Heating Sequence Of Operation; Ignition Control Led; Adjustments - Mr. Heater MHU 50 Operating Instructions And Owner's Manual

lights burner. DO NOT attempt to light the burners manually.
5. There is a black rotary switch knob that can be moved
between the on and off position. Rotate the switch knob to
the off position. (See Figure 10)
6. Wait five minutes to clear out any gas. If you then smell gas,
STOP! Immediately call your gas supplier from a neighbor's
phone. Follow the gas supplier's instructions. If you do not
smell gas go to next step.
7. Rotate the black switch knob to ON.
8. Turn on electrical power to unit.
9. Set the thermostat to desired setting.
10. The combustion air blower will start. The burners will light
within 30 seconds.
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.
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 valve opens 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. Refer
to ignition control board table 3. 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. If your burner characteristics do not match those
described above. Refer to the trouble shooting sections.
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.
11
Compact Unit / Utility Heater

IGNITION CONTROL LED

The ignition control board contains a green LED which indicates
the following:
TABLE 3
IGNITION CONTROL LED
LED
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/Check 3AMP Fuse on circuit board
Steady On
*When thermostat is placed in continuous fan mode LED will slowly flash.
LIMIT CONTROL
The limit control switch is factory set and not field adjustable.
LOUVER VANE ADJUSTMENTS
Rotate louver vanes to direct airflow upward, downward, straight,
or any combination of these directions. When unit is installed in an
inverted position, louvers may be positioned in the same manner.
COMBUSTION AIR PRESSURE SWITCH
This pressure switch checks for proper combustion air blower
operation before allowing an ignition trial. The switch is factory
set and no field adjustment is necessary. If a 3 flash LED occurs
Please make sure your venting is not blocked up. Next, remove
the end of the pressure switch tubing from the EXHAUST FAN
hose barb. There might be an obstruction in the hose barb
opening clear out the opening with a thin object that will fit inside
the hose barb. Push that through the length of the hose barb
PLUS at least another 1/2 inch, into the exhaust fan housing. This
will clear out anything stopping the vacuum from engaging the
pressure switch.
FLAME ROLLOUT SWITCH
The flame rollout switch(es) are located on the burner box top,
behind the ignition control board. This normally closed switch
opens on a temperature rise. Check for adequate combustion air
before manually resetting switch.
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.
Operating Instructions and Owner's Manual
UNIT OPERATION
Ignition control failure