If the controller is being used on a boiler installation, test
it as follows:
1. Note the boiler pressure by checking the boiler pres-
sure gauge. (To perform this test properly, the boiler should
have a pressure reading near the middle of the controller's
main scale range.)
2. Turn the main scale adjusting screw (Fig. 11) until the
main scale setting indicator on the controller corresponds to
the boiler pressure gauge reading.
3. The L404A or C should break the control circuit(s)
automatically when the boiler pressure gauge reading equals
or slightly exceeds the controller setting.
The L404B or D should make the circuit under the same
The L404F; L604L,M should make the R-W circuit and
break the R-B circuit under the same circumstances.
The L604A should make the R1-W circuit and break the
R2-B circuit under the same circumstances.
4. If the controller is operating properly, turn the main
scale adjusting screw (Fig. 11) until the main scale setting
indicator is at the desired set point.
If a Controller Seems to Operate Improperly
If the controller is suspected of operating improperly, it
may be further checked as follows (Fig. 12):
1. Disconnect all power to the controller, loosen the
cover screw, and remove the cover.
2. Disconnect the wires from the controller.
3. Connect an ohmmeter between the switch terminals.
4. Lower the set point of the controller (simulating a
pressure increase) through a range greater than the differen-
tial. The switch should either make or break, depending on
the model of the controller. (An L404A or C should break, an
L404B or D should make, an L404F; L604L,M should break
R-B and make R-W, and an L604A should break R2-B and
make R1-W.) If it makes, the ohmmeter reads zero; if it
breaks, the ohmmeter reads infinity.
5. Raise the set point of the controller (simulating a
pressure decrease) through a range greater than the differen-
tial. The switch should break or make, just the opposite of its
action in step 4 (except for the L404C,D and L604L manual
NOTE: An approximation of the differential can be made by
observing the change in set point required for a resistance
change from zero to infinity.
6. If the controller operates improperly, replace it.
7. When the controller is operating properly, reconnect
the wires to the terminal block, replace the cover and tighten
the cover screw, and reconnect the power.
Do not put the system into service until you have
satisfactorily completed all applicable tests de-
scribed in this Checkout section, in the Checkout
section of the applicable instructions for the flame
safeguard control, and any others required by the
burner and boiler manufacturers.
Fig. 12—Checking controller operation using
AN L604, WITH JUMPER INSTALLED BETWEEN R1 AND R2, IS SHOWN;
AN L404F OPERATES SIMILARLY (SPDT SWITCHING). AN L404A, B, C
OR D HAS ONLY TWO TERMINALS (SPST SWITCHING); AN L404A
OR C BREAKS AND L404B OR D MAKES WHEN THE SETPOINT IS
DECREASED FAR ENOUGH.
SETTING AND CHECKOUT
(INFINITY WHEN R-B BREAKS)