Sunlife Enterprises DM180, DM300, DM240 installation manual Limit Control Setting, Safety Controls

356214-XIM-A-0108

If the temperature limit opens three times within one hour, it will lock-on the indoor blower motor and a flash code is initiated (See Table 24).

GAS VALVE

The UCB continuously monitors the GV. Any time the UCB senses voltage at the GV without a call for heat for a continuous five-minute period, the UCB will lock- on the indoor blower and a flash code is initiated (Table 24). When voltage is no longer sensed at the GV, the UCB will de-energize the indoor blower follow- ing the elapse of the fan off delay for heating.

If voltage has been sensed at the GV for at least 15 seconds during the fan on delay for heating and GV voltage or "W1" is lost, the indoor blower is forced on for the length of the fan off delay for heating.

SAFETY CONTROLS

The unit control board monitors the temperature limit switch and the gas valve of gas furnace units.

The control circuit includes the following safety con- trols:

1.Limit Control (LS).

This control is located inside the heat exchanger compartment and is set to open at the temperature indicated in the Limit Control Setting Table 21. It resets automatically. The limit switch operates when a high temperature condition, caused by inadequate supply air flow occurs, thus shutting down the ignition control and closing the main gas valves and energizing the blower.

2.Centrifugal Switch (CS).

If the draft motor should fail, the centrifugal switch attached to the shaft of the motor prevents the igni- tion controls and gas valves from being energized.

3.Redundant Gas Valve.

There are two separate gas valves in the furnace. Each valve contains a main and a redundant valve.

The redundant valves are located upstream of the main gas valves. Should either or both of the main gas valves fail in the open position the redundant valves serve as back-ups and shut off the flow of gas.

4.Flame Sensor Rod / 100% Ignition Control Lock- Out.

The flame rods and controls are located per Proper Flame Adjustment Figure 22. If an ignition control fails to detect a signal from the flame sensor indi- cating the pilot flame is properly ignited, then the main gas valve will not open. It will continue to try and ignite the pilot for a maximum of 85 seconds, then if the pilot flame is not detected, the ignition control will lock out furnace operation until 24V power is removed from the module either at the unit or by resetting the room thermostat.

5.Rollout Switch.

This switch is located above the main burners in the control compartment, which in the event of a sustained main burner rollout shuts off and locks out both ignition controls closing both gas valves. The ignition controls lock out furnace operation until 24V power is removed from the controls either at the unit or by resetting the room thermostat.

NOTE: The auto reset rollout switch must reset before allowing furnace operation.

6.Auxiliary limit switch (AUX) -

This control is located inside the heat exchanger compartment and is set to open at 190°F. It is a manual reset switch. If AUX trips, then the primary limit has not functioned correctly. Replace the pri- mary limit.

TABLE 21: LIMIT CONTROL SETTING

Units	Capacity, MBH		Limit Control
(Tons)			Opens, ºF
	Input	Output
15, 20 & 25	300	240	195
15, 20 & 25	350	280	195

Johnson Controls Unitary Products 41