UTC SCS-5-08-3 Installation Instructions And Homeowner's Manual page 36

3.1.4) Sequence of operation of the SCS
Note: Refer to electric wiring diagram (figure 13)
When the thermostat call for heat, a 120 volts tension
is applied on # 1 and # 2 terminals strip of the SCS
electrical box. Then, the CR-1 normally close contact
(NC) of the relay is closed, the TDR-1 delay relay
contact is open and no current is going to R-1 coil or L-
1 light. The electric power is applied on terminal strip
#3 and #4 and the burner start to run. A pre-purge
function integrated in the burner control will run before
ignition for a period between 10 and 30 seconds.
3.1.5) Effects on pressure switch
When the burner starts, a pressure is created in the ''
pressure '' silicone tubing and a vacuum is created in
the '' vacuum'' silicone tubing. It is important to know
that the pressure act in the same way on the
diaphragm pressure switch. In less then 4 seconds,
the total pressure (addition of the pressure and
vacuum) should stabilize between 0.20'' and 0.70''
W.C. The PS-1 normally open contact close at a
pressure of 0.8'' W.C. and more. Therefore, the
contacts PS-1 is open in normal operation of the
heating unit. For total pressure testing, pressure and
vacuum testing, refer to figure 14.
16
3.1.6) Abnormal
indicator light L-1 is ON)
If the PS-1 contact closes and the TDR-1 contact is
closed (after 4 seconds) the electric power is applied
on the R-1 coil. The CR-1 normally closed contact
opens and the burner shuts down. In this case, the
lock out indicator light stays open. To restart the
system, the electrical supply must be turned off
and back on.
3.1.7) Troubleshooting guide
If the burner stop after 4 seconds and the L-1 light
of the SCS control box is on, perform the
following verifications :
•
Verify if the SCS electrical box is in vertical
position (Refer to instructions section 2 for correct
positioning);
•
Verify that the pressure switch are in working order
by measuring the total pressure (the vacuum and
the pressure). Refer to figure 14 for testing (install
jumper between # 1 and # 4). The burner cover
must also be in place;
- The total pressure must not be more then 0.8''
W.C. If it is the case, the pressure and vacuum
can be verified separately to identify the
problem;
- If the pressure value is greater then 0.8''W.C.,
there is an obstruction in the flue pipe;
- If the vacuum value is greater then 0.8 '' W.C.,
there is an obstruction in the air inlet.
operation (Lock out