Checking Flame Rollout Control; Induced Draft Blower Motor; Checking Modulating Gas Valve; S-304A Checking Inductor Coil - Goodman GMVM Service Instructions Manual

SERVICING
AUXILIARY LIMIT
CONTROL
BLOWER HOUSING
Auxiliary Limit Control Location
S-302 CHECKING FLAME ROLLOUT CON-
TROL
A temperature activated manual reset control is mounted to
the manifold assembly on modulating furnace, as shown in
the following illustration.
FLAME
ROLLOUT
SWITCHES
* * *
*
2
*
* *
Flame Rollout Switch Location
(90% Upflow Furnace Shown, Counterflow Similar)
HIGH VOLTAGE
D ALL
ISCONNECT POWER BEFORE SERVICING OR
CHANGING ANY ELECTRICAL WIRING.
F
SOURCES MAY BE PRESENT. AILURE TO DO SO MAY CAUSE
PROPERTY DAMAGE, PERSONAL INJURY OR DEATH.
1. Turn off all power sources
2. Remove the two wires from the roll out switch
3. Using an ohmmeter, check for a closed circuit across
the two roll out switch contacts (this will be the same
reading that you see by touching your two meter leads
together).
AUXILIARY LIMIT
CONTROL
WARNING
M
ULTIPLE POWER
S-303 INDUCED DRAFT BLOWER MOTOR
Induced Draft Blower (IDB)
All modulating furnace models use a three phase induced
draft blower to draw flue gases through the heat exchanger.
The inducer uses ball bearings and is permanently
lubricated. This motor is driven at varying speeds by the
VFD (variable frequency drive) section of the IFC. The IFC
takes typical single phase power supplied to the furnace
and converts it to a three phase supply to operate the draft
inducer at the desired speed. The windings of the induced
draft motor will have equal resistance +/- 5%. Normal
resistance readings at room temperature will range from
14-17 ohms. The voltage supplied by the IFC to drive the
induced draft blower will vary from 15-110 volts A/C between
any two windings. This would be read between any two of
the three power wires between the IFC and the induced
draft blower. This voltage to the IBD will vary between furnace
models and is dependant on what percentage of maximum
fire is being called for. The power wires are colored red,
white and black. A green colored ground wire is also
present.
S-304 CHECKING MODULATING GAS VALVE
Gas ValveModulating furnaces use a 24 VAC pneumati-
cally operatedgas valve by Honeywell. The valve is ener-
gized by the inte-grated furnace control on a call for heat,
wired in series through the front-cover pressure switch. The
firing rate percentage is determined by the negative pres-
sure created by the operation of the draft inducer. The gas
valve is factory set and non-adjustable in the field. Do not
remove the seal covering the regulator screws or attempt to
adjust either of the regulator screws. Even though the modu-
lating gas valve is non-adjustable in the field, gas industry
procedure dictates that the installing / servicing technician
should know that the appliance is operating as designed
before leaving newly installed or serviced equipment. The
gas valve is equipped with 1/8 NPT fittings to access both
the inlet and manifold gas pressures. To do a manifold gas
pressure check, the furnace can be operated in field test
mode. This mode will quickly bring the furnace up to high
fire. To enter field test mode; during a call for heat, press
the fault recall button twice within a five second period; when
the dual seven segment displays show Ft, press the fault
recall button again to enter field test mode.The furnace will
stay in field test for five minutes or until the call for heat is
satisfied. Gas valve orientation must be such that the switch
is facing out towards the front of the furnace.

S-304A CHECKING INDUCTOR COIL

Wired in series with ¾ and 1 HP ECM motors; the inductor
coil conditions the power supply to the motor, smoothing
out spikes and electrical noise. With voltage applied to one
side of the inductor coil, the output voltage to the motor
should be the same as incoming voltage.
69