High carbon monoxide levels…help!

[IntoTheVhoid]

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]

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.

[GeeBee]

Have you read AD 99-11-07?

https://drs.faa.gov/browse/excelExternalWindow/A6B3F7EC2F325C6486256A640057D7EA.0001

[N201MKTurbo]

That kind of makes the AC worthless. Taxiing and climb is where you need it.

[Brandt]

2 hours ago, GeeBee said:

Have you read AD 99-11-07?

https://drs.faa.gov/browse/excelExternalWindow/A6B3F7EC2F325C6486256A640057D7EA.0001

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. 

[Schllc]

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]

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]

Have you read AD 99-11-07?
https://drs.faa.gov/browse/excelExternalWindow/A6B3F7EC2F325C6486256A640057D7EA.0001

I wasn’t aware of this. Thanks.

[IntoTheVhoid]

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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