Air Condition

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xprsav8r
Posts: 22
Joined: Mon May 08, 2017 5:23 pm

Air Condition

Post by xprsav8r »

Good evening fellow Express owners.

Has anyone installed an AC unit into their plane? I have an Arctic Air unit that runs off of 12v. I've tried venting the exhaust into the empennage but there's not enough airflow or negative pressure to vent the air out of the aircraft. As a result, the condenser begins to freeze and the current begins to spike. If others have installed an AC unit, can you please recommend how you were able to port the exhaust out? I think I need an exhaust vent, naca duct, louvres or something but not sure if it's safe to cut somewhere in the empennage or elsewhere.

Thanks,
Roger
jchisolm
Posts: 97
Joined: Tue Jun 17, 2014 9:56 pm

Re: Air Condition

Post by jchisolm »

How big is the exhaust port? I found some round 3 inch louvered vents. I think I got mine from a big box hardware store. Look around where they have dryer vents or hvac supplies. You can search for "marine engine bay vents". I mounted mine in the floor behind the big aft bulkhead. The rule I was told was add a doubler the size of the material you take out. A 3 in hole would be close to 7 sq in. There are probably 4 layers (2 inside, 2 outside) of 7781 there so you are taking out 28 sq in. If you do a inch on each side of the hole you have a 5x5 layup or 25 sq in - 7 you take out. I would say a 2 layer 5x5 layup and then drill the 3" hole in the middle.

The air vents I found did not have mounting holes so I bonded them in with a mill fiber slurry. Mine also have a collar for mounting a hose. A trick for making a tube is to take a piece of PVC pipe. Wax the hell out of it with car paste wax. At least 3 layers of wax. 4 layers of bid over the pipe, cure and then you can pull the PCV pipe out. Some PVA release agent also helps.

I will probably cut my vents out and use some with mounting holes so painting and any replacement will be easier.

Remember to point them in the right direction. I was lucky and caught my mistake before the resin cured.
Joe Chisolm
Express CT builder
Marble Falls, Texas
xprsav8r
Posts: 22
Joined: Mon May 08, 2017 5:23 pm

Re: Air Condition

Post by xprsav8r »

Thanks Joe. If I recall, the exhaust port is 4 inches.

Actually, that's where I cut the hole: about 6" aft of the first bulkhead (behind the cargo area). I initially dumped the exhaust out there without any kind of scoop. I was advised by the local maintenance shop to install a 4" marine clamshell vent with the opening pointed to the rear. The idea is that the negative pressure would aid in sucking out the exhaust. This appeared to help on the ground, but not so much in flight. The condenser still freezes over and the current draw exceeds 40A (ideally, the AC will spike at 30A and drop to 20A continuous draw).

I then tried adding a bilge pump inline between the AC exhaust and the opening. That further improved ground trials and did lengthen the time in flight from 3-5 min to 10-15 min, but ultimately deriving at the same problem.

I'm thinking of trying a simple AC vent vs. the marine clamshell to sell if it'll exhaust better. I'm curious to know if you've flown your plane and which AC unit you've installed. Would you mind PM'ing me, Joe? By the way, I'm not far from you if you're in Marble Falls; I'm at KDWH in the Houston-area.
jchisolm
Posts: 97
Joined: Tue Jun 17, 2014 9:56 pm

Re: Air Condition

Post by jchisolm »

I dont have any AC plans (yet). I put the vent in to help cabin air flow.
Have you tried to contact Artic Air? They may be able to help.

If the evaporator coil is freezing up it could be low refrigerant (not likely in that unit) or not enough air flowing over it. The evaporator needs to absorb heat from the air flow over it. If there is not enough heat the coil will go below freezing and in your (our) humid climate, you get ice. Two things, cycle the AC so the coil can warm up, or increase the air flow somehow into the unit. I'm not sure how this unit gets the cabin air. If you are worried about the current spikes cycling the unit, you might try a way to mix some of the hotter exhaust air into the cabin air flow into the unit.

My $0.02 worth. I'm not a hvac person but have some experience DIY.
Joe Chisolm
Express CT builder
Marble Falls, Texas
jchisolm
Posts: 97
Joined: Tue Jun 17, 2014 9:56 pm

Re: Air Condition

Post by jchisolm »

I just looked at one of the manuals from http://www.arcticaircooler.com
The manual says you can program a "de-ice" time but the factory default is "off". It probably just shuts the compressor off for some amount of time. Some home hvac units will switch the refrigerant flow so the hot compressed liquid flows into the evaporator and de-ices it.
Joe Chisolm
Express CT builder
Marble Falls, Texas
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