Enerco MHU 45, MHU 75 owner manual Adjustments

ROBERTSHAW 2000DER GAS VALVE

GAS VALVE KNOB SHOWN	MANIFOLD
IN OFF POSITION	PRESSURE TAP

INLET PRESSURE TAP

MANIFOLD PRESSURE ADJUSTMENT

SCREW UNDER CAP

FIGURE 10

13.If appliance still will not operate, follow the instructions “TO TURN OFF GAS TO UNIT” and call your service technician or gas supplier.

TO TURN OFF GAS TO UNIT

1.Set thermostat to lowest level.

2.Turn off all electrical power to unit if service is to be performed.

3.Depress knob on gas valve; knob will snap to OFF.

HEATING SEQUENCE OF OPERATION

1.When the thermostat calls for heat, the combustion air blower starts immediately.

2.Combustion air pressure switch proves blower operation before allowing power to the ignition controller. This switch is factory set and no adjustment is necessary.

3.After prepurge of approximately 30 seconds, the spark ignition is energized and the solenoid valves open in the gas valve.

4.The spark then ignites the gas, the ignition sensor proves the flame and the combustion process continues.

5.In the event that the flame is not detected after the first 10- second trial for ignition, the controller will repeat steps 3 and 4 an additional two times before locking out the gas valve.

Ignition control will then automatically repeat steps 3, 4, and 5 after 60 minutes.

To interrupt the 60-minute lockout period, move thermostat from “Heat” to “OFF” then back to “HEAT.” Heating sequence then restarts at step 1.

6.The burners shall light without noticeable crossover delay. There shall be no flame lifting from the burner heads, flashback or burning within the burner. The flames shall be predominantly blue in color and shall be approximately centered in the tubes with no apparent impingement taking place.

7.The ignition control will energize the fan approximately 45 seconds after ignition is established.

8.After the thermostat demand is satisfied the gas valve is closed; 5 seconds after the demand is satisfied the combustion air blower is shut off.

9.The control center shall shut off the system fan approximately 150 seconds after the gas valve is denergized.

IGNITION CONTROL LED

The ignition control board contains a green LED which indicates the following:

	TABLE 3
	IGNITION CONTROL LED
LED	UNIT OPERATION
Slow Flash*	Normal Operation - No call for heat
Fast Flash	Normal Operation - Call for heat
	Current signal at FLAME terminal 0.6 to 1.0 microamps
2 Flashes	System lockout - failed to detect or sustain flame
	Current signal at FLAME terminal <0.6 microamps
3 Flashes	Pressure switch failed closed before CAB is energized
	or failed open after CAB is energized
4 Flashes	High limit or rollout switch open
5 Flashes	Flame sensed and gas valve not energized
Steady Off	Loss of power
Steady On	Ignition control failure

*When thermostat is placed in continuous fan mode LED will slowly flash.

GAS CONVERSION KIT OPTIONAL

Can be purchased at any Enerco / Mr. Heater dealer or direct from the factory under the following numbers

45NG--	TO--	LP-----	60067	75NG--	TO--	LP-----	60069
45LP---	TO--	NG-----	60066	75LP---	TO--	NG-----	60071

ADJUSTMENTS

HIGH ALTITUDE

Units may be fired at full input up to 2000 ft. (610m) above sea level. Above 2000 ft. (610m), manifold pressure must be adjusted on some units. Adjust pressure regulator to pressure shown in table 4 for natural gas and table 5 for LP/propane gas.

GAS FLOW

To check for proper gas flow to the combustion chamber, determine the Btu input from the appliance rating plate. Divide this input rating by the Btu per cubic feet of available gas. Result is the required number of cubic feet per hour. Determine the flow of gas through the gas meter for two minutes and multiply by 30 to get the hourly flow of gas.

GAS PRESSURE

1.Check gas line pressure with unit firing at maximum rate. A

Enerco Compact Unit Heater 11 Operating Instructions and Owner’s Manual