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Viessmann AirflowPLUS AH2A Installation, Operating and Service
Illuminated Alarm Indicator
Legend
A Ambient air temperature sensor
B Indicator light
Audible Alarm Indicator
Enabled
Immediately
After 24 h
After 10 min
Sound
4 beeps
A/C locked out after three successive freeze protect cycles
2 beeps
1 beep
• All Viessmann AirflowPLUS AH2A series air handlers
are equipped with a housing mounted Illuminated alarm
indicator. This indicator light illuminates any time the
control mounted alarm relay is activated.
• The control mounted alarm relay is turned on under
the following circumstances.
1) Home freeze protect
Automatic Home Freeze Protection is initiated when the
ambient air temperature reads lower than 40°F (4°C).
During this time the alarm relay and heat cycle are turned
on until the ambient temperature rises above 54°F (12°C).
2) Heat exchanger freezing protection control.
The system is protected from damage that may occur due
to freezing during an A/C cycle. The system will enter a
freeze protect cycle under the conditions described below.
During the freeze protect cycle the fan and pump will run
at high speed and the A/C relay will turn off. The system
will run in this state for five minutes and then return to
normal operation. While the unit is in freezing protection
mode, the alarm relay will be activated.
If the freeze protection sensor is below limit freeze
protection is initiated. The limit is 57°F (14°C) for
systems with the evaporator in the supply air stream,
and 43°F (6°C) for systems with the evaporator in the
return air stream. Freeze protect is also initiated when
the discharge air temperature is less than 41°F (5°C) ,
the unit will go into freeze protection mode.
3) Cooling lockout
If the A/C coil Freeze Protect Cycle (2 above) is
initiated three times within the same cooling cycle,
the system goes into Cooling Lockout Mode. During
this time the cooling cycle is disabled and new cooling
cycles are blocked. The cooling cycle can only be
reintroduced by cycling the power to the air handler,
off and on. During this lockout mode the air handler
control audible alarm will also sound.
4) Temperature sensor failure
If a sensor has a bad read, or is malfunctioning, the LED
will blink RED 8X-8X rather than the green temperature
reading. This 8X blink may repeat. Be sure to cycle
through all sensors at least three times to determine is
a sensor is faulty.
Certain error conditions enable a beep code output. The
beep code repeats every 8 min. after it is enabled. Some
conditions have the beep enabled immediately, others are
not enabled until the unit has been on for at least 24 hours.
This allows the beeping to be cancelled by cycling power.
For service, note the beep condition before cycling power.
Error
One or more bad temperature sensors
low ambient temperature
Service
41
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