Goodman GMEC80 Service Instructions Manual page 33

SERVICING
In some areas the gas supplier may artificially derate the
gas in an effort to compensate for the effects of altitude. If
the gas is artificially derated the appropriate orfice size must
be determined based on the BTU/ft
gas and the altitude. Refer to the National Fuel Gas Code,
NFPA 54/ANSI Z223.1, and information provided by the gas
supplier to determine the proper orifice size.
CHECKING FOR DELAYED IGNITION
Delayed ignition is a delay in lighting a combustible mixture
of gas and air which has accumulated in the combustion
chamber.
Furnace design makes this extremely unlikely unless safety
controls have been by-passed or tampered with. Never by-
pass or alter furnace controls.
If delayed ignition should occur, the following should be
checked:
1. Improper gas pressure - adjust to proper pressure.
2. Improper burner positioning - burners should be in
locating slots, level front to rear and left to right.
3. Carry over (lighter tube or cross lighter) obstructed -
clean.
4. Main burner orifice(s) deformed, or out of alignment to
burner - replace.
CHECKING INTEGRATED IGNITION
CONTROL BOARDS
NOTE: Failure to earth ground the furnace, reversing the
neutral and hot wire connection to the line (polarity), or a
high resistance connection in the neutral line may cause
the control to lockout due to failure to sense flame.
T
O AVOID THE RISK OF ELECTRICAL SHOCK, WIRING TO THE UNIT
MUST BE PROPERLY POLARIZED AND GROUNDED.
BEFORE PERFORMING SERVICE LISTED BELOW.
The ground wire must run from the furnace all the way back
to the electrical panel. Proper grounding can be confirmed
by disconnecting the electrical power and measuring re-
sistance between the neutral (white) connection and the
burner closest to the flame sensor. Resistance should be
less than 2 ohms.
The ignition control is a combination electronic and elec-
tromechanical device and is not field repairable. Complete
unit must be replaced.
L
INE VOLTAGE NOW PRESENT
These tests must be completed within a given time frame
due to the operation of the ignition control.
The ignition control is capable of diagnosing many furnace
failures to help in troubleshooting. The trial for ignition
content of the derated
3
WARNING
D
ISCONNECT POWER
WARNING
period is 4 seconds.
Goodman
® Brand and Amana® Brand Two-Stage
1. Check for 120 volts from Line 1 (Hot) to Line 2 (Neutral)
at the ignition control. No voltage, check the door switch
connections and wire harness for continuity.
2. Check for 24 volts from W to C terminal on the ignition
control. No voltage. Check transformer, room thermo-
stat, and wiring.
If you have 24 volts coming off the transformer but
receive approximately 13 volts on the terminal board
between (C) and (R), check for blown fuse.
3. Check 120 volt outputs on the 5 pin harness.
Pin 1 = HSI Hot
Pin 2 = Inducer High
Pin 3 = Inducer Low
Pin 4 = Inducer N
Pin 5 = HSI N
4. After the ignitor warmup time, begin checking for 24
volts to the gas valve. Voltage will be present for four
seconds only if proof of flame has been established.
5. If proof of flame was established voltage will be provided
to the air circulation blower following the heat on delay
period.
CHECKING FLAME SENSOR
A flame sensing device is used in conjunction with the igni-
tion control module to prove combustion. If proof of flame is
not present the control will de-energize the gas valve and
"retry" for ignition or lockout.
HIGH VOLTAGE
D ALL
ISCONNECT POWER BEFORE SERVICING OR
M
INSTALLING THIS UNIT. ULTIPLE POWER SOURCES MAY
F
BE PRESENT. AILURE TO DO SO MAY CAUSE PROPERTY
DAMAGE, PERSONAL INJURY OR DEATH.
Flame current can be measured in two ways:
1. Putting a D.C. microamp meter in series with the
flame rod
2. Putting a D.C. volt meter across the two solder pads
in the flame current section of the control board.
1 D.C. volt = 1 microamp.
WARNING
33