Goodman GMVM Service Instructions Manual page 50

OPERATION
1. Turn OFF gas to furnace at the manual gas shutoff
valve external to the furnace.
2. Connect a calibrated water manometer (or appropriate
gas pressure gauge) at either the gas valve inlet pres-
sure boss or the gas piping drip leg. See Honeywell
VR9205R gas valve figure for location of inlet pressure
boss.
NOTE: If measuring gas pressure at the drip leg or Honeywell
VR9205R gas valve, a field-supplied hose barb fitting must be
installed prior to making the hose connection.
3. Turn ON the gas supply and operate the furnace and
all other gas consuming appliances on the same gas
supply line.
Field Test Mode is intended to help a service person
troubleshoot and check out an installed appliance.
To enter Field Test Mode the Fault Recall Push-But-
ton
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 dis-
play will show the normal "Hi" while the control is firing
at 100%. If the Fault Recall Push-Button has not
been pressed within 5 seconds of displaying "Ft" the
display will revert back to normal.
4. Measure furnace gas supply pressure with burners firing.
Supply pressure must be within the range specified in the
Inlet Gas Supply Pressure table.
Inlet Gas Supply Pressure
Natural Gas Minimum:
Propane Gas Minimum: 11.0" w.c.
If supply pressure differs from table, make the necessary adjust-
ments to pressure regulator, gas piping size, etc., and/or con-
sult with local gas utility.
5. Turn OFF gas to furnace at the manual shutoff valve and
disconnect manometer. Reinstall plug before turning on
gas to furnace.
6. Turn OFF any unnecessary gas appliances stated in step
3.
50
4.5" w.c. Maximum: 10.0" w.c.
Maximum: 13.0" w.c.
Gas Line
Gas
Shutoff
Valve
Drip Leg Cap
With Fitting
Manometer Hose
Measuring Inlet Gas Pressure (Alt. Method)
G M P M
AS ANIFOLD RESSURE
T
O PREVENT UNRELIABLE OPERATION OR EQUIPMENT DAMAGE
GAS MANIFOLD PRESSURE MUST BE AS SPECIFIED ON THE UNIT RATING
. G
PLATE AS VALVE IS FACTORY SET AND DOES
F . D
IELD ADJUSTMENT O NOT ATTEMPT TO ADJUST VALVE
The manifold pressure must be measured with the burners oper-
ating. To measure the manifold pressure, use the following
procedure.
1. Turn OFF gas to furnace at the manual gas shutoff valve
external to the furnace.
2. Turn off all electrical power to the system.
3. Outlet pressure tap connections: Remove the outlet pres-
sure boss plug. Install an 1/8" NPT hose barb fitting into the
outlet pressure tap.
4. Attach a hose and manometer to the outlet pressure
barb fitting.
5. Turn ON the gas supply.
6. Turn on power and close thermostat "R" and "W1" con-
tacts to provide a call for low stage heat.
7. Modulating furnaces light at 80% of max input. For natu-
ral gas the expected manifold pressure at ignition will be
in a range of 1.8" - 2.5" WC. For LP gas the range will be
5.8" - 6.8" WC.
NOTE: Measure the gas manifold pressure with the burn-
ers firing. After every time the main power is turned off
and back on, the furnace will enter a calibration routine
on the next call for heat The inducer will ramp up and
down during the calibration routine. After calibration, the
furnace will proceed to ignition cycle.
Gas Line
To Furnace
Open To
Atmosphere
Manometer
EASUREMENT
CAUTION
,
NOT
REQUIRE ANY
.
THE