Fan Control Circuit - AGFA Avantra 36/44 Service Manual

Avantra 36/44 Service Manual
2.15.3.1 Power
The fan power connector (J3) located on the right door supplies the +24 volts used
on the board.
NOTE:
The door fan is not required when the system has a humid-
ifier installed.
The (J3) connector supplies power to the wiring harness, which in turn supplies
power to the humidifier electronics module. Power from (J3) is in series with the
door interlock switches. Power to the humidifier shuts off when either end cap is
opened.
The +24 volt power from the engine connects to the electronics module through
the (J2) connector. Power feeds through the U3 voltage regulator to generate a +12
volt source for the board.
LED CR3 acts as a visual U3 output indicator. The +24 volt power also feeds
through relay K1, which controls power to the fan and water valve solenoid cir-
cuits. A software function exists for turning off the K1 relay and thus disabling the
fan and solenoid functions. LED CR1 acts as a visual indicator for the switched +24
volts.
2.15.3.2 Float Switch and Water Valve Solenoid
The float switch and water solenoid, which are part of the humidifier assembly,
connect to the electronics module through connector (J2). The switch and solenoid
represent a closed circuit with the float switch directly controlling the water sole-
noid valve.
When the water reservoir is full, the normal switch condition is closed. A closed
switch turns off transistor Q1, which in turn de-energizes the water valve solenoid.
When the water level in the humidifier reservoir drops below a preset level, the
float switch opens, which signals resistor R10 to turn on Q1. This energizes the
water valve solenoid, which opens the valve to fill the reservoir. When the water
reaches the correct level, the float switch closes turning off the solenoid and halting
the water flow.

2.15.4 Fan Control Circuit

The fan control circuit varies the fan speed in response to the drum's humidity
level. When the level falls below 45%, the system turns the fan on at 100% drive
level. When the level reaches 45%, the fan drive circuit reduces the fan speed.
Speed continues to be reduced until a humidity level of 50% is achieved. Further
humidity drops activate the fan and repeat the cycle.
The humidity sensing circuit consists of two sections in series:
• LM339 voltage comparator
• Humidity sensor
2-36 Functional Analysis