

Recently bought a Lightspeed Zulu headset with inbuilt CO detector. Also have a CO guardian unit, CO sensor inside my ForeFlight Sentry and a dash mounted ASA CO detector. Safe to say I’m covered for CO detection! But it was the audible realtime CO level announcements in the Lightspeed that alerted me to high CO levels (>50ppm, up to 100ppm) in various stages of flight. 

After testing, we’ve isolated the issue to the airconditioning unit blower and overhead vent/mixer. It seems we are sucking exhaust at the tail through the inlet back there, and reticulating it through the cabin when the blower is on and vents are configured to do so.

To complicate issues, I’m also getting high CO levels when taxiing, when A/C is off and vents are closed. 
 

Having the “silent killer” at unsafe levels in my cabin with wife and kids is concerning to say the least, and we’ve grounded the bird until we can work out what to do. 

Everything in front of the firewall is looking immaculate, no cracks or anything, and I’ve recently had a new (factory remanufactured) engine installed, new hoses, etc.

Has anyone had CO issues with Ovations, particularly ones with A/C? 
 

Would appreciate any tips or guidance.

 

N201MKTurbo Grand Master

N201MKTurbo

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I’m not familiar with the Mooney air conditioning system. Where does the condenser get its air from? Where does it exhaust it too? Where is the evaporator air return? 

I’m thinking the condenser is sucking in exhaust and instead of blowing it overboard, it is getting into the tail cone. Then it is either getting into the cabin from the tail cone or there is an air leak in your evaporator circuit.

Schllc Veteran

Schllc

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People are reluctant to believe, but in slow modes, ground and climb, the doors are incredibly leaky. It becomes a vacuum when you go faster so it’s not a problem, but that is the simplest and easiest place to start. 
I can’t imagine how it would be the condenser because it’s simply a heat exchanger and has no connection to the interior.   Not saying it’s not possible, just not likely.

exM20K Veteran

exM20K

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22 hours ago, Schllc said:

People are reluctant to believe, but in slow modes, ground and climb, the doors are incredibly leaky. It becomes a vacuum when you go faster so it’s not a problem, but that is the simplest and easiest place to start. 
I can’t imagine how it would be the condenser because it’s simply a heat exchanger and has no connection to the interior.   Not saying it’s not possible, just not likely.

In the climb, it’s all working against you. Full power, ROP, high AOA, etc.  35GPH in a 310 HP Acclaim is definitely producing a high volume of CO.

In both my Mooney’s, the bottom rear corner of the door sealed very poorly.  This creates a Venturi-induced low pressure in the cabin, which draws in the dirty exhaust. I had the door seal replaced at annual and a 1/4” gasket run around the cabin door seat, and noise and CO in the climb are much better.

The tail cone and avionics bay are also (relatively) low pressure.  Dunno where the factory gets its fresh (return) air from, but this could be part of the problem.

 

I don’t think the A/D applies to the Kelley Aerospace electric units, but it probably should. Heck, even just using a B-Kool in the climb out can get the levels up over 50min my plane (before new seals.)

-dan

IntoTheVhoid Rookie

IntoTheVhoid

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Might be worth calling Mooney or Don Maxwell and asking what modifications they made for later aircraft.  I can use my a/c in taxi and climb.  Zero CO. 

Good idea. We were thinking it must be a design fault (as confirmed by the AD), and that an engineered solution (modification) might be possible.


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  • 1 month later...
Pinecone Grand Master

Pinecone

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FYI, the OSHA limit for CO exposure is 50 PPM for a 8-hour time weighted average.  This means that you average the CO level over a normal 8 hour shift.

So 100 PPM is OK for up to 4 hours per day, 200 PPM for 2 hours.  If the exposure is longer than 8 hours, the allowable level is lower.  So for a double shift (16 hours) the max average is 25 PPM..  NIOSH does recommend a maximum exposure concentration of 200 PPM.

All that said, I would not worry too much about a 100 PPM during taxi or even climb.  But would worry about a level that high in cruise.

IvanP Rising Star

IvanP

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Posted
4 hours ago, amekler said:

On our bravo installing a Bob fields inflatable door seal fixed my problem 

Alan 

@ameklerHow difficult was the install? My door seal is not great (OEM installed over a decade ago and torn in couple places) and I am deciding between Brown's and the inflatable. What is your overall satisfaction with the Field's one? TIA.

Schllc Veteran

Schllc

Posted
Posted
4 hours ago, IvanP said:

@ameklerHow difficult was the install? My door seal is not great (OEM installed over a decade ago and torn in couple places) and I am deciding between Brown's and the inflatable. What is your overall satisfaction with the Field's one? TIA.

You will not believe the difference until you hear it for yourself. 
it is extremely easy to install. 
it will take you more time to remove and clean the old seal. 
I opted for a manual inflate, for price, weight and simplicity. 

Schllc Veteran

Schllc

Posted
Posted
6 hours ago, IntoTheVhoid said:

Great tip, thank you, but unfortunately it seems they don’t do one for my M20R.

Yes they do. The door seal for the k fits. I installed it in my acclaim.

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