Defrosting - Blue Bird Micro Bird Operator's Manual

MICRO - BIRD

DEFROSTING

Windshield fogging and frosting is caused by warm, humid
air coming in contact with a cold windshield which causes the
moisture in the air to condense and possibly freeze if the wind-
shield is cold enough. The warmer the windshield, the less
moisture will condense on it. During initial warm up the defroster
blowers should be operated at maximum to heat the inside of the
windshield glass as much as possible.
If the defrosters are not turned on until the condensation
starts, it is more difficult to heat the glass and overcome condensa-
tion. As passengers are loaded onto the bus, the moisture content
of the air inside the bus increases. The most difficult conditions
will be encountered when there is a large passenger load which
must remain on the bus for extended periods of time, such as on a
charter or over the road activity trip. Travelling at highway road
speeds causes accelerated heat dissipation through the windshield
glass, and each passenger continually adds to the moisture content
of the air within the bus. After a period of time the moisture
concentration can become quite high. This condition can be
improved by slightly opening the forward driver's window, al-
lowing the moist air to escape into the low pressure area outside
the bus at that location and by operating all defroster blowers at
high speed. If bus is equipped with adjustable static air vents in the
roof, they should be kept open, and exhaust fans, if so equipped,
should be used.
Auxiliary fans mounted on the dash or overhead may be
helpful in windshield defrosting when used to force warm air from
inside the body against the glass to warm it and evaporate mois-
ture. They should not be directed to oppose the flow of air from the
defroster outlets but to assist that flow if possible. Many different
variations of auxiliary fan directions have been found to be effec-
tive under different conditions and their use on your unit can
probably best be determined by trial.
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