Heating Sequence Of Operation; Ignition Control Led; Adjustments; High Altitude - Mr. Heater MHU 50NG Guide D'utilisation Et Manuel Du Propriétaire

11. If unit does not light first time (gas line not fully purged) it
will attempt up to two more ignitions before locking out.
12. If lockout occurs, repeat steps 1 through 9.
13. If appliance still will not operate, follow the instructions "TO
TURN OFF GAS TO UNIT" and call your service technician or
gas supplier.
HONEYWELL VR8205M GAS VALVE
GAS VALVE KNOB SHOWN
IN OFF POSITION
INLET PRESSURE TAP
MANIFOLD PRESSURE ADJUSTMENT
FIGURE 10
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.
to OFF position.
3. Rotate black knob

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 pre-purge 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,
MANIFOLD
PRESSURE TAP
GAS VALVE
SCREW UNDER CAP
ROTARY SWITCH
Compact Unit / Utility Heater
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 de-energized.

IGNITION CONTROL LED

The ignition control board contains a green LED which indicates
the following:
LED
Slow Flash*
Fast Flash
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
4 Flashes
5 Flashes Flame sensed and gas valve not energized
Steady Off
Steady On
*When thermostat is placed in continuous fan mode LED will slowly flash.
IGNITION CONTROL LED

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.
E-11
Operating Instructions and Owner's Manual
UNIT OPERATION
Normal Operation - No call for heat
Normal Operation - Call for heat
or failed open after CAB is energized
High limit or rollout switch open
Loss of power
Ignition control failure
TABLE 3