Manifold Gas Pressure Adjustment; Single Stage; Two Stage - York International ZQ Series Installation Manual

Table 59: Gas Rate Cubic Feet Per Hour
Seconds forOne Rev.
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
60
Note: To find the Btu input, multiply the
number of cubic feet of gas consumed
per hour by the Btu content of the gas in
your particular locality (contact your gas
company for this information as it varies
widely from area to area).
EXAMPLE
By actual measurement, it takes 19 seconds for the
hand on a 1 cubic foot dial to make a revolution
with a 200,000 Btuh furnace running. To determine
rotations per minute, divide 60 by 19 = 3.16. To
calculate rotations per hour, multiply 3.16 • 60 =
189.6. Multiply 189.6 • 1 (0.5 if using a 1/2 cubic foot
dial) = 189.6. Multiply 189.6 • (the Btu rating of the
gas). For this example, assume the gas has a Btu
rating of 1050 Btu/ft . The result of 199,000 Btuh is
3
within 2% of the 200,000 Btuh rating of the furnace.
Manifold Gas Pressure
Adjustment

Single Stage

About this task:
This gas furnace has one stage of gas heat.
Therefore, the gas valve has one adjustment screw
located under a cover screw on the valve (See Figure
30).
Manifold pressure adjustment procedure.
1. Turn off all power to the unit.
2. Using the outlet pressure port on the gas
valve, connect a manometer to monitor the
manifold pressure.
Size of Test Dial
1/2 cu. ft. 1 cu. ft.
60 120
56 113
53 106
50 100
47 95
45 90
43 86
41 82
39 78
37 75
36 72
35 69
34 67
32 64
31 62
30 60
Johnson Controls Ducted Systems
3. Remove cover screw covering the pressure
adjustment screw.
4. Turn on power to the unit.
5. Set thermostat to call for heat and start
furnace.
6. If necessary, using a screwdriver, turn the
adjustment screw clockwise to increase
manifold pressure or counterclockwise to
decrease manifold pressure.
7. Once pressure has been checked, replace the
plastic cap covering the pressure adjustment
screw.

Two Stage

About this task:
This gas furnace has two heat stages. Therefore, the
gas valve has two adjustment screws located under
two cover screws. The second stage adjustment
screw is adjacent to the "HI" marking on the valve
and the first stage adjustment screw is located
adjacent to the "LO" marking on the valve (See
Figure 31).
Manifold pressure adjustment procedure.
Adjust second stage (Refer to Table 60 for input
value.) pressure first, then adjust first stage (Refer
to Table Table 60 for input value.) pressure.
1. Turn off all power to the unit.
2. Using the outlet pressure port on the gas
valve, connect a manometer to monitor the
manifold pressure.
3. Remove cover screws covering HI and LO
pressure adjustment screws.
4. Turn on power to the unit.
5. Set thermostat to call for second stage heat
and start furnace.
6. If necessary, using a screwdriver, turn
thesecond stage adjustment screw
(adjacent to the "HI" marking on the valve)
clockwise to increase manifold pressure
or counterclockwise to decrease manifold
pressure.
7. After the high manifold pressure has been
checked, adjust the thermostat to call for first
stage heat.
INSTALLATION MANUAL ZQ SERIES 3 - 5 ton 60 Hertz R-410A 77