60-2159—8
7
C645A-E PRESSURE SWITCHES
The C645B spring-loaded diaphragm actuates the Micro
Switch snap-acting switch which breaks a control circuit, locks
out, and turns on an alarm (if so wired) when the pressure
rises to the scale setting. When pressure falls to the scale
setting minus the differential, the switch lockout can be
manually reset, turning off the alarm
Checkout
C645A,B—Gas or Air Switch
Set cutoff pressure.
Open main supply line. Depress reset lever on lockout
models until switch makes R-W.
Set controller and limit switch to call for heat.
For C645A—close main shutoff valve. Valve should
close when pressure reaches cutoff point.
For C645B—wait a few minutes for the pressure to rise;
then lower the scale setting until the switch makes R-W
and locks out.
NOTE:
To more accurately check C645A, use slow
bleedoff. For C645B, jumper other limit and let
pressure rise to cutoff setting.
For C645A—reconnect the control valve, open the
shutoff valve, press the reset lever (if necessary), and
return the pressure switch to its original setting.
For C645B—raise setting to normal. Depress reset
lever.
Allow system to operate through at least one complete
cycle to make certain all components are functioning
properly.
C645C,D—Air Switch Only
Set cutoff pressure.
Turn on fan.
If using a manual rest C645, depress and hold lever
until switch makes R-W.
Block fan inlet or filter area. Switch should break R-W,
make R-B when pressure drops to cutoff point. Manual
reset models lock out.
Remove obstruction. Depress reset lever and allow
system to operate through at least one complete cycle
to make certain all components are functioning
properly.
C645E1002—Distillate Fuel Oil Switch
The C645E1002 is the same as the C645A1006 Gas
Pressure Switch except the C645E1002 has a 0.125 in.
NPT main connection in its pressure chamber.
See Checkout for C645A.
LOCKING
SCREW
23466 ADJUSTING
WRENCH
SCALEPLATE
STOP
SET POINT INDICATOR
M7562
Fig. 6. Adjusting C645B1047 scaleplate stop.
Manual Resetting
The C645A,C manual reset models lock out at scale setting
minus the differential and require manual resetting after the
pressure rises to scale setting to resume normal operation.
The C645B locks out at scale setting and requires manual
resetting after the pressure falls to scale setting minus the
differential to resume normal operation. To reset, push the
reset button as far as it will go; then release.
IMPORTANT
Lockout models cannot be made to recycle
automatically by permanently holding in the reset
lever.
OPERATION AND CHECKOUT
Operation
The C645A,C,D,E spring-loaded diaphragm actuates the
Micro Switch snap-acting switch to break a control circuit
when pressure falls to scale setting minus differential. The
switch can be wired to turn on an alarm at the same time.
When the pressure rises to the scale setting, the control
circuit requires manual resetting to reset and turn off alarm.
Optional C645A model will recycle automatically when the
control circuit returns to scale setting.
