After a long, hot summer, cooler temperatures have finally arrived. You might think the air conditioning system (AC) in your King Air deserves a vacation after all of its hard work in the blazing heat. But before you send your AC into hibernation for the winter, I’ve got a surprising tip that could pay off down the line – run your AC from time to time, even when you don’t need it.
Every year, as soon as the weather warms up, I am besieged with questions from pilots, owners and mechanics about their King Air air conditioning. Sometimes it’s lackluster performance, other times it is completely inoperable (inop).
There are many things that can go wrong with the AC, but let’s consider the most common problems. One being leaky seals that have allowed the Freon to escape, seized expansion valves is another, as well as failed condenser blowers. These are my top three culprits that cause problems with King Air air conditioning. Coincidentally, all three can be aggravated by non-use during the winter and would benefit from periodic running of the AC whenever the OAT is above 50°F. Doing this helps prevent the seals from drying out and becoming brittle, it lubricates the expansion valves and the compressor, and it keeps the greases inside the condenser blower from desiccating.
It’s important to note that you shouldn’t just turn on the vent blower; you need to run the whole system. Five or ten minutes ought to do it. For example, if the OAT is in range, you could run the AC during taxi out. Select Auto Cool and turn the rheostat counter-clockwise all the way. Keep an eye on your load meter. After 7-15 seconds, you should see a marked increase if you’re in a 200, 300 or 350 model series. In a 90, it will spike right away, indicating the air conditioning is on.
If the AC doesn’t come on, it could be that your cabin temp sensor is out of adjustment. In this case, select Manual Cool to bypass the cabin temp sensor and get the AC going. Then make note to put the cabin temp sensor on your list of possible squawks to be checked out at the next inspection.
In general, airplanes do not like to sit idle. I’ve seen it over and over throughout my career, when an airplane is grounded for a long time, things will just break spontaneously. The same is true for systems like the air conditioning.
Remember, it is futile to run the air conditioning when the outside air temp is below 50°F, as the system will not operate. But if the OAT allows, give your AC a little exercise whenever you get the chance. Come next summer, you’ll be happy you made the extra effort.