Modes Of Operation - McQuay PDAA Installation & Maintenance Data

Modes of Operation

Standard Digital Touchpad Control
Outdoor Air Sensor Reading
To advance from Indoor Coil Sensor reading to
Outdoor Air Sensor reading, press the Mode button
once. The control readout will show the outdoor air
sensor temperature.
Figure 36. Outdoor Air Sensor Location
Outdoor Air Sensor
(OAS)
Thermistor Failure Code and Condition
The system treats a sensor open or short as
extremely cold or hot and reacts accordingly. The
exception is the room air sensor, in which case the
system will turn off. When the fault is corrected by
replacement or repair, the respective error code will
clear from the display (Table 1).
Table 3. – Failure Code and Condition
Thermistor Sensor Condition
Room
Indoor Coil > 176°F for > 2s or
< - 22°F for > 2s or
Outdoor Air > 176°F for > 2s or
Compressor Random Restart
When power is interrupted, a random compressor restart
delay of 0 to 2 minutes is initiated. In the Cool Mode
only, the compressor will start operating only after the
random delay plus 2 minutes (minimum off time for
thermostat 2 to 4 minutes). Random delay is used only
during system startup or reset.
Unit Protective Logic
Compressor Minimum Run Time
For thermostat-controlled running cycles, the
compressor will have a minimum run time of 90
seconds. The compressor can be stopped at any time if
the system is switched to any Mode, except the Cool
Dry Mode.
Error Code
< - 58°F or
> 140°F or
Open or Close
< - 22°F for > 2s or
Open or Close
Open or Close
Compressor Minimum Off Time (delay on
break)
When compressor is under the thermostat control,
it has a 2-minute delay before restarting when it has
cycled off.
Anti-freeze Protection
In Anti-Freeze Mode, the compressor and outdoor
fan will be stopped and the display will show "CF".
The compressor and outdoor fan can be started only if
the following conditions are met:
1. after the 2 minute delay on break, AND
2. the indoor coil reaches 49°F or above and remains
there for at least 1 minute, OR
3. another Mode is selected.
The system is in Anti-Freeze Mode when the
following conditions are met:
1. The control is in either Cool or Cool/Dry Mode.
2. The indoor coil reaches 32°F and stays there for at
least five (5) minutes.
3. The compressor has run for at least 90 seconds.
Sleep Timer is overridden during this operation.
Anti-freeze Protection is active in all modes of
operation and when the control is Off.
Room Freeze Protection
When room temperature falls below 41°F, the
E1
hydronic valve is opened and the indoor fan operates
on High Speed. The compressor and outdoor fan are
off and the display will show "Rf". The hydronic valve
E2
will close when the room temperature rises back to
50°F. During room freeze conditions, the temperature
setting can be adjusted with the touchpad. Fan modes
E4
and Sleep Operation are overridden during Room
Freeze Protection. Room Freeze Protection is active in
all modes of operation and when control is off.
Temperature Limiting
When the room temperature drops 5°F below set
point, the display will indicate "Lo." When the room
temperature rises 5°F above set point, the display
will indicate "hI." Alarm indications of 5°F above or
below set point will be consistent with the set up mode
settings for minimum and maximum temperatures.
IM 934-2 Applied PDAA/PDHA / Page 25 of 44