Goodman GMVM Service Instructions Manual page 51

OPERATION
8. Field Test Mode is intended to help a service person
troubleshoot and check out an installed appliance by
bringing the furnace up to High fire (100% input), by-pass-
ing the normal modulating routine.
To enter Field Test Mode the Fault Recall Push-Button
must be pressed twice within a 5 second period at any
time during a heating cycle, at which time the display will
show "Ft". While the display is showing "Ft", pressing
and holding the Fault Recall Push-Button for 3 seconds
will enable the field test mode and override the normal
firing rate sequence at a rate of 100% for 5 minutes or
until the end of the call for heat. The display will show the
normal "Hi" while the control is firing at 100%. If the Fault
Recall Push-Button has not been pressed within 5 sec-
onds of displaying "Ft" the display will revert back to nor-
mal.
NOTE: Gas valve is factory set and does NOT require
any field adjustment. Do NOT attempt to adjust valve.
9. Turn off all electrical power and gas supply to the sys-
tem.
10. Remove the manometer hose from the hose barb fitting.
11. Remove the 1/8" NPT hose barb fitting from the outlet
pressure tap. Replace the outlet pressure boss plug and
seal with a high quality thread sealer.
12. Turn on electrical power and gas supply to the system.
13. Close thermostat contacts "R" and "W1/W2" to energize
the valve.
Using a leak detection solution or soap suds, check for leaks at
outlet pressure boss plug. Bubbles forming indicate a leak. SHUT
OFF GAS AND REPAIR ALL LEAKS IMMEDIATELY!
NOTE: For natural gas to LP conversion, consult the furnace
Specification Sheet.
Manifold Gas Pressure
Gas
Natural High Stage
Propane High Stage
G I R M
AS NPUT ATE EASUREMENT
The gas input rate to the furnace must never be greater than that
specified on the unit rating plate. To measure natural gas input
using the gas meter, use the following procedure.
1. Turn OFF the gas supply to all other gas-burning appli-
ances except the furnace.
2. While the furnace is operating, time and record one
complete revolution of the smallest gas meter dial.
3. Calculate the number of seconds per cubic foot (sec/
3
ft ) of gas being delivered to the furnace. If the dial is a
one cubic foot dial, divide the number of seconds re-
corded in step 2 by one. If the dial is a two cubic foot
dial, divide the number of seconds recorded in step 2
by two.
Range Nominal
3.2 - 3.8" w.c. 3.5" w.c.
9.5 - 10.5" w.c. 10.0" w.c.
(N G O )
ATURAL AS NLY
4. Calculate the furnace input in BTUs per hour (BTU/hr).
Input equals the sum of the installation's gas heating
value and a conversion factor (hours to seconds) di-
vided by the number of seconds per cubic foot. The
measured input must not be greater than the input indi-
cated on the unit rating plate.
EXAMPLE:
Installation's gas heating (HTG) value: 1,000 BTU/ft
(Obtained from gas supplier)
Installation's seconds per cubic foot: 34 sec/ ft
Conversion Factor (hours to seconds): 3600 sec/hr
Input = (Htg. value x 3600) ÷ seconds per cubic foot
Input = (1,000 BTU/ft
Input = 106,000 BTU/hr
NOTE: The final manifold pressure cannot vary by more than ±
0.3" w.c. for Natural and + 0.5" for LP from the specified setting.
Consult your local gas supplier if additional input rate adjustment
is required.
5. Turn ON gas to and relight all other appliances turned
off in step 1. Be certain that all appliances are func-
tioning properly and that all pilot burners are operating.
Temperature Rise
Temperature rise must be within the range specified on the unit
rating plate. An incorrect temperature rise may result in condens-
ing in or overheating of the heat exchanger. An airflow and tem-
perature rise table is provided in the Specification Sheet appli-
cable to your model. Determine and adjust temperature rise as
follows:
1. Operate furnace with burners firing for approximately
ten minutes. Ensure all registers are open and all duct
dampers are in their final (fully or partially open) posi-
tion.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must
not be influenced by radiant heat by being able to "see"
the heat exchanger.
3. Subtract the return air temperature from the supply air
temperature to determine the air temperature rise. Al-
low adequate time for thermometer readings to stabi-
lize.
4. Adjust temperature rise by adjusting the circulator
blower speed. Increase blower speed to reduce tem-
perature rise. Decrease blower speed to increase tem-
perature rise. Refer to Startup Procedure and
Adjustment -Circulator Blower Speeds for speed
changing details.
3 x 3600 sec/hr) ÷ 34 sec/ ft
3
3
3
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