Component Description And Operation - PHP Heat Wagon LVF90A Service Manual

Indirect Heater Component Description
and Operation
Most indirect heaters are high pressure and therefore share most of their com-
ponents with the high pressure heaters. Please read the "High Pressure Oil
Component and Description" section on pages 100-102 if you are not already
familiar with high pressure oil components. The following components are
found only on indirect oil heaters.
Control Board
The control board functions as the "brain" of the indirect oil heater and
determines if and when the motor, transformer and fuel solenoid valve
receive power. Some control boards receive power from the power cord thru a
thermostat. Other control boards are wired to a thermostat "socket" which
contains either a "jumper cap" for continuous running or a thermostat
plugged into the socket for thermostatically controlled operation. The control
board also is connected to a flame sensing photocell. This allows the control
board to run the heater when combustion is established and shut the heater
off if flame is not present. The control board may also be wired to an air
proving switch. Air from the turning fan blade must close this switch for the
heater to ignite or run. Some heaters have a overheat or limit switch wired to
the control board to shut the heater off if it overheats.
Heat exchanger
The heat exchanger allows heat in the combustion chamber to transfer into
the exchanger. The open flame in the combustion chamber never touches the
heated output air. This keeps the products of combustion and moisture creat-
ed by the flame separate from the clean, dry output air.
Air Damper
The air damper or air shutter setting controls how much air enters the com-
bustion chamber. The correct amount of air is vital for ignition and combus-
tion. Follow the manufacturer's specifications when setting or adjusting the
air damper.
Thermostat / Jumper Cap
Most indirect heaters have a standard or optional thermostat. The thermostat
may be wired in between the power cord and the control board or may have a
"socket" for attaching a remote thermostat. The "socket" must have a "jumper
cap" in place if the remote thermostat is not used or the heater will not oper-
ate. The thermostat functions as an on/off switch to cycle the heater to main-
tain a desired temperature.
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