035-17438-001 Rev. A (901)
Unitary Products Group
15
6.
Replace high adjustment seal screw and tighten
securely. Cycle the valve two or three times to verify reg-
ulator setting.
7.
Once the correct high outlet gas pressure to the burners
has been set adjust the low outlet pressure per the
adjustment procedure detailed in the next section..
Low Outlet Pressure Adjustment
1.
Adjust the thermostat so the furnace will operate at low
fire.
2.
Refer to Figure 11, for the location of the pressure regu-
lator adjustment cap and screw on main gas valve.
3.
Remove low adjustment seal screw, see Figure 11.
4.
To
increase
outlet pressure, turn the 3/32” 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.
5.
Replace low adjustment seal screw and tighten securely.
Cycle the valve several times to verify regulator setting.
6.
Turn off gas and electricity and remove manometer and
gas valve tap and replace the outlet pressure tap plug.
7.
Turn the electrical and gas supplies back on, and with
the burners in operation, check for gas leakage around
the plug with a soap and water solution.
ADJUSTMENT OF TEMPERATURE RISE
Direct Drive Motors
(only applies to PSC replacement)
The temperature rise, or temperature difference between the
return air and the heated air from the furnace, must be within
the range shown on the furnace rating plate. Application limi-
tations are shown in Table 1 or 2. After the temperature rise
has been determined, the cfm can be calculated.
After about 20 minutes of operation, determine the furnace
temperature rise. Take readings of both the return air and the
heated air in the ducts, about six feet from the furnace where
they will not be affected by radiant heat.
Table 4:
GAS RATE (CUBIC FEET PER HOUR)
SECONDS FOR
ONE REVOLUTION
SIZE OF TEST DIAL
1/2 CUBIC FT
1 CUBIC FT
10
180
360
12
150
300
14
129
257
16
113
225
18
100
200
20
690
180
22
82
164
24
75
150
26
69
138
28
64
129
30
60
120
32
56
113
34
53
106
36
50
100
38
47
95
40
45
90
42
43
86
44
41
82
46
39
78
48
37
75
50
36
72
52
35
69
54
34
67
56
32
64
58
31
62
60
30
60
The manifold pressure must be checked with the
screw-off cap in place on the pressure regulator.
If manifold pressure is too high, an overfire condition
exists which could cause heat exchanger failure. If
the manifold pressure is too low, sooting and even-
tual clogging of the heat exchanger could occur.
Be sure that the gas valve pressure regulator cap is
replaced.
FIGURE 11 :
Gas Valve - (Top) Manual On/OFF Switch
(Bottom) Regulator Adjustments
R
E
P
LA
CE
R
E
P
LA
CE
SCRE
W
SCRE
W
INLET
OUTLET
ON / OFF SWITCH
WRENCH
BOSS
LOW FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
HIGH FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
HI ADJUST
LO
ADJUST
PM
C
HI
O
F
F
ON
