Page 21 - Volume 14 Number 9

Time to select Man Cool and let the air conditioning come on.
When you move the mode selector to Man Cool it’s a good idea to watch the load meters. You hope to observe a very major electrical load increase since the compressor motor pulls nearly 150 amps. Ah ... here comes the cool air out of the vents! It is unlikely, but possible, that the cabin will actually get a bit too cold. If so, hold the Man Temp switch up to the Incr position for a few seconds to warm up the incoming bleed air. As you continue the descent to your landing it will be typical to again hold the Man Temp switch to Decr until you know the bleed air is as cool as possible.
I often teach that there are actually three, not two, modes of Manual temperature control. The first one is using Man Cool to run the AC continually but with manual regulation of bleed air temperature. The second one is using Man Heat to run the normal electric heat grids continually but with manual regulation of bleed air temperature. The third one – and the one that will likely be used the most – is using Man Heat to allow manual regulation of bleed air temperature but with the Electric Heat switch in the Off position so that no heater grids may operate. Of course, having any of the lockout items on accomplishes the same thing as moving the Electric Heat switch to the Off position.
I will close by discussing the differences in the 200- and 300-series. (Realize that the B300s [350s] after serial number FL-500 have a totally new and different environmental system: The “Keith” system. Our discussion does not apply to them.) The manual control of bleed air temperature via the Man Temp switch stays the same: 30 seconds per side to go from one temperature extreme to the other; left side heats first, right side follows; right side cools first, left side follows. There is no electric heater in the first 1,400-plus of the BB-series except for the puny radiant heat panels in the cabin ceiling. These play no role in either
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the Auto or Man Heat modes of operation. They have their own On-Off switch that functions without any tie-in to any other environmental control. When grid heaters in the forward and aft underfloor environmental ducting replaced the radiant heat panels in 1993 – and which all 300s and the earlier 350s have – they were designed to be a ground use item only. They do not operate in flight since bleed air should always be sufficient to supply the desired heat. (But not when a flow pack is dead!)
There is a significant difference when it comes to Man Cool: The AC system only gets a command to operate when the left Bypass Valve is at or very near the full cold position. This seems to make sense – why engage the compressor clutch, start pumping Freon, and add workload to the right engine until the bleed air is cold? Yet the 90- and 100-series, as we have discussed, allow for AC being on even with full hot bleed air coming in! To recap, in most situations in the 200- and 300-series there is no difference between Man Cool and Man Heat ... they both provide manual control of bleed air temperature via the Man Temp switch. You only add in AC when in Man Cool and the Man Temp switch has been held to DECR long enough to send the bypass valves fully cold.
I hope this review has given you a good reminder of how the Manual modes operate and some tips that will prove to be worthwhile when and if you must revert to their use. KA
King Air expert Tom Clements has been flying and instructing in King Airs for over 46 years and is the author of “The King Air Book” and “The King Air Book II.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his books, contact Tom direct at twcaz@msn.com. Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at editor@blonigen.net.
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