Chapter 23 - Air Conditioning

Yes, I've listened to all the arguments. Nat even mentioned my air conditioning in a newsletter as an example of all the crazy stuff people put in their planes. Actually I have most of the other stuff he listed too. I figure my engine can push it and my wings can lift it. We'll see. My rational for adding AC is detailed in the modifications section. This section is not about why. It's about how.

Closable NACA ducts

When making the NACA ducts on the side of the nose I decided I wanted to be able to close the inlets to get that elusive extra 1/2 knot, and so I could use internal air rather than external. I cut the skin around the NACA shape, but left it in place with a half inch of glass at the forward end to act as a hinge. I hooked some stiff wire to the rear of the skin so I could open and close the inlet with a push pull action. Next, I glassed pieces of cured 2 BID above and below the inlet to act as the sides of the scoop when it was open.

Using modelling clay I fabricated ducts to feed the air to my Jaguar XJS adjustable air vents in the panel. On the forward end of these ducts I added inlets for the internal air. Note: I originally added the inlets on the sides, until I realized that the pipes would interfer with the radio stack. The wire connected to my closable scoop goes through a small hole in the duct and hooks onto an aluminum lever which is turned by a knob on the panel next to the vent. I painted the ducts with gold engine enamel which seems to work well on cured epoxy and makes the result look vaguely professional.

Time off for a Cozy visit

There seem to be a lot of Cozy projects starting up in South Florida. In the space of a week I've had three emails from new builders wanting to visit. Karl and Mike, who are just starting on Chap 4, asked if they could drop in one Saturday in Nov '02. They showed up in a small bus with a full crew. I asked "Where are the wives?". You can see the closed NACA scoop in this picture.

Making the box

As usual, I did things in the wrong order. I'd removed a squirel fan blower (why do they call it that?) from a honda civic a few months ago and decided to make a box around it. I found a large coffee can of about the right diameter and a carboard box for the base and made a 2 BID layup. I used 2 inch PVC pipe for the outlet ports. After cure I floxed some aluminum bent into a circle inside the outlet to give it some strength. Once cured I found a home for my box in the nose, forward of the passenger rudder pedals. Cool. Now all I need is an AC evaporator core and heater core that fits the box.

Getting the parts

Charlie Kuss, an RV builder and member of my local EAA chapter, is an auto AC guy by trade. He advised me to get all the parts from a small recent model import like a Honda. It's important to get parts from a car that still has freon pressure because the elements wreak havoc very quickly one the freon is released.

One day in November '02 I set out with my toolbox to hunt down the parts. I went to a local U-Pick breakers yard. On the way in I asked how much an AC evaporator would be. The guy said "about $40 - $50". I found a '90 Mazda 323 which seemed in good condition apart from accident damageand it looked like I could get at all the AC stuff, including the pipes. It took me about 4 hours to remove the compressor, condensor and evaporator along with all the pipes and attached gizmos. I also got the heater core. It's fun working on a scrap car because you dont have to remember how everything goes together, you dont have to keep all the nuts, bolts and screws, and it doesnt matter if you accidentally damage something else along the way. Most of the stuff came off easily. The real trick was the heater box which took me a couple of hours. I tried to remove it nicely, but in the end I simply demolished it with a hacksaw blade and a pair of pliers until all that was left was the two cores. No-one ever buys a used heater box anyway - right?

I put the pile of parts on a trolley and wheeled it to the exit. When the "pricing" guy asked what I had, I responded "Air conditioning for my airplane". "Really", he says. "I'm a pilot too. What are you building?" A half hour later, after we'd swapped hanger tales and discussed the 13B in detail I asked - "so what's this lot going to cost me?". My new buddy Gerry sniffed at the trolley and said "$75 sound fair?". "Very fair", I said, and happily loaded the stuff into my trunk. I caught hell when I got home. I had cuts and scratches all over my hands and dried blood on some of the parts. I hadnt noticed the cuts while I was working.

Planning the installation

The first job was to weigh everything and see what kind of penalty I'd be paying for comfort and quiet in the cabin. I piled everything on the scale. The total was 33lbs. Individual components weighed as follows:
Condensor   5 lb
Evaporator  9 lb
Fan         1 lb
Compressor 18 lb


The evaporator core was a bit bigger than I'd hoped. It's about 8.5 * 9, rather than the 8 * 6 I'd built my box. Ah well. No big deal. Epoxy can always be adjusted. The real issue is where to put the sucker. I need the evaporator, heater core and blower all in the same area. After considering the baggage area, the hell hole, behind the front seat, under the back seat and various other places, I finally figured out a way I could mount everything in the nose. I'll have to move the brake master cylinders, but It looks like it can be done. The evaporator will go on one side with a duct across the middle to the box with the heater core and the blower unit box. This way I can run the heater and the AC at the same time. I remember using the heater to help cool old cars on a hot day. Uncomfortable, but it worked. Maybe I'll be able to do the same in my plane. If I run both maybe they'll cancel each other out.


My initial plan was to make a valve / door of some sort which would direct air to the floor, the vents or the defrost. In the end I went with a very simple method. I put three 2 inch outlets on the blower box, one for each vent and one for the defrost. For the floor control I added a door operated by a push-pull cable. Control will be by manually shutting of the vents and defrost outlets, and or by pulling the cable for the floor outlet.

For heater control I'll install a push pull cable and a valve in the engine compartment to adjust or shut off the hot water supply to the heater core. I'm not sure how to adjust the AC yet. I guess it involves switching the clutch on the compressor. There was a temperature probe embedded in the evaporator core. I put it the freezer and tested the solenoid. Sure enough it goes off when cold and comes on when warm (that's as accurate as I got). OK. This baby will connect in series with my switch and send power to the compressor clutch. I can easily wire this circuit in series with a full power microswitch, but I think I'll set it up manually via a check list for now. Obviously the first few flights will be done with AC off. Later, one of the flight tests will be to see how much power I loose with the AC on and how that impacts take off. I should have at least a 50 HP edge over an IO-360 powered Cozy. If I give up 5 or 10 HP to the AC I should still be well ahead of the game. Maybe "AC off for take-off" will only be required on a short field, or a very hot day at high elevation. We'll see. At least the first stage is done. The AC unit is installed and the blower is wired up. Now all I need is a few pipes....


I need four pipes from the nose to the engine compartment for freon and hot water. I also need a vacuum pipe. After walking around the plane, climbing in and out of the back and crawling around underneath I came up with a plan. I ordered 25 ft of 5/8 3003 al pipe and decided that the only way to install it was through the nose wheel cover into the heat duct. I removed a chunk of the nose wheel cover and proceeded to stuff the pipe up the heat duct. It got as far as the "bump" over the gear legs. I removed the circular fiberglass pipe I'd made back in chapter 8 and extended the hole in the forward gear bulkhead downwards about an inch. With a little persuasion I was able to get the pipe all the way back to the the firewall. The back end of the heat duct comes out under the radiator inside the plenum built into the lower cowling. I'm going to have to figure a way to get the pipes from there to the various orifices without interfering with the airflow.

Once I'd got two 5/8 pipes inserted I cut oval holes in the sides of the heat duct under the front seats, pulled the pipes through until they lined up with the holes and deftly snagged them into the cabin. With Char pushing from the firewall, and me pulling from the cabin we gradually persuaded the pipes to curve gently into the area under the seat where I could add connections. Since one goes to the pilot side, and one to the passenger side, these pipes will be the AC return to the compressor, and the heater feed.

A word of advice for those working on Chaper 8 who plan on using a water cooled engine.... Install you're pipes now, while you're building the heat duct. Once the pipes are in you can fill the whole thing with pour foam for insulation before closing it up.

Here you see the heater pipes heading along the left side. In the distance is the left side of the heater / AC / Blower box. The scat tube ducts are all in place except the lower one which will be tied up out of the way later. I'd bought some automotive heater hose, but decided that 5/8 3003 AL pipe would be better if I could get enough of it down the heat duct. I had two pipes installed, and it looked to me that I could get the other two in as well. I ordered some more. In the meantime I worked on the connections at the front. The heater core had two hose connectors coming straight out of the side. I had set this up to point downwards, so I needed to install 90 degree angles and some sort of screw up fitting. I used 1/2 inch copper 90's with a short piece of 1/2 copper pipe into a male compression union. I soldered the joints the same way I'd done when installing copper lines for my home air conditioning. If it worked there, then it should work here. Right?

This is the heater pipes and flow control valve seen from the front. The pour foam insulation is forming between the metal duct tape guides.>
<IMG SRC = The last large pipe was interesting. This was for the vacuum. With a certain amount of gentle persuasion I was able to insert the pipe into the heat duct through the nose well. I got it all the way back to the gear well, bent it around the gear and inserted it in the "back passage" a couple of inches. There seemed no way to budge it from here. I pulled, twisted, pushed and wiggled it to no avail. Admitedly the heat duct entry in the firewall was getting a bit full of pipes by now, but it looked like there was room. I hit on a plan. I drilled two holes across the end of the pipe and inserted some steel rudder cable. I hooked this up to my "comealong" which I attached to a stansion holding the patio roof. No. I didnt pull the roof down, but I did pull the plane backwards. OK. I have a parking brake! I set the parking brake and pulled again. The plane skidded on the tires. OK. I got a 2 * 4 and braced the engine mount against the bottom of the stantion to form a triangle. Now the pipe began to move. In no time I pulled the pipe through the hole and out a foot or so behind the firewall. i was quite pleased with myself until I inspected the pipe. It was flat on one side. There was no possible way to get a fitting on there. I folled the pipe forwards until the flat side dissappeared as the pipe went over the gear. Of course. I'd been pulling soft aluminum against hard fiberglass. The aluminum had flattened. Duh. I cut the pipe off where it entered the gear well and pulled, wiggled and pushed some more. I "adjusted" the hole into the firewall a bit with the dremel and eventually got the fourth pipe into the engine compartment without damaging it on the way. The forward end of the pipe ends just in front of the panel. I attached a right angle fitting there to connect to the vacuum hose, filled the gap with pour foam, sanded it flat, then sealed off the gear well with a fiberglass patch.

A little later I realized that my right angle fitting was pointing towards the pilots feet, so the vacuum hose would have to run across the floor. Damn. That doesnt make sense when all I had to do was run it vertically up behind the panel. I cut away my nice fiberglass patch, dug out the foam and rotated the vacuum fitting 90 degrees. I lowered the vacuum hose down behind the middle of the panel and screwed it into the fitting with teflon tape. More pour foam and another fiberglass patch finished the job. The vacuum hose now sticks up a few inches above the gear well cover where I attached a T fitting to split it between the attitutde indicator and the DG. I'll need a plastic right angle fitting to feed the air from the filter to the DG, and a straight one for the AI. Why straight? because it's impossible to screw right angle fittings into both holes on the AI - one hits the other and can't turn. Seems like a simple problem, but it means I have to wait for some more fittings from Wicks before the vacuum system is done. Then, of course, there's the engine end.....

All I had left was the 1/4 al 3003 pipe for the AC freon feed. The four 5/8 pipes made a square, so my theory was that the 1/4 pipe would fit in the hole down the middle of the square. The theory worked until I got to the rear cabin where the pipes went down below the rear seat belt attach point. I didnt want to damage the structure around this area, so rather than force the issue I ran the remaining pipe along the top of the heatduct, through the seatback, then down under the co-pilot seat to condenser.

AC Connections

Behind all the wires you can see the AC pipes heading up the right side. It took a bit of figuring out, a couple of trips to the hydrolic's store and one extra trip to the junk yard, but I ended up with connections that shouldn't leak. The stock AC pipes for a Mazda 323 are 5/8 OD for the return and and 1/4 OD for the feed. I simply cut the ends off the stock connectors and used my flaring tool to put on AN fittings. I then used AN unions to splice the 5/8 and 1/4 al pipe from Wicks to effectively extend the length of the stock pipe. Where the stock pipes had attachments, like a bleed fitting or a solenoid I made sure I kept these. This was one of those jobs that took three weeks, but can be explained in few words... and could be done in 2 hours the second time around or when done by someone who knew what they were doing.


here you see the work in progress under the seats. The heater pipes are already covered with pour foam. On the right side are the freon pipes. After trying various pipe insulation sheaths from Home Depot, I decided that the best way to insulate the pipes was pour foam. I sealed the ends of the heat duct, tipped the plane on its back and poured the mixture down the heat duct. After a few seconds foam appeared from all the little holes and unsealed joints I'd missed, then came out the front end into the nose gear well. My heat duct was now totally full of foam. Next I made channels around the pipes with metal duct tape and poured more foam into them to form a Y under the seats and cover the pipes all the way to the panel.

Heater and AC pipes insulated under the seats. It looks like a mess here, but it cleaned up nice. This was another of those times where the plan evolved. Once the pour foam was cured, cleaned up and carved into a "pleasing shape" I decided that it needed covering to stop the gritty foam getting damaged and spreading around. Once that stuff gets loose it gets everywhere - I know - our bed has been full of it on numerous occasions. So, 1 ply BID covered the foam nicely. I made bumps Where the freon feed went down the right side, and a bundle of wires went down the left side of the center console. Here's the finished product with zolotone finish. Now you see it. Now you don't. With the seats in place everything is hidden and out of the way. Note my throttle quadrant and center console are taking shape. That's Tracy's EC2 control panel set on a slant with a walnut backing. The armrest is removeable.

At last all my connections were done - in the front. All I have to do now is connect the other ends to things in the engine compartment.

Ripping it all out again

Ugh. It didn't take me long to realize that my pipe installation was a complete and utter clusterfu.k. Every time I looked at the back of the plane I knew - those pipes are gonna have to be redone. Whenever someone looked over the plane I'd point the pipes out and mention that they were going to be changed. Apart from being kinked and flattened, the pipes arrived behind the firewall in the wrong damn place, right in the middle of the plenum where they'd disrupt airflow and be susceptible to FOD. What WAS I thinking?

I was dreading the job, but eventually I had to tackle it. I cut the pipes off where they entered the landing gear box and removed one side of the rear heat duct so I could bend them out enough to put fittings on the ends. Removing the pour foam was a pain, but eventually I got the pipes out. While I was at it, I revised the fuel pipes as well. They used to run over the landing gear box to the filters behind the back seats, then on through the firewall. I'd recently had a conversation with another builder who had had a fuel vent pressurize and dump a couple of gallons of gasoline into the back seat area. Scary. I decided it might be better if the fuel pipes headed out of the back seat area as quickly as possible. Now all the heater and AC pipes were out of the way I could run the fuel pipes into the LG box and mount the filters centered above the gear with plenty of clearance. Much better. I floxed nutplated to the top of the gear well and used those rubberized clamps to hold the filters in place. Ugh.

The next job was to reorganize the metal pipes. I got some more pipe and -10 bulkhead fittings and proceeded to make connecting pipes with 5/8 6061 aluminum. After a day trying I decided that I needed flexible hose for these connections. The Aeroquip hose I had is good to 250 PSI, but it doesn't support freon, so I used aluminum for the AC return. I got the AN push on barb type fittings for the hose. The price of all these fittings has numbed me to the point that I don't even ask anymore. Rather than worry about it I've taken the attitude that it's like gasoline. I have to have it, and I'm not going to buy less because of the price. Just show me where to sign, and give me the stuff I need.

I installed the Aeroquip hose in no time. Much better. Tom, who's building a Glasair a couple of hangars down the row, stopped by and noticed the seven bulkhead fittings sticking through my firewall. "What's all these?" he asks. "Well, there's two for water, two for freon, two for fuel and one for vacuum", says I. "Hmmm. I only have one for the fuel pipe", he says. Maybe there's something in this KISS thing after all.

When the connections were all tight I persuaded the pipes to go back where they belong and got ready to repair the heat duct. I cut a piece of scrap fiberglassed foam to shape and floxed it in place. It was late evening, and the light in my hangar is one of those opinionated type that gets overheated and shuts itself off to cool down. I wish I could do that. No problem, though, since I have my handy inspection light hooked over the turtleback so I'm getting lots of light. I'm busy with the second of six plys of BID when the overhead light decides to take some time off. At that point I knocked the inspection light off it's hook. Darkness.

Oh. This is great. Here I am with gloves on, crouched in the back of the plane. I have precut BID, flox, brush, heat gun, plastic and epoxy at the ready and I'm half way through stippling my second ply. Pitch black. Can't see a thing - not even to put stuff down and get out of the plane. I wait the prescribed minute or two while the lazy damned light took a break, and then there was light. Whew. I stippled, added another couple of plys, reached out for the epoxy cup. Darkness. This is getting to be very annoying. Eventually I completed the layup in spurts intersperced (can you say that quickly) with periods of total darkness. I went home, with a reminder to myself to bring spare bulbs, hoping the layup came out ok.

The pipes come together

Better I managed to get all the pipes to fit under the rear center console without too much trouble. When I rebuilt the rear part of the armrest support which goes from the rear floor up to the spar I built it in two halves for ease of access to the pipes and connectors. Each half is secures with sheet metal screws. When the upholstered center console piece is fitted over the top everything is solid and well hidden. I'd just finsihed off the back seat area when Roger from Japtrix mentioned that the heater feed is on the pilot side of the engine, and the return goes to the water pump. I wanted my valve on the feed, but had thought that the feed came from the pump. I climbed in the back once again and reversed the pipes. Done Now the pipes are redone I swear I'll never get in the back of this plane again. At a rough guess I've climbed in and out of the back 8,000 times, and crouched in there for a total of 34 hours. For those who wonder how hard it is to get in the back, I have the entry and exit down to a fine art. One foot on the step, one knee on the strake and you're in. To get out, turn around, sit on the strake, swing you're legs around and put a foot on the step. You're out in seconds. I bet I could get in, sit down and get out again in less than 5 seconds. Don't take the bet. I'm never getting in the back again. Except to fit the ELT and the headset jacks.....oh and maybe to fit that new cushion and adjust the headrests....and to charge the battery...and to clean the epoxy off the rear windows....and....
By the time I'm done with this plane I'll have done amost everything at least twice.


I left installing the compressor (from a Mazda MX3) until a lot of other stuff, including the intake was done. It didnt occur to me that the intake would interfer with the compressor mounting spot. By good luck it doesn't, but the throttle body does, and the throttle cable is going to have to move. I should have had the intake made a little higher at the front (firewall end). There's no way that the stock compressor will fit in the space left between the engine mount and the bottom of the throttle body, but I think I can get the smaller Mazda MX3 compressor in there, which is fine because I don't need the weight or power of the stock unit. I made a bracket out of 1/8 aluminum to see if everything will fit. It's REALLY tight, but I think it'll work. I had to "trim" one of the legs of the compressor to get it under the lip of the throttle body, but otherwise it seems fine. Next I ordered a 9inch square of 1/10 thick (that's 100/1000) 4031 steel from Wicks. The bracket needs to be bent so that it can be located on four bolts, two of which are on one level and two on another 3/8 further toward the centerline. Bending the aluminum template was easy. Bending 1/10 tempered steel isn't. Charlie took one look at it and told me I need to go see Bill at American General Steel. Bill has a massive bending machine and accomplished the task in a few seconds. I cut and drilled the bracket and installed the compressor. Three things were obvious. First, the fit is very tight. I have maybe 1/8 clearance around the compressor, and I'm not sure it's going to be enough. Second, there's no way in hell the big AC line connectors are going to fit, and third, I need some kind of idler pully to keep the belt tight. Aghhhhhhh!


I found a home for the condensor on the starboard side out towards the wing root and made a duct for it, just like the intercooler duct. The condensor has it's own air bleed off the plenum. The next issue in this area is going to be the pipes from the compressor to the condensor, and the dryer. One step at a time....


At this point I started my launch countdown. One of the bigger tasks was fitting the compressor which is documented there.


I finally got the compressor installed. I consulted with an AC expert and was informed that my AN fittings will never hold the new freon. He said it would be a waste of time trying to pump it up. I was getting close to first flight so, reluctantly, I decided to leave the AC off until the plane had flown the initial testing was complete. At some point I'll get around to refitting the compressor, changing the AN fittings for AC ones with O rings, and getting the AC system up and working.

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