035-14527-000 REV A (599)
Form 650.77-N3U
18
Unitary Products Group
in your particular locality. Contract your gas company for this
information, as it varies widely from city to city.
EXAMPLE:
It is found by measurement that it takes 26 sec-
onds for the hand to turn on the 1 cubic foot dial to make a
revolution with only a 120,000 Btuh furnace running. Using
this information, locate 26 seconds in the first column of Table
5 on page17.
Read across to the column headed 1 Cubic Foot where you
will see that 138 cubic feet of gas per hour are consumed by
the furnace at that rate. Multiply 138 by 850 (the BTU rating
of the gas obtained from the local gas company). The result
is 117,300 Btuh, which is close to the 120,000 Btuh rating of
the furnace.
If the actual input is not within 2% of the furnace rating, with
allowance being made for the permissible range of the regu-
lator setting (0.3 inches W.C.), replace the orifice spuds with
spuds of the proper size.
ADJUSTMENT OF MANIFOLD GAS PRESSURE
The regulated outlet pressures, both low and high, have been
calibrated at the factory. Additional pressure adjustment
should not be necessary. If adjustment is necessary, set to
the following specifications. After adjustment, check for gas
leakage.
Low Outlet Pressure Adjustment
1.
Turn off all electrical power to the system at main fuse or
circuit breaker.
2.
Attach a manometer to the outlet pressure tap of the
valve.
3.
Turn on power and energize main and redundant (P.M.)
solenoids. Do not energize HI terminal.
4.
Remove low adjustment seal screw. (Refer to Figure 15
on page17)
5.
To increase outlet pressure, turn the 3/32" socket set
screw below the low adjustment seal screw clockwise.
To decrease outlet pressure, turn the set screw counter-
clockwise. Adjust regulator until pressure shown on
manometer matches the pressure specified on the appli-
ance rating plate.
6.
Replace low adjustment seal screw and tighten securely.
Cycle the valve several times to verify regulator setting.
7.
Remove manometer and replace the outlet pressure tap
plug.
High Outlet Pressure Adjustment
1.
Turn off all electrical power to the system at main fuse or
circuit breaker.
2.
Attach a manometer to the outlet pressure tap of the
valve.
3.
Turn on power and energize main and redundant (P.M.)
solenoids as well as the HI terminal.
4.
Remove high adjustment seal screw to expose the 3/32"
socket set screw. (Refer to Figure 15 on page17)
5.
To increase outlet pressure, turn the 3/32" socket set
screw clockwise. To decrease outlet pressure, turn the
set screw counterclockwise. Adjust regulator until pres-
sure shown on manometer matches the pressure speci-
fied on the appliance rating plate.
6.
Replace high adjustment seal screw and tighten
securely. Cycle the valve two or three times to verify reg-
ulator setting.
7.
Remove manometer and replace the outlet pressure tap
plug.
8.
Once the correct gas pressures to the burners has been
established, turn the gas valve switch to OFF and turn
the electrical supply switch OFF; then, remove the pres-
sure tap at the gas valve and re-install the plug using a
compound (on the threads) resistant to the action of LP
gases.
Be sure to relight any gas appliances that were
turned off at the start of this input check.
GAS MANIFOLD PRESSURE RANGE
NATURAL GAS
PROPANE (LP)
LOW FIRE
1.6 In. W.C.
6.5 In. W.C.
HIGH FIRE
3.5 In. W.C.
10.0 In. W.C.
The manifold pressure must be checked with the
screw-off cap in place on the pressure regulator.
If manifold pressure is too high, an over-fire condi-
tion exists which could cause heat exchanger fail-
ure. If the manifold pressure is too low, sooting
and eventual clogging of the heat exchanger could
occur.
