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Viessmann AirflowPLUS AH2A Installation, Operating and Service
Control Inputs
Heating control
A 24VAC input is provided to control the heating
function. When the thermostat calls for heat 24VAC
is applied to the W contact and a heating cycle will be
initiated.
Note: the heating cycle control will be ignored while a
cooling cycle is in progress.
If the heating control is turned off during the initial heat
exchanger warm up or during the fan cycle up to speed
the heat mode will be terminated with a short run period
for the fan prior to shutting down.
When thermostat changes off to on:
Initially pump speed is active, Fan is off. Provide time for
heating coil to warm up. After 15 sec. the fan will active at
normal operating speed as set up by the selected dip switch
settings. See setting fan speed pages 32, 33 and 34.
Cooling control
A 24VAC input is provided to control the cooling function.
When the thermostat calls for cooling 24VAC is applied
to the Y contact and a cooling cycle will be initiated.
Note: the heating cycle control will be ignored while a
cooling cycle is in progress.
If the cooling control is turned off during the fan cycle up
to speed period the cool mode will be terminated without
an end of cycle fan period.
Thermostat fan on/auto control
The 24VAC Thermostat Fan On/Auto input will select the
fan operation. When the thermostat is in the Auto state
the fan will be off while not heating/cooling. In the fan ON
position, 24V is applied to the G contact and the fan will
run at the lowest speed while not heating/cooling. During
a heating cycle the fan is always off during the initial heat
exchanger warm up period.
Installation
31
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