In most installations the factory settings provide an adequate range of indoor airflow whilst avoiding
risk of indoor coil frost, water carry-over and excessive noise. Care must be taken when changing the
indoor fan speed control voltages:
• To ensure the indoor fan always starts it is recommended to avoid ‘low speed voltage’ settings
below 2V.
• To avoid increased risk of frost protection trips and unit lock-out do not set the fan low speed
so low that the evaporating temperature can fall below 0°C.
• To avoid risk of water leaking from the supply air vents and corrosion of ducting do not set the
fan high speed so high that moisture that may have condensed on the fins of the indoor coil is
blown off the coil and into the supply air duct.
• Reducing the high fan speed settings may help when there’s significant noise from supply air
vents.
• To reduce risk of ‘over-condensing’ during heating mode, which in turn may cause supply air to
feel relatively cool, or even water freeze protection trips, avoid very high fan speed settings.
8.2. Translation from 0-10V fan control input signal VF to a fan output signal
Input VF on the UC8 can be used for a 0-10V control signal for the indoor fan.
If the indoor fan speed is controlled using a control voltage applied to input VF then that input voltage
is translated to a corresponding output voltage. The translation ensures that the UC8 programmed
fan speed settings are obeyed.
Translation from 0-10V input VF to a voltage on output V2 is as follows, assuming the default settings
of 5V for low speed to 8V for high speed.
Input VF Output V2 Fan
0.0V to 0.99V 0V Off
1.0V to 1.49V 0 or 5V Off or Low speed, whichever is currently the case
1.5V to 9.50V 5V to 8V Low speed to High speed
9.5V to 10.0V 8V High speed
If above translation is undesirable then one could follow the procedure described above to change
the minimum and maximum voltage settings, or one could bypass the UC8 and apply the external
control voltage directly to the indoor fan.
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