Service manual

SERVICING
23
To adjust the pressure regulator on the gas valve, turn down
(clockwise) to increase pressure and input, and out (coun-
terclockwise) 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 gas and with
proper inlet pressures and correct piping size, full capacity
will be obtained.
With propane gas, no unit gas valve regulator is used; how-
ever, the second stage supply line pressure regulator should
be adjusted to give 11" water column with all other gas con-
suming appliances running.
The dissipation of the heat transferred to the heat exchanger
is now controlled by the amount of air circulated over its
surface.
The amount (CFM) of air circulated is governed by the ex-
ternal static pressure in inches of water column of duct work,
cooling coil, registers and etc., applied externally to the unit
versus the motor speed tap.
A properly operating unit must have the BTU 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 increase. Consult the proper
tables for temperature rise limitation.
To find the BTU input, multiply the number of cubic feet of
gas consumed per hour by the heating value of the gas
being used. (The calorific value of the gas being used is
found by contacting your local utility.)
Example:
It is found by the gas meter, that it takes forty (40) seconds
for the hand on the cubic foot dial to make one complete
revolution, with all appliances off, except the furnace. Take
this information and locate it on the gas rate chart. Ob-
serve the forty (40) seconds, locate and read across to the
one (1) cubic foot dial column. There we find the number
90, which shows that ninety (90) cubic feet of gas will be
consumed in one (1) hour.
Let's assume the local gas utility has stated that the calo-
rific value of the gas is 1025 BTU.
Multiplying the ninety (90) cubic feet by 1025 BTU gives us
an input of 92,250 BTUH.
Checking the BTU input on the rating plate of the furnace
being tested.
EXAMPLE: PGB30C0902D
INPUT: 90,000 BTU/HR
OUTPUT CAP: 72,000
Should the figure you calculated not fall within five (5) per-
cent of the nameplate rating of the unit, adjust the gas valve
pressure regulator or resize orifices. In no case should
the input exceed that shown on the rating plate.
CAUTION
ALWAYS CONNECT A MANOMETER TO THE 1/8" PIPE
TAP AT THE GAS VALVE BEFORE ADJUSTING THE
PRESSURE REGULATOR. IN NO CASE 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.