Reznor MAPS II Unit Installation Manual - Manual (Page 41)

Form I-MAPS II, P/N 206131 (Rev 13), Page 41
Gas Capacity Controls
The gas train is equipped with either 3:1 turndown gas capacity control ( FIG-
URE 33A or 35A) or optional 6:1 turndown (FIGURE 33B or 35B). Both the 3:1
and 6:1 system have a split burner design (1/3 and 2/3) with two single-stage
gas valves in heat section Sizes 100, 150, 200, 250, and 300. Heat section
Sizes 350, 400, 350, 500, 550, 600, 650, and 700 have two section burners.
One section is split 1/3 and 2/3 and the other is a "non-split" burner. Two single-
stage gas valves feed the split burner and a third single-stage gas valve feeds
the non-split burner.
The optional 6:1 turndown system includes a modulating/regulating valve and
a power signal converter ( FIGURE 34). Control is through the system cooling/
heating controller (See Paragraph 8) based on heating air setpoint and inlet air
temperature. NOTE: Propane gas systems are 3:1 turndown (6:1 is available
with natural gas only).
FIGURE 33A - Gas
Train for Heat
Section Sizes 100-
400 showing Furnace
with 3:1 Turndown
(Option AG55)
and both optional
Low and High Gas
Pressure Switches
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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 2.
Supply Pressures - Before attempting to measure valve outlet gas pressure,
the inlet supply pressure must be within the specified range both when the
heater is in operation and on standby. Incorrect inlet pressure could cause
excessive valve outlet gas pressure immediately or at some future time.
Natural gas inlet supply pressure for the 3-stage gas control system must be a
minimum of 5.5" w.c. Minimum natural gas supply pressure for the modulating
6:1 gas control system is 6.0" w.c.
Maximum natural gas supply pressure is 14" w.c.
If natural gas supply pressure is too high, install a regulator in the supply line
before it reaches the heater. If natural gas supply pressure is too low, contact
your gas supplier.
Propane gas inlet supply pressure must be a minimum of 11" w.c. and a maxi-
mum of 14" w.c.
CAUTION: DO NOT bottom out the gas valve regulator adjust-
ing screw. This can result in unregulated manifold pressure
causing excess over-fire and heat exchanger failure