Enerco HSU 75 User Manual

enerco | Compact Unit Heater

operating Instructions and owner’s Manual

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.

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. 

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, 
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. 

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

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. 

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. 

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

 

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.