Johnson Controls BQ 060, BQ 036, BQ 048 Safety Controls, Compressor Protection, Flash Codes, Reset

364985-XIM-B-0508

ing is still present at the conclusion of the ASCD, the UCB will re-energize the compressor.

Should a freezestat open three times within two hours of operation, the UCB will lock-out the compressor and flash a code (see Table 32).

LOW AMBIENT COOLING

To determine when to operate in low ambient mode, the UCB has a pair of terminals connected to a temper- ature-activated switch set at 45ºF. When the low ambi- ent switch is closed 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.

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 de-energize the compressor. If the call for cooling is still present at the end of the ASCD and the freezestat has closed, the unit will resume operation.

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 high-pressure switch to protect against exces- sive discharge pressures due to a blocked con- denser coil or a condenser motor failure, (opens at 380 ± 10 psig and resets at 300 ± 10 psig).

3.A low-pressure switch to protect against loss of refrigerant charge, (opens at 7 ± 3 psig and resets at 22 ± 5 psig).

The above pressure switches are hard-soldered to the unit. The refrigeration system is monitored and con-

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 anti-short cycle delay (ASCD) is utilized to prevent operation of a com- pressor too soon after its previous run. Additionally, a minimum run time is imposed any time a compressor is energized.

The ASCD is initiated on unit start-up and on any com- pressor reset or lock-out.

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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