1133391-YIM-A-1014
Johnson Controls Unitary Products
55
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.
NOTE:
When using natural gas, the manifold pressure (100%
input) should be 3.5 IWG ± 0.3.
Two Stage
This gas furnace has two heat stages. Therefore, the gas valve
has two adjustment screws located under a plastic protective
cover. The second stage (100% input) adjustment screw is
adjacent to the “HI” marking on the valve and the first stage
(60% input) adjustment screw is located adjacent to the “LO”
marking on the valve (See Figure 34).
Manifold pressure adjustment procedure.
Adjust second stage (100% input) pressure first, then adjust
first stage (70% input) 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 plastic cap 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 the
second stage
adjustment screw (adjacent to the “HI” marking on the
valve) clockwise to increase manifold pressure or
counterclockwise to decrease manifold pressure.
Be sure
not to over-fire the unit on second stage
.
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.
Be sure
not to under-fire the unit on first stage
.
9.
Once pressure has been checked, replace the plastic cap
covering the HI and LO pressure adjustment screws.
NOTE:
When using natural gas, the manifold pressure for
second stage (100% input) should be 3.5 IWG ± 0.3.
The manifold pressure for first stage (70% or 75%
input) when using natural gas should be 1.5 IWG ± 0.3.
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 CSA rating plate and the data in Table 9.
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
Before checking or changing burners, pilot 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 valves and spark igniter(s).
Remove the manifold & gas valve assembly. Orifices can
now be inspected and/or replaced.
To service burners, complete step 4.
Table 27: Gas Heat Stages
Unit
# of Burner
Tubes
1st Stage
Input (Mbh)
2nd Stage
Input
(Mbh)
Total
Input
(Mbh)
Size
Opt.
037
A05
4
60
-
60
A07
4
80
-
80
A09
6
120
-
120
N05
4
45
15
60
N07
4
56
24
80
N09
6
84
36
120
049
A05
4
60
-
60
A07
4
80
-
80
A09
6
120
-
120
N05
4
45
15
60
N07
4
56
24
80
N09
6
84
36
120
061
A07
4
80
-
80
A09
6
120
-
120
A13
8
160
-
160
N07
4
56
24
80
N09
6
84
36
120
N13
8
112
48
160
