ing is still present at the conclusion of the ASCD, the UCB will
Should a freezestat open three times within two hours of operation, the UCB will
LOW AMBIENT COOLING
To determine when to operate in low ambient mode, the UCB has a pair of terminals connected to a temper-
Low ambient mode operates the compressors in this manner: 10 minutes on, 5 minutes off. The indoor blower is operated throughout the cycle. The
Low ambient mode always begins with compressor operation. Compressor minimum run time may extend the minutes of compressor operation. The defrost cycle will begin immediately following the elapse of the mini- mum run time.
When operating in low ambient mode, the UCB will not lockout the compressor due to a freezestat trip. How- ever, a freezestat trip will
SAFETY CONTROLS
The unit control board monitors the following inputs for the cooling system:
1.A suction line freezestat to 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).
2.A
3.A
The above pressure switches are
trolled. On any fault, the system will be affected by any safety/preventive action.
The unit control board monitors the temperature limit switch of the electric heat.
COMPRESSOR PROTECTION
The compressor also has inherent (internal) protection. If there is an abnormal temperature rise in a compres- sor, the protector will open to shut down the compres- sor. The UCB incorporates features to minimize compressor wear and damage. An
The ASCD is initiated on unit
FLASH CODES
The UCB will initiate a flash code associated with errors within the system. Refer to UNIT CONTROL BOARD FLASH CODES Table 32.
RESET
Remove the call for cooling, by raising thermostat set- ting higher than the conditioned space temperature. This resets any pressure or freezestat flash codes.
HEATING SEQUENCE OF OPERATIONS
WITH OR WITHOUT ELECTRIC HEAT
When the thermostat calls for the first stage of heating, the low voltage control circuit is completed between “R” and “W1”. The 24vac signal is passed through the UCB to the “Y” contact on the Defrost Control (DC) assuring the reversing valve cannot be energized, except during defrost. If the ASCD timer is satisfied the UCB will energize compressor contactor M1.
If the compressor alone cannot satisfy the heating requirements, a second stage call from the thermostat completes the circuit between “R” and “W2”. This 24vac signal is passed through the UCB to the electric heat section (if available). The total available kW of electric heat will be energized on a call for “W2”.
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