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as on a charter or over-the-road activity trip. Each passenger continually adds to the moisture content of the
air, and after a period of time, the humidity can become quite high. This condition can be improved by
slightly opening the forward driver’s window, allowing the moist air to escape into the low pressure area
outside the bus at that location.
1. Open roof hatch in rear “pop-up” position to flow air through the bus, or
2. Operate the optional roof vent fan at high speed until windows clear and then reduce speed to an
acceptable level.
3. With all heater fans on “hi,” put A/C fan on “low” and point bottom duct diffusers at window (close
off side facing diffusers). Put A/C temperature control on “cool” so that warm air, as it rises, will be
picked up and directed at windows. Note: If frosting of window has occurred (as in very cold cli-
mates), it will be necessary to have the interior reach a temperature high enough to melt the frost
before defogging can begin.
4. Operate the main heater with the fresh air vent in the maximum opened position.
5. Heater booster pump “on.”
6. Heater water flow valve in maximum “red”—turn counterclockwise
Note:
If possible, have the interior warmed before passengers board in very cold conditions.
HEATER DEFROSTER LOCATION
The blower in the front main heater contributes to keeping the driver’s area glass clear of fog and frost.
See OUTLET LOCATION diagram. Defrosting performance is enhanced greatly by the use of fresh air into
the heater. Open front access panel and observe fresh air intake on driver's side of bus to verify the proper
functioning of the fresh air intake.
Satisfactory performance of the body heaters is basically dependent upon:
1. Adequate engine (coolant) temperature—this can be altered by thermostat rating, which should never
be higher than recommended by the engine manufacturer and/or shutters.
2. Adequate coolant flow—this varies with engine speed and can be increased if necessary by the use of
an auxiliary water pump. The heaters are rated at six gallons per minute.
3. Proper fan operation—the three speed motor can most easily be checked for function by operating the
motor switch and listening for the speed variations.
Many other factors affect performance, but the three mentioned are most basic.
DRIVER/PASSENGER COMFORT
When defrosting requirements have been satisfied, the other openings can be set as necessary for comfort.
The adjustable outlets on the rear surface of the dash can be directed toward the driver and/or passengers as
desired. The auxiliary unit under the driver’s seat has a two-speed electrical switch and it directs air upward
for the driver’s left side and forward around the steering column area.
HEATER BLEEDING INSTRUCTIONS
Use of antifreeze (ethylene glycol type only) is recommended for summer or winter operation because of
its corrosion inhibition and lubrication properties. A 50-50 solution of antifreeze and water is preferred and it
gives freeze protection to about 30 degrees F below zero. Ultimate protection is attained at 68% antifreeze
(about 92 degrees F below zero); a higher concentration of antifreeze should never be used.
If it becomes necessary to completely refill the chassis coolant system, the following procedure must be
followed to ensure adequate heater bleeding. During the bleeding process, it will be necessary to remove the
radiator cap and refill cooling system several times to ensure adequate coolant is available to replace purged
air and coolant lost when bleeding.
