©2005 McQuay International (800) 432-1342 www.mcquay.com
OM 813 (8-05) / Page 8 of 8
This document contains the most current product information as of this printing. For the most up-to-date product information,
please go to
www.mcquay.com.
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.
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 “AF”. 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 54°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 30°F and stays there for at least
five (5) minutes.
3.
The compressor has run for at least 90 seconds.
Fan Modes, Constant or Cycle, and the Delay On/Off Timer are
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 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 will close when the room temperature
rises back to 50°F. During room freeze conditions, the temperature
setting can be adjusted with the touch pad. Fan modes 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.
Outdoor Air Low Ambient Lockout
If the outdoor air temperature is lower than 40°F, the compressor
and outdoor fan will stop and the display will indicate “LA”.
When outdoor air temperature is 50°F or more, the unit will
resume normal operation.
Table 1. – Failure Code and Condition
Thermistor Sensor
Condition
Error Code
< - 58°F or
Room
> 140°F or
E1
Open or Close
< - 22°F for > 2s or
Indoor Coil
> 176°F for > 2s or
E2
Open or Close
< - 22°F for > 2s or
Outdoor Air
> 176°F for > 2s or
E4
Open or Close
Outdoor Air Sensor Reading
To advance from Indoor Coil Sensor reading to Outdoor Air
Sensor reading, press the Mode button once. The control read-
out will show the outdoor air sensor temperature.
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 (see Table 1, page 8).
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, ie. 2 to 4
minutes). Random delay is used only during system startup or
reset.
