Overhead Compartment Unit; Heating; Driver's Unit Hot Water Pneumatic Valve; Passenger's Unit Hot Water Pneumatic Valve - PREVOST H3-41 Maintenance Manual

dehumidification.
6.3.2

Overhead Compartment Unit

Optional A/C evaporator coils may be added to
both overhead compartment air systems. This
air conditioning unit permits a wider temperature
range in the passenger's area.
6.4

HEATING

The schematic of FIGURE 3 shows the central
HVAC system heating arrangement.
On coaches, in addition to the normal heating
provided by the engine, an optional preheating
system (104,000 Btu/hr) may have been
installed above the rear wheelhousing on the
L.H. side.
6.4.1 Driver's Unit Hot Water Pneumatic
Valve
The flow of hot water to the driver's unit heater
core is controlled by a normally-open (NO)
pneumatic valve like. The valve, located at the
ceiling of the spare
(Figure 71), is designed so that the pilot solenoid
valve, which is part of the assembly, opens and
closes a port which directs air pressure to the
actuator casing, thereby opening or closing the
valve.
When the vehicle is operating without electrical
supply to the pilot solenoid valve, no air
pressure is admitted to the actuator casing, the
cylinder spring pushes up against the cylinder,
thereby keeping the water valve open.
Air pressure at port + 24-V signal at coil =
valve closed
The driver's unit hot water valve requires a
minimum amount of maintenance. The valve
should be free of dirt sediment that might
interfere with its
maintenance is needed unless a malfunction
occurs.
wheel compartment
operation. No other
PA1621 Maintenance Manual All Series | Revised February 2019
SECTION 22: HEATING AND AIR CONDITIONING
FIGURE 71: DRIVER'S UNIT HOT WATER PNEUMATIC
VALVE ASSEMBLY
6.4.2 Passenger's Unit Hot Water Pneumatic
Valve
The flow of hot water to the vehicle's central
heater core is controlled by a normally-open NO
3-way pneumatic water valve assembly (Figure
72). The valve, located in the evaporator
compartment, is designed so that the pilot
solenoid valve, which is part of the assembly,
opens and closes a port which directs air
pressure to the actuator casing, thereby opening
or closing the valve.
When the vehicle is operating without electrical
power to the pilot solenoid valve, no air pressure
is admitted to the actuator casing, the cylinder
spring pushes up against the cylinder, thereby
keeping the water valve open.
FIGURE 72: PASSENGER'S UNIT PNEUMATIC HOT
WATER VALVE ASSEMBLY
6.4.3

Draining Heating System

To drain the entire system, refer to SECTION 05
COOLING SYSTEM.
heater core or passenger's unit heater core must
be drained, refer to the following instructions.
22240
If only the driver's unit
57