Nordyne M3RL Series installation instructions Cooling Mode, Fan Mode, Furnace Fails to Operate

Initial Power up: After 30 seconds of igniter warm-up the gas valve (24 VAC) will then open. The igniter circuit will stay ener- gized for 3 seconds after the gas valve opens.

After Initial Power up: The control has a programmed adaptive ignition feature which varies the warm-up period as fol- lows: If ignition is successful the warm-up is reduced by 3-seconds on each subsequent call for heat until ignition failure occurs. Upon ignition failure, the warm-up is in- creased by 3-seconds on the next try. If successful, the timing remains fixed at this level. In general, whenever ignition failure occurs the warm-up interval is increased by 3-seconds on the next try. And if success- ful, it remains there. Minimum and maxi- mum warm-up time limits are set at 6 and 54-seconds, respectively.

7.The furnace control must prove flame via the flame sensor 5 seconds after the gas valve opens. If flame is sensed, all burn- ers are on and the ignitor cools off. If no flame is sensed, the gas valve closes immediately and the inducer continues to run. A second trial for ignition (step 6) begins if no flame is sensed. On the fifth try for ignition, the furnace control is locked out and the red LED will blink 4 times repetitively. The thermostat must be opened for at least ten seconds to reset the furnace control after a lock out. Oth- erwise, the furnace will attempt another ignition sequence in 1 hour.

8.The furnace control energizes the cir- culating air blower on the heating speed 30 seconds after the gas valve circuit is energized .

9.When the thermostat has been satisfied,

gas valve is de-energized.

10.The inducer is de-energized after a 30- second postpurge.

11.The furnace control keeps the circulating air blower energized for 120 seconds (factory set) or 60, 90, or 180 seconds (field adjustable). (See Figure 27.)

12.Abnormal conditions: If a limit opens during operation, the inducer and circulating air blower continue to operate. The gas valve is de-energized immediately. The blowers continue to operate until the limit closes. When the limit closes the inducer blower is de-energized immediately. The circulating air blower continues to operate for the speci- fied delay (factory set at 120 seconds).

Cooling Mode:

1.On a call for cooling the thermostat closes, applying 24 VAC to the G and Y terminals on the furnace control. This closes the compressor contactor.

2.The furnace control energizes the circu- lating blower (115 VAC) on the cooling speed.

3.When the thermostat is satisfied, the G and Y terminals on the control board are de-energized opening the compressor contactor.

4.The circulating air blower is de-energized after a 90-second delay.

Fan Mode:

1.On a call for fan operation, the thermostat applies 24 VAC to the G terminal on the furnace control board.

2.The circulating air blower is energized immediately on the heating speed.

3.If the furnace is operated in the continu- ous ON position at the thermostat and is then switched to AUTO, the circulating blower will operate for a specified delay (factory set at 120 seconds).

Furnace Fails to Operate

If the furnace does not operate check the following:

1.Is the thermostat operating properly?

2.Is the front door in place?

3.Is the furnace disconnect closed?

4.Has the circuit breaker tripped or the control board fuse burned open?

5.Is the gas turned on?

6.Are any manual reset switches open?

7.Is the filter dirty or plugged?

8.Is the flame sensor coated? (Remove and clean with emery cloth.)

9.Is the deck switch open?

If the furnace locks out after 5 attempts for ignition, it will try again every hour if a call for heat remains. If the inducer and circulating air blowers are operating, and items 1 through 8 have been checked, press the red reset but- ton on the vent safety switch. (See Figure 29.) If the furnace operates after depressing the reset button, contact a qualified service tech- nician to identify and repair the problem.

If furnace still fails to operate, depress the red reset buttons on the flame roll-out switch. If the furnace operates after depressing the reset button, contact a qualified service tech- nician to identify and repair the problem.

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