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Service
Alarm Relay and LED Fault Codes
Control LED flash codes
A visual display is provided by the housing mounted LED.
This display advises of the current status of the air handler
behavior and its environment should unusual conditions
exist. Refer to the chart below. When multiple flash codes
are being displayed, they will be displayed in the following
order:
Flash Code Explanation
RRR
Cooling Lockout
RRG
Freeze protect cycle in process
GRR
A/C Delta exceeded 3 times
RGR
High A/C coil delta
RGG
Low ambient temperature
R = Red
G = Green
Alarm Buzzer
RED LED Sensor
Sounding
Indication
YES
3 flashes
(Freeze Sensor)
YES
4 flashes
(Discharge Air Sensor)
YES
1, 3, 4, 5 or 6
flashes
YES
1, 3, 4, 5 or 6
flashes
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Viessmann AirflowPLUS AH2A Installation, Operating and Service
Alarm
Alarm Relay is on when an unusual condition is detected.
The connector is a two terminal connector that provides
a contact closure when the Alarm Relay is on. The alarm
beeper may be silenced for 24 hr. (if sounding due to a
defective sensor) by turning power to the unit off and
then on. If the condition still exists after 24 hr. the alarm
will be activated again.
Cause
It can be silenced again by turning power to the unit off
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and on. An alarm condition does not mean the unit is
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not working, it just means the information the control is
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receiving does not meet specifications. These conditions
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could be cool supply water, discharge air temperature too
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cold, room air too cold, etc.
The alarm will shut off when the condition is corrected.
Note: There must be 1 sensor on all inputs in the proper
Refer to pages 25 and 26 for detailed sensor information.
Followed
LED
by:
Flash Code
7 green flashes,
then 7 green flashes
7 green flashes,
then 7 green flashes
8 red flashes,
then 8 red flashes
8 red flashes,
then 8 red flashes
Temperature Sensor RED LED Flash Code Identification
1 Flashes Water In Temperature Sensor
3 Flashes Water Coil Freeze Temperature Sensor
4 Flashes Discharge Air Temperature Sensor
5 Flashes Return Air Sensor
6 Flashes Ambient Temperature Sensor
locations. If A/C coil is in the return air plenum then
the return MUST be installed on the board at the
RETURN AIR receptacle with the sensor lead
end located 15" (381 mm) upstream of the A/C
coil in the return air duct.
The discharge air sensor (supplied) shall be
installed downstream of the heating coil in
the supply air ductwork and attached to the
DISCHARGE AIR receptacle location on the
control.
Reason
Water coil Freeze Sensor temperature or
Discharge Air Sensor limit exceeded –
inadequate air flow, A/C locked on.
Water coil Freeze Sensor temperature or
Discharge Air Sensor limit exceeded –
inadequate air flow, A/C locked on.
Temperature Sensor misread,
wait for next indication.
Failed Temperature Sensor.
Replace.
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