Form I-XE/CRGB/RPB, Mfg No. 131782 Rev 4, Page 29
FIGURE 26 -
Johnson Controls
Metasys
®
Unit is
located in the
blower cabinet
Johnson
Controls
Metasys
®
Unit
26. Direct Digital Control System -
Model Series CRGB and RPB
The heater is equipped with a specially programmed Johnson Controls
Metasys
®
direct digital control unit. The unit is mounted in the blower
cabinet; see
FIGURE 26.
If interfacing with the building's Johnson Con-
trols Building Automaton System, follow the instructions included in
the owner's envelope. The control unit has two analog outputs, six
analog inputs, six binary outputs, and four binary inputs.
(NOTE: With the addition of a field-supplied integrator, the controller
can also be used with a Honeywell or Siebe building management sys-
tem or with any Lonworks
TM
or BacNet
TM
based protocol system.)
The unit can also operate the system as a stand alone control at the
default settings.
Depending on which option was ordered, the following functions are
available for monitoring and control through the building's environmen-
tal system. Option D1 has modulating dampers and modulating gas
control; Option D2 has on/off dampers and modulating gas control;
Option D3 has modulating dampers and two-stage gas control; Option
D4 has on/off dampers and two-stage gas control. All of the systems
with optional direct digital control systems include a firestat, freezestat,
and an air proving switch. Temperature sensors are shipped separately
and must be field-installed to monitor space temperature, discharge
temperature and the temperature of the outside air entering the system.
27. Pilot and Ignition Systems
The horizontal pilot is located in the control end of the burner rack and
is accessible after the control compartment panel has been removed. All
pilots are target type with lint-free feature. Pilot gas pressure should be
the same as supply line pressure. (See Paragraph 11.) If required, adjust
the pilot flame length to approximately 1-1/4" with pilot adjustment
screw in control valve body.
All models have a standard intermittent spark ignition pilot system.
There are two types of intermittent spark pilots - one type shuts off the
pilot gas flow between the cycles and the other not only shuts off the
pilot gas flow between cycles but also has a lockout device that stops
the gas flow to the pilot if the pilot fails to light in 120 seconds. The
lockout feature requires manual reset by interruption of the thermostat
circuit. Refer to the wiring diagram supplied with the heater for pilot
system identification and proper wiring. Spark pilot without lockout is
Flame Sensing Probe
Pilot
Orifice
Centerline of
first burner
High Tension
Lead
Burner
Rack
Front
Spark Electrode
Spark Gap
7/64 (2.78mm)
Top View
of Burner
TOP VIEW
SIDE
VIEW OF
PILOT
1/4
±
1/32
(6.38mm
±.79
)
23/32
(18.25mm)
7/16
±
1/16
(11mm
±1.6
)
Option AH2, and spark pilot with lockout is Option AH3.
NOTE:
Outdoor units in Canada using propane, require lockout. Indoor units in
U.S. and Canada, using propane require lockout.
Ignition Controller
- As part of the intermittent safety pilot systems,
the ignition controller provides the high voltage spark to ignite the pilot
gas and also acts as the flame safety device. After ignition of the pilot
gas, the ignition controller electronically senses the pilot flame. A low
voltage DC electrical signal is imposed on the separate metal probe in the
pilot assembly. The metal probe is electrically insulated from ground.
The pilot flame acts as a conduction path to ground completing the DC
circuit and proving pilot flame.
Proper operation of the electronic
spark ignition system requires a minimum flame signal of .2
microamps DC as measured by a microampmeter.
With pilot flame
proven, the ignition controller energizes the main gas valve.
If no spark occurs, check the following:
a) Voltage between blue and white terminals (non-lockout type pilot)
and Terminals 2 and 5 (lockout type pilot) on the ignition controller
should be at least 20 volts and no higher than 32 volts. Refer to
Troubleshooting (Paragraph 40) if no voltage is observed.
b) Short to ground in the high tension lead and/or ceramic insulator.
c) Pilot spark gap should be approximately 7/64".
Flash Carryover
Main
Burner
Spark Pilot
FIGURE 27 - Burner Rack
FIGURE 28 - Spark Pilot; maintain spark gap of 7/64"
NOTE:
When checking for spark with the pilot burner assembly re-
moved from the burner rack, the pilot assembly must be grounded to the
heater for proper spark.
CAUTION: Due to high voltage on pilot spark wire
and pilot electrode, do not touch when energized.
See Hazard Levels, page 2.
If the above conditions are normal and no spark occurs, replace the
ignition controller.
If the main gas valve fails to open with a normal full size pilot flame
established, check for the following:
a) Voltage between black and brown leads on the main gas valve is 20 to
32 VAC and there is no main gas flow with the builtin manual valve
in FULL OPEN position - the main valve is defective.
b) No voltage between black and brown leads on the main gas valve -
check for disconnected or shorted flame sensor lead or flame sensor
probe.
When the above conditions are normal and the main gas flow is still off,
the ignition controller is probably defective. Do not attempt to service
the ignition controller; it does not contain any replaceable components.
28. Burners and Carryover System
The furnace has individually formed steel burners with accurately die-
formed ports to give controlled flame stability without lifting or flash-
back with either natural or propane gas. The burners are lightweight and
factory mounted in an assembly which permits them to be removed as
a unit for inspection or service. The type of burner carryover system
varies with both the type of gas and the model of furnace.
