With the summer months in full swing and your calendar chock full of vacation travel, you need the air conditioning in your King Air to be in top form. Now is not the time for a breakdown. The worst-case scenario would be a diagnosis of Black Death – a devastating condition that can wreck your A/C and necessitate the replacement of all components.
Black Death is yucky, disgusting gunk that gums up your A/C system, destroys your components and renders the A/C inoperable. Affected parts cannot be repaired; they must be replaced. Even the lines, if they cannot be flushed clean, must be replaced. This is a miserable and expensive process. Worse yet, the A/C compressor on the King Air 200 and 300 is on the right-hand engine. All the plumbing goes through the wing root so the right-hand leading edge must come off. And that’s just the beginning.
The crux of the problem is moisture in the system. A/C systems are sealed to keep moisture out. Whenever the system is “opened” to replace a switch or a component, a vacuum pump is used to remove all the air and the moisture from it before recharging the system with Freon.
Moisture – the mortal enemy
Freon becomes acidic when mixed with moisture. Acid corrodes the aluminum in the condenser, the evaporator and certain parts of the compressor. In aircraft A/C systems, the lines (tubing) are aluminum and they also corrode. Think of the black residue on your rag after polishing the aluminum wheels on your car or the aluminum spinners on your King Air.
That’s the black in Black Death. It eats away at an A/C system from the inside out. Corroded aluminum particles mix with the Freon and the oil in the system. This concoction is subjected to extremes of temperature and morphs into a thick, black sludge that, quite literally, chokes your A/C system to death.
Freon R12 vs. R134a
Some think Black Death only affects R134a systems, but this is not true. Black Death can bring down an R12 system, too, if enough moisture gets in it.
R12 (aka dichlorodifluoromethane) boils at -21.6 degrees Fahrenheit. R134a (aka tetrafluoroethane) boils at the warmer temperature of -15.34 degrees Fahrenheit. This is why R134a doesn’t cool as well as R12. Another difference is that R134a is slightly acidic to begin with. Adding moisture to R134a further increases its acidity. This could be why Black Death rears its ugly head more frequently in R134a systems – that along with the fact that there are fewer R12 systems around these days.
I was never a fan of converting R12 systems to R134a because R12 cools so much better. As long as I could procure R12 – good R12 – I kept servicing those systems. R12, although pricey, continues to be available today, but you have to search for a reputable supplier. That said, I must say the R134a systems in cars and airplanes today are greatly improved over the anemic systems when R134a first came on the scene.
Freon – the good, the bad and the pretty (colored cylinders)
Ten years ago, I had a customer who owned a couple King Airs with R12 systems. He chafed at the cost of R12 so he brought me his own cylinders of Freon to use when servicing his A/C systems. I knew that he flew frequently to Mexico and assumed his R12 was purchased there, so I was careful not to mix his Freon with my own and suffer possible contamination. In refrigerant circles, Freon from Mexico and other countries had a reputation for impurities that muck up A/C systems. I once heard that Mexican R12 had butane added as a filler. Pure R12 is nonflammable.
There is nothing wrong with recycled Freon, whether it’s R12 or R134a, as long as it is clean and pure. The air conditioning machines used by knowledgeable A/C technicians pull the Freon out of an A/C system and store it. The Freon is filtered during this process so it’s safe to be reused. These machines have built-in sensors to indicate when the filters need to be changed.
Anyone buying Freon must (a) be licensed to do so and (b) be very discerning. My trusted supplier weighs each incoming cylinder of R12 before accepting it to ensure it’s not tainted. Freon is heavier than air, so if any air is cut into the Freon to dilute it, the cylinder won’t weigh enough.
Watch out for Freon substitutes. They can become highly corrosive. They often contain methyl chloride, which turns more acidic with less moisture than R134a.
Since the beginning of time (or at least the inception of Freon) refrigerant bottles were color coded. R12 always came in a white cylinder. R134a came in a light blue bottle. I have a bottle of R22 in my garage (for older residential A/C units) and the cylinder is light green.
The one odd exception to this rule is FR12, also known as FRIGC. FR12 is R134a with butane added. It was designed specifically for older cars manufactured with an R12 system. Strangely, FR12 also came in a white cylinder.
Once, when purchasing R12, I got a cylinder of FR12 by mistake. When I looked closely at the cylinder I saw the word tetrafluoroethane. This threw me for a loop – what’s R134a doing in a white cylinder? Ah, well, I soon learned the cylinder itself is different. It has a funky, upside-down configuration unlike other refrigerant cylinders. When my trusted supplier found out I was mistakenly given FR12 instead of R12, they were mortified. They promptly rectified the mistake and reorganized their warehouse to prevent it from happening again.
Important note: FR12 was never certified for use in aviation, so don’t even think about it.
Additional note: The refrigerant industry has recommended phasing out color-coded cylinders in favor of a uniform gray-green color for all refrigerant cylinders. Flammable refrigerant cylinders will have a red stripe to aid fire and first responder personnel in differentiating between flammable and nonflammable products. However, many color-coded cylinders are still in circulation.
Gauges and machines
A set of specialized gauges is required for any kind of work on an A/C system. They are to an A/C tech what a stethoscope is to a physician. I can discern high and low pressure readings, suction and so much more from these gauges. Everything having to do with air conditioning begins and ends with them.
For King Airs, I needed gauges for R12 systems and another set for R134a. The attach fittings are specific to each type of Freon. The aircraft service ports, the Freon cylinders and the A/C machines all have corresponding fittings to one or the other. Nothing is interchangeable, which makes it impossible to accidentally put R134a into an R12 system.
An A/C recovery and recharge machine can suck the Freon out of a system, clean it by filtration, store it and charge it back into the aircraft after the necessary repairs have been made.
Mercury and microns – evacuating the system
A vacuum pump is used to evacuate the Freon from a system, then a stronger vacuum is applied to purge the system of moisture. This vacuum is left on for a longer period. Moisture boils more readily under vacuum, and once the moisture has boiled away, the dry air is pulled out by vacuum.
The King Air manual calls for a vacuum pump that pulls at least 29 Hg (inches of mercury) and 125 microns. A proper A/C machine in good condition meets this criteria. Back in the day, I had access to a vacuum pump that pulled 250 microns. I used this pump after repairing large leaks to ensure I got all the moisture out.
The manual also states the system must be left under vacuum for up to four hours. I tend to leave a King Air system under vacuum for much longer. Whenever possible, I leave A/C systems on vacuum overnight.
Open systems invite trouble
I’m very particular about not leaving the system “open” while waiting for replacement parts to arrive. After troubleshooting and identifying the problem – let’s say it’s a bad expansion valve – I do not remove the bad valve. I wait until I have the new valve in my hot little hand before I remove the old one. The system is only open during the time it takes to remove and replace the expansion valve. This keeps the amount of air (moisture) entering the system to a bare minimum, and this is crucial in the world of A/C repair.
If an A/C system were left open for a period of time, for whatever reason, I would automatically change the receiver-drier. It contains a desiccant. Receiver-driers come with plugs on both ends. I never remove those plugs until just before I install it; otherwise, the desiccant starts pulling moisture from the ambient air, reducing the effectiveness of the new receiver-drier.
For me, changing the receiver-drier is a good maintenance practice whenever an A/C system is “opened” for any reason.
Confession
I went to air conditioning school when I worked for an automotive shop during high school. In the decades since, I’ve worked on a wide variety of auto and aircraft A/C systems, but lucky for me, I’ve never dealt directly with a system infected with Black Death. I have consulted with several shops when they encountered it and walked them through the remedial processes.
My partner in crime for A/C troubleshooting and repair hasn’t dealt with Black Death in his long career either. (He was my source for the vacuum pump that pulls 250 microns.) Together we’ve worked on King Air A/C systems that others gave up for dead, but none with Black Death. Some of those King Airs lived in the desert, but others lived in coastal or humid environments.
Many might assume that the dry desert climate in which I’ve lived and worked for many years is the reason I never ran into Black Death, since the condition thrives on moisture. But I don’t know if that tells the whole story.
Here’s what I do know: My A/C buddy and I are on the same page regarding pulling vacuum – the more time, the better. When it comes to purging moisture from A/C systems, we routinely exceed the maintenance manual requirements for time under vacuum. And we’re vigilant on keeping systems closed until the replacement part is in hand, ready for install.
What can you do?
If your King Air is in the shop with an A/C squawk, don’t be in a hurry. Allow time.
Consider this typical scenario: Your A/C is inop and you have a trip coming up. You get your King Air to the shop at the last minute for a quick fix. They troubleshoot it and find the compressor is bad. They get a new one coming, but they know you’re in a hurry so they take the old one off in preparation for replacement. The system sits open for one to two days. The shop receives and installs the new compressor as soon as it arrives; then they suck the system down with vacuum for an hour or so. They check for leaks and find none, so they top off the Freon and send you on your way. Most likely your A/C will blow ice cubes, at least initially, but the door was opened for moisture to get into the system. This will hamper A/C performance down the road and increase your risk of developing Black Death.
If you find your A/C blows cold, then warms up, then gets cold again, get your aircraft to a shop immediately. In my experience, such intermittent cooling indicates moisture in the system. A/C techs can diagnose this with their gauges. If you’re really pressed for time or far from home base, you can have the A/C serviced with Freon as a stopgap measure only. Just don’t leave it at that. You are not out of the woods yet.
As soon as you can schedule it, put the aircraft down for a thorough check and fix of the A/C. Allow time for your system to be leak-checked and thoroughly evacuated. Request your system be kept closed while waiting for parts to ship in. Request that the plugs on a new receiver-drier be left in place until the moment it is installed. If you get any pushback on these suggestions, call me. I’ll be happy to assist in any way I can.
The good guys
Besides patience, you need a shop with a good A/C tech. Anyone can throw Freon in a system, but proper servicing and effective troubleshooting require specialized equipment, a good grasp of the principles of air conditioning and experience. A good A/C tech will have all three, plus they will know where to source quality Freon.
I’m in a pickle here, because there are good guys out there who know what they’re doing and they go by the book. I don’t want to give the impression that I prevented Black Death by going beyond the book requirements. That could be a factor but I don’t know it for a fact. I do know that extended vacuum time has worked for me and I don’t see a downside to it.
The bottom line is that an A/C system contaminated with moisture won’t function properly and if not addressed effectively, Black Death could develop. That is a risk you do not want to take with your King Air. Moisture in the system can result from a variety of situations: a humid climate, bad Freon, a leaky system, a system left open to the air, insufficient time on vacuum, a weak or faulty vacuum pump. Any of these factors could contribute to the rise of Black Death in a King Air A/C system.
Your goal is to keep your cool with great-running A/C. How do you achieve that goal? Get and keep moisture out of your King Air A/C system!