Sunlife Enterprises DM180, DM300, DM240 Safety Controls, Compressor Protection, Flash Codes, Reset

356214-XIM-A-0108

Should a freezestat open three times within two hours of operation, the UCB will lock-out the associated com- pressor and flash a code (Table 24). If the other com- pressor is inactive, the condenser fans will be de- energized.

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 30ºF. 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 compressors due to a freezestat trip. How- ever, a freezestat trip will de-energize the associated 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 each 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 22 ± 5 psig and resets at 45 ± 5 psig).

The above pressure switches are hard-soldered to the unit. The refrigeration systems are independently mon- itored and controlled. On any fault, only the associated system will be affected by any safety/preventive action.

The other refrigerant system will continue in operation unless it is affected by the fault as well.

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

The compressors also have inherent (internal) protec- tion. If there is an abnormal temperature rise in a com- pressor, the protector will open to shut down the compressor. The UCB incorporates features to mini- mize compressor wear and damage. An anti-short cycle delay (ASCD) is utilized to prevent operation of a compressor too soon after its previous run. Addition- ally, a minimum run time is imposed any time a com- pressor 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 24.

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.

ELECTRIC HEATING SEQUENCE OF OPERATIONS

The following sequence describes the operation of the electric heat section.

Single-stage heating (applies only to 18 KW heater, all other heaters MUST use a two-stage thermostat):

a.Upon a call for heat by the thermostat, the heater contactor (6M) will be energized. After completing the specified fan on delay for heating, the UCB will energize the blower motor.

b.The thermostat will cycle the electric heat to satisfy the heating requirements of the conditioned space.

Two-stage heating (applies to all heaters except 18 KW):

a.Upon a call for first-stage heat by the thermostat, the heater contactor (6M) (6M & 7M on 72 KW, 240V) will be energized. After completing the specified fan

38 Johnson Controls Unitary Products