44
I-EEDU (02-21) 150492-A
OPERATION—CONTINUED
Startup—Continued
Table 20. Operating Sequence
Operation
Result
1 . Set thermostat to lowest setting
—
2 . Turn ON power to unit
3 . Turn ON main and pilot manual gas valves
4 . Set thermostat to desired setting
Thermostat calls for heat, which energizes venter motor
Pressure switch closes, which energizes pilot gas valve and spark gap to produce pilot flame
on each operating cycle
Sensing probe proves presence of pilot flame and energizes safety switch portion of control
Switch action deenergizes spark gap and energizes main gas valve
On units with optional fan control, fan control senses heat exchanger temperature, which
energizes fan or blower motor of air handler
If pilot flame is extinguished during main burner operation, sensing probe detects absence of
flame and causes safety switch to close main valve
On units with standard intermittent spark pilot systems, spark gap recycles
On units with optional spark ignition with lockout, if pilot is not established within timing cycle
(approximately 120 seconds), unit locks out and must be reset by interrupting power to
control circuit
Post-Startup Checklist
With unit in operation, measure manifold gas pressure—pressure for natural gas should be 3 .5 IN WC and 10 IN
WC for propane gas (refer to
Manifold Gas Pressure Measurement and Adjustment
section) .
Turn unit OFF and ON, pausing two minutes between each cycle—observe for smooth ignition .
On two-stage or modulating burner systems, manipulate temperature adjustment slowly up and down to see if
control is sequencing or modulating properly—raising temperature setting drives burner ON or to full fire .
Observe burner flame at full fire—natural gas flame should be about 1-1/2 inches in height with blue coloring .
Propane gas flame at full fire should be about 1-1/2 inches in height with blue coloring . Yellow tipping may appear
on propane gas . If yellow extends beyond 1/2 to 3/4 inch, adjust air shutters (refer to
section) .
Check limit control—with heater on, completely block off distribution air—limit control should open within few
minutes, shutting off gas supply to main burners .
Place owner’s envelope that contains Limited Warranty Card, this manual, and any optional information in
accessible location near heater—follow instructions on envelope .
ADJUSTMENTS
The adjustments described in the following paragraphs can be accomplished only after the heater is in operation .
Manifold Gas Pressure Measurement and Adjustment
NOTE: Consult the valve manufacturer’s literature provided with the furnace for more detailed
information.
⚠ WARNING ⚠
Manifold gas pressure must never exceed 3.5 IN WC for natural gas or 10 IN WC for propane gas.
Normally, adjustment to the factory-preset regulator should not be necessary . Before attempting to measure or adjust
manifold gas pressure, the inlet (supply) pressure must be within the specified range for the gas being used, both
when the heater is in operation and when on standby . Incorrect inlet pressure could cause excessive manifold gas
pressure immediately or at some future time . Measure and adjust the manifold gas pressure as follows:
NOTE: A manometer (fluid-filled gauge) with an inches water column scale is recommended for
gas pressure measurement rather than a spring-type gauge due to the difficulty of maintaining
the calibration of a spring-type gauge.
