Page 18 - Volume 14 Number 8

Sometimes, pushing the air conditioning reset switch in the nose wheel well is all that is needed to get the air conditioning running again.
If you get the load meter spike in “Auto” or “Manual,” run the engine for 10-12 minutes then shut it down; get out of the cockpit and check the reset switch in the nose wheel well again. If that yellow light is on again you now know your system is tripping on the low-pressure side of the system. You are likely low on Freon. If you never saw a load meter spike then the condenser blower never came on; most likely the blower is bad causing the system to trip on the high-pressure side.
No Yellow Light
The AC reset switch is handy for troubleshooting when it is working, but the yellow lamp inside the switch was not designed to survive in an environment like the nose wheel well, so they tend to burn out easily. As mentioned, if there is no yellow light, press the reset button anyway to see if the AC will come back on. If it does, then that yellow light needs to be replaced. If the AC goes offline after a few minutes, then you have other problems to be addressed that are difficult to troubleshoot in the field.
Reset Switch – Righthand Wing Center Section
In older King Airs (think straight 200s) the AC reset switch is in the righthand center section of the wing inside a six-inch by six-inch panel with three camlock screws. Remove the panel and look in and toward the outboard side where you will see a printed circuit board with two red lights; one is labeled “Low” and the other “High.” If either red light is on, make a note which one it is so you can tell your shop and they will know where to start. You will also see a little red push-button switch which will turn either red light off.
16 • KING AIR MAGAZINE
I miss these reset switches in the wing. It is a simple, straightforward system that saves a lot of time and money searching for the AC system problem. I’m consulting on a 200 right now with this configuration. The AC was inoperative for a of couple of years – there were several problems at play – finally the mess is being unraveled.
50 Degrees Fahrenheit Threshold
Don’t forget that the AC will not turn on if the outside air temp is below 50 degrees Fahrenheit. If you depart a hot climate with everyone in the aircraft melting from the heat, then you land in a cooler climate where a front just passed through and it’s 48 degrees Fahrenheit outside, you’ll have no luck with troubleshooting your AC problem. The OAT needs to be above 50 degrees Fahrenheit.
Summary
Let’s review: Try the AC in “Auto” first; if it doesn’t work, go to “Manual” and toggle the Increase/Decrease switch. If the AC will work in “Manual” then the system itself is fine and the only thing that needs attention is Auto Mode.
If your belt and quill shaft are intact but the AC isn’t working, you may have issues with a pressure switch or the power supply to the PCB.
If your reset switch is working and tells you the system is tripping on the high-pressure side, the shop knows to look at the condenser blower. If the reset switch indicates it is tripping on the low-pressure side, the shop knows to check the Freon level.
If you cannot get an “N1 Low” light without toggling the Increase/Decrease switch, you most likely have a temp sensor issue.
Remember my goal here is to help you jump-start the repair on your air conditioning system. Your technician needs a pilot’s perspective on the problem. The more information you offer about what your system is doing or not doing, the more quickly your shop can zero in on the crux of the matter, saving both time and money.
Stay healthy, fly safely and keep cool. KA
Note: This article was adapted from one in the April 2012 issue. New
King Air owners have requested I revisit some of my earlier topics.
Dean Benedict is a certified A&P, AI with 45 years’ experience in King Air maintenance. He’s the founder and former owner of Honest Air Inc., a “King Air maintenance boutique” (with some Dukes and Barons on the side). In his new venture, BeechMedic LLC, Dean consults with King Air owners and operators on all things King Air related: maintenance, troubleshooting, pre-buys, etc. He can be reached at dr.dean@ beechmedic.com or (702) 773-1800.
AUGUST 2020