York International ZQ Series Installation Manual page 64

If the call for cooling is still present at the
conclusion of the ASCD, the UCB will re-energize the
compressor.
Should a low-pressure switch open three times
within one hour of operation, the UCB will lock-
out the compressor and flash a code on the ETC or
send error message to the LCD Smart Equipment™
Control.
Freezestat (ETC Only)
During cooling operation, if a freezestat opens, the
UCB will de- energize the compressor, initiate the
ASCD, and stop the condenser fan. If the call for
cooling is still present at the conclusion of the ASCD,
the UCB will re-energize the halted compressor.
Should a freezestat open three times within two
hours of operation, the UCB will lock-out the
associated compressor and flash a code on the ETC.
Evaporator Low Limit (Smart Equipment™
Control Only)
During cooling operation, if the Evaporator Low
Limit Sensor (EC1) (Located on the Suction Line
at the Evaporator Coil.) detects a temperature
below 26°F (default), the UCB will de-energize
the compressor, initiate the ASCD, and stop the
condenser fan. If the call for cooling is still present
at the conclusion of the ASCD, the UCB will re-
energize the halted compressor.
Should the evaporator low limit sensor (EC1) detect
a temperature below 26°F three times within
two hours of operation, the UCB will lock-out the
associated compressor and flash an error message.
Low Ambient Cooling (Smart Equipment™
Control Only)
To determine when to operate in low ambient
mode, the UCB has an Outdoor Air Temperature
Sensor (OAT) with a low ambient setpoint at
45°F (default). When the OAT Sensor senses a
temperature below the low ambient setpoint and
the thermostat is calling for cooling, the UCB will
operate in the low ambient mode.
Low ambient mode operates the compressors in
this manner:
10 minutes on, 5 minutes off. The indoor blower is
operated throughout the cycle. The 5-minute off
period is necessary to defrost the indoor coil.
64 INSTALLATION MANUAL ZQ SERIES 3 - 5 ton 60 Hertz R-410A
Low ambient mode always begins with compressor
operation. Compressor minimum run time may
extend the minutes of compressor operation. The
off cycle will begin immediately following the elapse
of the minimum run time.
When operating in low ambient mode, an
Evaporator Low Limit Sensor (EC1) temperature
below 26oF will de-energize the compressor. If the
call for cooling is still present at the end of the ASCD
and the evaporator temperature (EC1) is above 26°F,
the unit will resume operation
Safety Controls
The Unit Control Boards monitor the following
inputs for each cooling system:
1. For the ETC, a suction line freezestat will
protect against low evaporator temperatures
due to a low airflow or a low return air
temperature (opens at 26 ± 5°F and resets
at 38 ± 5°F). For Smart Equipment™ an
evaporator low limit sensor (EC1) (Located on
the Suction Line at the Evaporator Coil) will
protect against low evaporator temperatures
due to a low airflow or a low return air
temperature, set at 26°F.
2. A high-pressure switch to protect against
excessive discharge pressures due to a
blocked condenser coil or a condenser motor
failure, (opens at 625 ± 25 psig).
3. A low-pressure switch to protect against loss
of refrigerant charge, (opens at 50 ± 5 psig).
The above pressure switches are hard-soldered
to the unit. The refrigeration systems are
independently monitored and controlled. On any
fault, only the associated system will be affected by
any safety/preventive action.
The unit control board monitors the temperature
limit switch of electric heat units and the
temperature limit switch and the gas valve of gas
furnace units.
Compressor Protection
In addition to the external pressure switches, the
compressor also has inherent (internal) protection.
If there is an abnormal temperature rise in a
compressor, the protector will open to shut down
the compressor. The UCB incorporates features to
minimize compressor wear and damage. An Anti-
Short Cycle Delay (ASCD) is utilized to prevent
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