Patterson-Kelley MOD-04 Manual De Usuario

 27 

 

 
1.  When the On/Off (Main power) switch is turned 

on, the switch illuminates.  Power is provided to 
the flame safeguard control, the temperature 
control, and through normally closed contacts of 
relays 2 and 3 to the damper close terminal.  
Power is also applied through the “start logic 
string”  a series of normally closed switches, in-
cluding water flow, gas pressure, high stack 
temp, high limit temperature, and operating 
temperature to the flame safeguard programmer. 

2.  The water flow limit switch is closed when 

there is water flow through the boiler. 

Note: The closing of this switch does not prove 
that flow is adequate.  Refer to Technical Data 
Sheet # TD110 for proper flow requirements.   

3.  When adequate gas pressure is available, the 

low gas pressure limit switch is closed.  Manual 
reset is required following conditions resulting 
in low gas pressure. 

4.  When the temperature sensed by the high limit 

temperature control is below the set limit, the 
switch is closed.  Manual reset is required fol-
lowing conditions exceeding high limit tempera-
ture. 

5.  When heat is required as indicated by the outlet 

water temperature, power is applied to Terminal 
6 of the programmer, which initiates the burner 
ignition and operation sequence. 

6.  The programmer first energizes Terminal 4 

which supplies power to a normally open con-
tact of relay 2, the air damper position limit 
switch, and the air flow switch.  If the damper 
motor is on the low fire side of the damper posi-
tion limit switch, relay 3 is energized through 
normally closed contact of relay 2. This supplies 
power to the open terminal of the air damper 
through the normally open contact of relay 3. 
The air damper opens to its start position and 
the damper position limit switch applies power 
to terminal 6 on the damper motor.  This ener-

gizes relay 2 and stops the air damper motor. 
The motor contactor is energized through relay 
2.    The air flow switch initially shows low air 
flow with the “LOW AIR” indicator.  This indi-
cator will remain on until sufficient air flow is 
sensed.  If the damper motor is not open enough 
for purge, relay 2 is not energized, the combus-
tion air blower will not start and the combustion 
sequence does not go any farther. 

7.  Once sufficient airflow is indicated by the air 

flow switch, Terminal 7 of the combustion con-
trol is energized.  This starts the Prepurge pe-
riod.  The combustion chamber is Prepurged for 
30 seconds. 

8.  A 10-second “trial for ignition” period is initi-

ated with both Terminal 8 and 10 being ener-
gized. Terminal 10 of the combustion control 
powers the ignition transformer.  The trans-
former output creates a spark at the igniter.  
Terminal 8 powers the pilot gas valve. 

9.  When a pilot flame is detected by the UV scan-

ner a signal is sent to the combustion control.  
When this signal is detected, Terminal 10 of the 
combustion control is de-energized terminating 
the spark. 

10.  After the 10 second “trial for ignition” period, if 

pilot flame has been established, Terminal 9 of 
the Combustion Control is energized.  This 
opens the main gas valve and energizes the air 
gas ratio control.  The 10 second Main trial for 
ignition” period begins.  If pilot flame has not 
been established, the unit will lock out on pilot 
flame failure. 

11.  After the 10 second “main trial for ignition pe-

riod” if flame has been established, Terminal 8 
of the combustion control is de-energized, clos-
ing the pilot valve.  Terminal 21 is energized, 
energizing Relay-1.  If main flame has not been 
established, the unit will lock out on main flame 
failure. 

12.  Relay 1 releases the temperature control to 

modulate. 

13.  The unit modulates between the low fire setting 

and the high fire setting to maintain the desired 
outlet water temp set point.