Johnson Controls ZL Series Installation Manual page 72

Adjust second stage (Refer to Table 40 for input
value) pressure first, then adjust first stage (Refer to
Table 41 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.
8. If necessary, using a screwdriver, turn the first
stage adjustment screw (adjacent to the LO
marking on the valve) clockwise to increase
manifold pressure or counterclockwise to
decrease manifold pressure.
9. Once pressure has been checked, replace the
cover screws covering the HI and LO pressure
adjustment screws.
Table 41: Gas heat stages
Model Gas heat
Opt.
(size) description
Low D
ZL08
Med E
(7.5)
High F
Low D
ZL09
Med E
(8.5)
High F
Low D
ZL12 (10) Med E
High F
Low D
ZL14
Med E
(12.5)
High F
Adjustment of temperature rise
The temperature rise (the difference of temperature
between the return air and the heated air from the
furnace) must lie within the range shown on the unit
rating plate and the data in
72 Installation Manual ZL Series 7.5- 12.5 Ton 60 Hertz R-410A
1st 2nd
Total
# of burner stage stage
input
tubes input input
(Mbh)
(Mbh) (Mbh)
3 90 125 125
4 125 180 180
5 176 220 220
3 90 125 125
4 125 180 180
5 176 220 220
4 125 180 180
5 176 220 220
5 200 250 250
4 125 180 180
5 176 220 220
5 200 250 250
Physical data.
Johnson Controls Ducted Systems
After the temperature rise has been determined, the
CFM can be calculated as follows:
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
6 feet from the furnace) where they will not be
affected by radiant heat. Increase the blower CFM to
decrease the temperature rise; decrease the blower
CFM to increase the rise (See SUPPLY AIR DRIVE
ADJUSTMENT).
Note: Each gas heat exchanger size has a
minimum allowable CFM. Below this CFM, the
limit will open.
Burners/orifices inspection/servicing
About this task:
Before checking or changing burners or orifices,
CLOSE MAIN MANUAL SHUT-OFF VALVE AND SHUT
OFF ALL POWER TO THE UNIT.
1. Open the union fitting just upstream of the
unit gas valve and downstream from the main
manual shut-off valve in the gas supply line.
2. Remove the screws holding each end of the
manifold to the manifold supports.
3. Disconnect wiring to the gas valve. Remove
the manifold & gas valve assembly. Orifices
can now be inspected and/or replaced.
To service burners, complete Step 4.
4. Remove the heat shield on top of the manifold
supports. Burners are now accessible for
inspection and/or replacement.
Note: Reverse the above procedure to
replace the assemblies.
Result
Make sure that burners are level and seat at the rear
of the gas orifice.
Figure 28: Typical flame