Form RZ-NA-I-FT, Mfg No. 173473 Rev 8, Page 13
DANGER: Safe operation of this unit requires
proper venting flow. NEVER bypass combustion
air proving switch or attempt to operate the unit
without the venter running and the proper flow
in the vent system. Hazardous conditions could
result. See Hazard Levels, page 1.
17. Gas Valve
The main operating gas valve is powered by the 24-volt control circuit
through the thermostat and safety controls. The main control valve is
of the diaphragm type providing regulated gas flow preset at the fac-
tory.
WARNING: The operating valve is the prime safety
shutoff. All gas supply lines must be free of dirt or
scale before connecting the unit to ensure positive
closure. See Hazard Levels, page 1.
Model S izes
Star
t-U
p
Co
ld
Equilibr
ium
Set Po
int
"O
FF"
Set Po
int
"O
N
"
30
Units mfgd p rior to 11/97
-1.2
-0.70
-0.55
-0.65
45
(verify on rating p late; 11/97
-1.2
-0.70
-0.55
-0.65
60
is Serial No. Date Code AWK)
-1.2
-0.75
-0.55
-0.65
30
Units mfgd beginning 11/97
-0.9
-0.60
-0.42
-0.52
45
(verify on rating p late; 11/97
-1.1
-0.67
-0.55
-0.65
60
is Serial No. Date Code AWK)
-1.1
-0.66
-0.50
-0.60
30
Units mfgd beginning 8/98
-1.4
-0.60
-0.15
-0.25
45
(verify on rating p late; 8/98
-1.1
-0.60
-0.22
-0.32
60
is Serial No. Date Code AXH)
-1.1
-0.63
-0.22
-0.32
-1.3
-0.78
-0.55
-0.65
-1.4
-1.25
-0.80
-0.90
75, 100, 125, 150, 200
250, 300
18. Ignition System
This heater is equipped with a direct spark integrated control system.
The system monitors the safety devices and controls the operation of
the fan and venter motors and the gas valve between heat cycles.
Ignition System Operating Sequence
-- On a call for heat from the
thermostat, the system energizes the venter motor and goes through a
10-second prepurge. The system verifies that both the pressure switch
and the high limit are in the closed state. The gas valve is then ener-
gized and the ignition system provides the high voltage spark to the
electrode to ignite the main burner gas. Burner flame is electronically
sensed by the control upon carryover of all burners. (A separate solid
metal probe is used as the flame sensing function. A low voltage elec-
trical signal is imposed on the metal probe which is electrically iso-
lated from ground. When the flame impinges on the flame sensing probe,
the flame acts as a conduction path to ground. The flame rectifies and
completes the DC circuit, and the ignition system acknowledges the
flame.) The fan motor is energized by the system after 30 seconds of
flame sensing.
After the thermostat has been satisfied, the system de-energizes the gas
valve, the venter motor goes through a 45-second post-purge, and the
fan motor remains energized for an additional 180 seconds.
NOTE:
This is a three trial system, should the unit not sense burner
flame, the unit will lockout for one hour before initiating another trial
for ignition. To initiate another trial for ignition before the one hour,
requires that either the thermostat be reset or the power to the unit be
interrupted for 30 seconds.
19. Burners
This unit heater has inshot burners designed to provide controlled flame
stability without lifting or flashback 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.
20. Burner Air Restrictor
Sizes 250 and 300 burning propane gas are equipped with a two-piece
burner air restrictor. The air restrictor is attached to the burner assem-
bly and is not field adjustable.
16. Combustion Air Proving
Switch
The combustion air proving switch is a pressure sensitive switch that
monitors air pressure to ensure that proper combustion air flow is avail-
able. The switch is a single pole - normally open - device which closes
when a decreasing pressure is sensed in the venter housing.
On start-up when the heater is cold, the sensing pressure is at the most
negative level, and as the heater and flue system warm up, the sensing
pressure becomes less negative. After the system has reached equilib-
rium (about 20 minutes), the sensing pressure levels off.
If a restriction or excessive flue length or turns cause the sensing pres-
sure to be outside the switch setpoint, the pressure switch will function
to shut off the main burners. The main burners will remain off until the
system has cooled and/or the flue system resistance is reduced. The
Table below lists the approximate water column negative pressure read-
ings and switch setpoints for sea level operating conditions.