Page 14 - Volume 11 Number 8

when I suspected a lot of moisture in a system after repairing a large leak. 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.
An Open System Invites 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 minimum.
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 effectivity of the new receiver-drier.
Confession
I went to air conditioning school when I worked for an automotive shop during high school. In the many years since, I’ve worked on a wide variety of auto and aircraft AC systems but, lucky for me, I’ve never had to deal with Black Death. Yes, I have been working for many years in a desert climate which is less conducive to Black Death than high humidity, but I don’t know if that tells the whole story.
My “partner in crime” for AC troubleshooting and repair hasn’t dealt with Black Death in his long career either. Together we’ve troubleshot and repaired King Air AC systems that others gave up for dead, but none with Black Death.
in the desert, but others lived in coastal environments.
Here’s what I do know: He and I are on the same page regarding pulling vacuum – the more time, the better. When it comes to purging moisture from AC 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 AC squawk, don’t be in a hurry. Consider this typical scenario: Your AC 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 have 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 don’t find any, so they top off the Freon and send you on your way. Most likely your AC will blow ice cubes, but the door was opened for moisture to get into the system and this could hamper AC performance down the road.
If you find your AC blows cold, then warms up, then gets cold again – get your aircraft to a shop. In my experience, this intermittent cooling indicates moisture in the system. AC techs can diagnose this with their gauges. If you’re really pressed for time or far from home base, you can have the AC serviced with Freon as a stop-gap measure. But as soon as you can schedule it, put the aircraft down for a thorough check and fix of the AC. Allow the time.
The Good Guys
Besides patience, you need a shop with a good AC guy. Anyone can throw Freon in a system, but proper servicing and effective troubleshooting requires specialized
If an AC system was left open for a
period of time, for whatever reason,
I would change the receiver-drier.
It contains a desiccant. Receiver- Some of those King Airs lived
12 • KING AIR MAGAZINE
AUGUST 2017