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Table 28: Gas Heat Stages
Unit
# of Burner
Tubes
Size
Opt.
H06
4
H08
4
H12
6
037
N06
4
N08
4
N12
6
H06
4
H08
4
H12
6
049
N06
4
N08
4
N12
6
H08
4
H12
6
H16
8
061
N08
4
N12
6
N16
8
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 10.
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.
Johnson Controls Ducted Systems
2nd Stage
1st Stage
Input
Input (Mbh)
(Mbh)
60
-
80
-
120
-
45
15
56
24
84
36
60
-
80
-
120
-
45
15
56
24
84
36
80
-
120
-
160
-
56
24
84
36
112
48
1.
Open the union fitting just upstream of the unit gas valve
and downstream from the main manual shut-off valve in
Total
the gas supply line.
Input
2.
Remove the screws holding each end of the manifold to the
(Mbh)
manifold supports.
60
3.
Disconnect wiring to the gas valves and spark igniter(s).
80
Remove the manifold & gas valve assembly. Orifices can
120
now be inspected and/or replaced.
60
80
To service burners, complete step 4.
120
4.
Remove the heat shield on top of the manifold supports.
60
Burners are now accessible for inspection and/or
80
replacement.
120
60
NOTE: Reverse the above procedure to replace the
80
assemblies.
120
Make sure that burners are level and seat at the rear of the gas
80
orifice.
120
160
80
120
160
GAS
SUPPLY
PIPE
BURNER
BURNER BRACKET
Figure 29: Typical Flame
INLET
PRESSURE
TAP
INLET PRESSURE TAP
ON/OFF SWITCH
TERMINAL – C (COMMON)
TERMINAL – MP (1ST STAGE)
Figure 30: Typical Two Stage Gas Valve
HEAT EXCHANGER TUBE
BURNER FLAME
IGNITOR
HIGH & LOW GAS ADJUSTMENT
LO
HI
ON
OFF
OUTLET
PRESSURE
TAP
OR
TERMINAL – HI (2ND STAGE)
5167534-YIM-G-0518
(BLUE ONLY)
MATE-N-LOCK
CONNECTORS
MV
C
HI
OUTLET PRESSURE TAP
REGULATOR COVER SCREWS
(REG. ADJ. BENEATH THESE
SCREWS)
53
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