Maintenance Tip: Keep Your Cool – Notes on King Air A/C

It’s August and it’s hot, at least in my part of the world. So far this season, I’ve dealt with everything under the sun and in the shade when it comes to air conditioning (A/C) problems. I’ve solved these issues by looking first at the usual suspects – compressors, vent blowers, and low refrigerant levels. In other cases, it was the less common – condenser and evaporator.

Air conditioning is a topic unto itself and either you get it or you don’t. There are plenty of very capable A&Ps out there who will tell you right off the bat that they’re no good when it comes to air conditioning. Have respect for those guys; they are doing you a huge favor with their honesty. Unfortunately, there are some who say they can fix anything, but who really don’t know what they are doing when it comes to air conditioning. Things can go from bad to worse more quickly than you would think, as in example B below.

Example A: The A/C is not working in a King Air. The compressor is found to be bad; in fact, it blew up (see photos)! Debris went through the system to the receiver dryer. We removed the compressor and the receiver dryer, flushed the system between those two points then removed the flush. We then installed a new compressor and receiver dryer, and replaced a couple other items as needed (belts, current limiter). Next, we serviced the system with the proper type and amount of refrigerant. It ran great on the ground run.

Example B: Another King Air’s A/C is not working and its compressor, too, is found to be bad. The compressor was removed, the system was flushed, a new compressor was installed, but the A/C just blew hot air. The Freon level looked fine, and the shop wasn’t sure what to do next, so they began replacing components. Eight thousand dollars later (yes, $8,000!), the shop told the owner the next step would be to gut the interior and replace each and every line in the system; also to replace the evaporators and the condenser in order to find and fix the problem. Their estimate for this project was another $15,000. The owner refused this offer.

He brought the aircraft to me and we found the receiver dryer totally plugged with flush. When they flushed the system, they had flushed the whole system, including everything downstream of the receiver dryer! After drowning the system in flush, they failed to get it all out. It took three more receiver dryers to capture all that residual flush that was mucking up the system. Finally, once the system was completely purged of flush, we were able to properly service it with the correct type and amount of Freon. It’s been blowing icicles ever since.

What’s Driving It?

It’s one thing to understand the principles of air conditioning, but that’s just the beginning. King Air A/C systems are a bit convoluted. I hate to say it, but the A/C in a King Air is not its strongest point.

If you have a model 90 or 100, your A/C is driven by an electric motor in the nose. If you have a 200, 300 or 350 model, your A/C is driven by the right-hand engine. Three years ago, I wrote an article for this magazine on troubleshooting air conditioning problems; it was focused strictly on the engine-driven systems in the 200s/300s/350s. If you missed it, look for the May/June issue of 2012.

Electric Motor-Driven

Air conditioning in the King Air model 90s and 100s works pretty well as far as cooling the cabin is concerned. Plus, while you are pre-flighting the aircraft, you can plug in external power and run the A/C on the ground to pre-cool the cabin before the passengers arrive. This is positively blissful in triple digit temperatures. Another perk? It’s easy to troubleshoot the system – just plug in the GPU.

The problem is the huge load this electric motor draws off the generators. Today I was performing a routine ground run on a C90. The generators were showing 15% until I turned on the A/C; then they showed 40% per side – quite a load. Beech was concerned that in instances of losing an engine, a massive load would be born by one generator, leaving little room for everything else needing juice in a clutch situation.

Another concern was that the motor-driven A/C worked hard all the time. That motor is either on or it’s off. When it runs, it is always at the same speed, providing optimum output continuously, so these motors can wear out.

Early 90 and 100 models had a two-cylinder compressor. This was later changed to a five-cylinder compressor which used the same amount of juice off the generators, but it made colder air and it made it faster. No complaints there.

Engine-Driven

With the advent of the 200 series King Air, and the 300s and 350s that followed, Beech desperately wanted to shed the generator loads so they ran the A/C system off the right-hand engine. While on the ground and running, the condenser blower draws 40-50 amps, but as soon as you break ground, the condenser blower shuts off. The moment you are airborne, the scoop on the right side of the nose puts air across the condenser and that air cools the Freon.

Once in the air, the draw on the generators from A/C-related components is negligible. You would think that condenser blowers would last much longer in the engine-driven systems because they only run 20-30 minutes on the ground and never in the air; whereas the motor-driven systems are going on the ground and in the air (at least until your OAT goes below 50º F). In my experience, the condenser blowers in a 200 wear out as fast as they do in a 90. Go figure.

Automotive Ancestry

The A/C in the early model 200s had a six-cylinder compressor. It was an A6 compressor like those found in a Cadillac Coupe de Ville or a Chevy Monte Carlo. They worked pretty well considering they were cooling 12 feet of aircraft cabin – way more cubic feet than the automobiles for which they were designed. The A/C on all King Airs has its roots in automotive systems.

One of my favorite stories concerns an A100 owner out of Utah. He was in Las Vegas on business on a really hot day in June, and had no A/C. He heard about me and hopped over to my location. Right away I determined the system was out of Freon. I serviced it and got out my sniffer. Sure enough, I found a substantial leak at the compressor drive seal. While the owner fretted over an expensive part from Beech and time involved to ship it, I had other ideas.

I knew from experience that a Ford F-150 had the same compressor. Remember the two-cylinder on the early 90s and 100s? In the days of yore at Beech West in Van Nuys, I used to rebuild those compressors with a kit from the auto parts store. So I got on the phone and found the seal I needed at a freightliner dealer across town. My wife zoomed over and got the part, I installed it, and he was good to go. I think I charged him $30 for the seal. He was flabbergasted that I knew what to do and ecstatic that I saved him so much money. We became friends on the spot. When he bought a second King Air, he brought them both to me for as long as he owned them. To this day, we get a good chuckle over that one.

Engine-Driven System Decreases
Cooling Capacity

Although happy with the engine-driven system taking the burden off the generators, Beech wasn’t a fan of the horsepower coming off that R/H engine. So, they took the same five-cylinder compressor they were using in the newer 90s and plugged it into the engine-driven A/C systems of the larger King Airs. Fortunately, it took less horsepower off the R/H engine. Unfortunately, it pumped less Freon. The cylinders on the new compressor were much smaller than those on the original six-cylinder unit. So fewer cylinders and smaller cylinders meant less Freon moving around. This made the expansion valves less effective in dropping the air temperature because there’s less volume moving through the system. The result? Less cooling capacity than before.

To review: King Airs with engine-driven A/C have no air conditioning on the ground unless the R/H engine is running. And when the engine is running and the A/C is turned on, it doesn’t cool the cabin very well because of the reduced capacity of the smaller compressor. Plus, the engine is not running at max power on the ground. It’s just like running the A/C in your car while at idle – it blows much more cold once you get on the freeway. In a King Air with engine-driven A/C, it doesn’t really kick in to cold until you are airborne.

The final blow was the switch from R-12 to R-134a refrigerant. That didn’t do King Air air conditioning any favors. Even the motor-driven system is less effective.

The Air is Barely There – A/C in the 350

Anemic A/C is a common complaint with 350 owners. Beech’s 350 added two feet to the cabin of the 200/300 series. I’m guessing this added roughly 30-36 additional cubic feet to be cooled, but they kept the exact same A/C system. The 350 made its debut after Beech switched its engine-driven system to the much smaller five-cylinder compressor, so it’s no big surprise that the A/C in a 350 is a big disappointment.

There is a very expensive factory option for 350s (also available as a very expensive STC) which provides for an electric motor-driven A/C system. It ties in with the existing system to service the whole cabin. It can be used with a GPU to pre-cool a heat-soaked cabin on the ground before boarding passengers. It’s not common and it’s not cheap, but for a 350 it’s very cool … literally.

Maintenance Tip – Find a Good A/C Guy

When your A/C goes out and it’s beastly hot, your desperation level goes up and you may be tempted to go with what you can conveniently get. Frankly, you are better off putting a wet towel around your neck, gritting your teeth and flying home or somewhere that has a proven record with King Air A/C, than to try your luck with a shop you are not sure about. I’m not one to toot my own horn, and I’m not one to bash other shops, but I have seen many attempts to fix air conditioning go horribly awry in the hands of people who don’t know what they are doing. Guesswork doesn’t cut it.

To work on air conditioning, I must be licensed to buy Freon; I need the special gauges, fittings valves and oils that every air conditioning technician must have, and I need them for R-12 as well as R-134a; I need a sniffer for leak detection; I also need expensive machines to evacuate Freon from a system and save it until the system is ready to be serviced. Even though Freon is heavier than air, I mustn’t allow any of it to escape, for fear that it fly 12-19 miles above the earth to assault the ozone layer (but that is a topic for another time and place). Here’s my point: Whoever works on your A/C needs all the equipment needed. They also require a full subscription to the manuals for all King Air models (which aren’t cheap) and an understanding of King Air air conditioning systems, quirks and all.

True story: A King Air 300 that comes to our shop regularly for phase inspections is based in another state. The pilot/manager relies on local sources if there’s a squawk between inspections. He had what he thought was a simple A/C problem and an important flight coming up. He turned to a local shop which assured him they could fix it in a jiffy, but it turned into a nightmare. The pilot called me over and over, apologizing like crazy in his frantic attempt to troubleshoot the problem for the shop and get his King Air back in service. They didn’t even know the proper amount of refrigerant required by that system, the pilot had me look it up for them!

It got worse. After four days, the pilot had to yank his aircraft out of the shop for that important trip (with no A/C in triple digit temperatures). He managed to swing by my shop for a look-see, but he only had a few hours. With three guys we had it diagnosed in about an hour. Using the sniffer, we determined the system was not leaking, but we found other issues. First, it was still a tad low on Freon. Sometimes it’s that last half a pound, or even a few ounces, that makes all the difference. Second, we found the switch that turns the A/C off below 50º F was inoperative. And third, we found the condenser blower was intermittent due to a loose terminal block.

This was good news considering the other shop had seen stains on the condenser and therefore assumed it was leaking Freon. They had no sniffer, so they were shooting in the dark.

Based on guesswork alone, they had recommended the condenser be changed. This is a very expensive part and an extremely labor-intensive job. Although the pilot couldn’t stay for us to fix the problems we identified,
he was thrilled to know exactly what was necessary to get that A/C system blowing cold again. He was even happier to know that their recommendation to change the condenser was completely unnecessary.

Moral

The moral of the story is this: Make darn sure you know what kind of Freon your King Air takes and find out the exact refrigerant capacity of its A/C system. Make a note of this somewhere other than the logbooks, because when your A/C goes out you probably won’t have the logbooks handy.

The most common problem is that the system is a little low on Freon. This does not imply there is a leak somewhere. The maintenance manual states clearly that it is normal for the system to lose a few ounces per year. If you haven’t serviced it in 18-24 months, it could be down just enough to compromise the cooling capability.

If it’s more than just a low-Freon problem, then find someone that has a knack for air conditioning with King Air capabilities and equipment. In a cool King Air cabin, everyone’s happier.