Goodman Amana AMH8 Service Instructions Manual page 46

MAINTENANCE
Let's assume the local gas utility has stated that the
calorific value of the gas is 1,025 BTU per cubic foot.
Multiplying the ninety (90) cubic feet by 1,025 BTU per
cubic foot gives us an input of 92,250 BTUH.
Checking the BTU input on the rating plate of the fur-
nace being tested.
EXAMPLE:
INPUT: 92,000 BTU/HR
OUTPUT CAP: 84,000
Should the figure you calculated not fall within five (5)
percent of the nameplate rating of the unit, adjust the
gas valve pressure regulator or resize orifices.
A
LWAYS CONNECT A MONOMETER TO THE OUTLET TAP AT THE GAS
VALVE BEFORE ADJUSTING THE PRESSURE REGULATOR.
SHOULD THE FINAL MANIFOLD PRESSURE VARY MORE THAN PLUS OR
MINUS .3 INCHES WATER COLUMN FROM 3.5 INCHES WATER COLUMN
FOR NATURAL GAS OR 10 INCHES WATER COLUMN FOR PROPANE GAS.
To adjust the pressure regulator on the gas valve, turn
down (clockwise) to increase pressure and input, and
out (counterclockwise) to decrease pressure and input.
Since normally propane gas is not installed with a gas
meter, clocking will be virtually impossible. The gas
orifices used with propane are calculated for 2500 BTU
per cubic foot gas and with proper inlet pressures and
correct piping size, full capacity will be obtained.
46
CAUTION
I
N NO CASE
With propane gas, no unit gas valve regulator is used;
however, the second stage supply line pressure regula-
tor should be adjusted to give 11" water column with all
other gas consuming appliances running.
The dissipation of the heat transferred to the heat ex-
changer is now controlled by the amount of air circu-
lated over its surface.
The amount (CFM) of air circulated is governed by the
external static pressure in inches of water column of
duct work, cooling coil, registers, etc., applied exter-
nally to the unit versus the motor speed tap (direct
drive).
A properly operating unit must have the BTU per hour
input and CFM of air, within the limits shown to prevent
short cycling of the equipment. As the external static
pressure goes up, the temperature rise will also in-
crease. Consult the proper tables for temperature rise
limitation.