127878-YIM-C-1208
Johnson Controls Unitary Products 61
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 16.
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.
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 assem-
blies.
Make sure that burners are level and seat at the rear of the
gas orifice.
CFM Btu Input
0.8
1.08 Δ°F⋅()
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•=
FIGURE 36 : TYPICAL GAS VALVE
I N L E T
P R E S S U R E
T A P
H I G H & L O W G A S A D J U S T M E N T
O U T L E T
P R E S S U R E
T A P
M A T E - N - L O C K
C O N N E C T O R S
H I
L O
O N
O F F
M V
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