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electric heat switch from the top, “Grd Max” position down to the center, “Normal” position. Doing so kills the extra four heat grids and allows the normal four grids to continue to be available ... operating if manual heat is selected and standing by to operate as needed if in the auto mode.
It is rare that electric heat is needed when flying since bleed air heat should be sufficient. However, there are a couple of situations in which in-flight use of electric heat is desirable. The first of these is caused by a very weak or totally dead flow pack. One pack alone should be able to provide full pressurization, but with cold OATs at altitude a single pack won’t provide enough heat to keep the cabin at a comfortable temperature. So, when the cabin is chilly, even with the cabin temperature rheostat cranked up fully clockwise, make sure the electric heat switch is in the center, “Norm” position and turn off the lock-out items. Now the four normal heat grids can come on to add to the total heating capacity.
“But what if I am flying in clouds and need to keep all of the ice protection activated, including the lock-out items?” In that case, hand out the blankets; the cabin will remain chilly.
The second situation in which supplemental electric heat is desirable in flight occurs when engine power remains low for a lengthy period. The lower the power, the less the compressor speed, the cooler the bleed air. During a prolonged low-power descent or while drilling holes in the cold sky in a holding pattern, let the normal heat grids help in keeping the cabin comfortable. As discussed above, you must be out of icing conditions so that the lock-out items may be turned off.
Now addressing the supplemental electric heat system on the 300-series (300s and 350s) and the later 200-series, those produced in 1993 and after. (This discussion does not apply to the Keith Environmental Control System found on 200s and 350s since about 2006.) Instead of normal and ground maximum heating grids, there are two separate heaters installed in the floor air distribution ductwork – one forward and one aft. On the ground, a solenoid latches the electric heat switch in the up, on position when that position is selected while the rotary mode selector is either in the “Auto” or “Man Heat” mode. At this time, only the forward heat grid begins to operate. But in 100% of the cases, you will probably also want the aft heater to operate. By merely moving the aft blower switch to the up, on position, you have achieved that. The heater would get too hot rapidly were there not sufficient airflow over it, so only when the aft blower is running will the aft heater start to operate. Ah, I feel the cabin getting warmer quickly!
The engines installed on the 200- and 300-series have a higher compression ratio than those engines on the smaller King Airs and, because of that, they put out hotter bleed air in flight at typical power settings. Recognizing this, the designers concluded that there would never be a need for supplemental electric heat in
24 • KING AIR MAGAZINE
NOVEMBER 2023