Daikin FC Series, Installation And Maintenance Manual

In general, if the discs are located too far back in the blast 

tube, uneven heat distribution will result . The back of the 

exchanger will get too hot and the front will remain cool . 

Rough light off of the main flame can also result. If the discs 

are located too far forward, the widened, shortened flame will 

cause the front of the exchanger to get too hot, and the back 

will remain cool . Poor combustion can also result, as will be 

indicated by a CO test .
The gun assembly can be adjusted forward and backward by 

first loosening the three bolts on the bracket where the gas 

pipe enters the burner box . Other adjustments are made by 

tightening the pipe fittings in the gun assembly.

Modulating Linkage Adjustment

All burners are factory adjusted and test fired prior to shipment 

and therefore at most should require only minor adjustments . 

The dimensions given for linkage adjustments, etc ., are 

intended to serve as a guide when replacing components . 

It is not intended that on start-up the service technician 

will go through the burner and readjust deviations to these 

dimensions .

Procedure 

(see 

Figure 20 on page 36

):

1 . 

Adjust firing rate positioner crankarm. Side of swivel to 

edge of slot equals B .

2 .  Adjust “positioner to valve” pushrod to dimension C, 

clamp to clamp .

3 .  Adjust “valve to air damper” pushrod to dimension D .
4 .  Adjust air damper arm length to dimension E .
5 . 

With the firing rate positioner at its minimum fire position, 

tighten the air damper arm to arm damper shaft while the 

damper blade is positioned to opening F .

6 . 

 Adjust the air damper side fills for minimum gap along 

the side of the air damper blade . Do not adjust so tight 

that the blade binds or scrapes .

7 .  Adjust slide damper to dimension H .
8 .  If all these adjustments have been made to these 

specification, the air damper end opening should be F at 

the minimum fire position and G at the high fire position.

9 . 

Finally, fine tune these adjustments with instruments. 

Connect a manometer to the tap on the manifold 

to measure gas pressure at the orifice. When the 

modulating operator is positioned to the minimum fire 

position and the burner is operating, readjust C to obtain 

the specified minimum fire gas pressure on the orifice. 

Typical: 0 .44 in . W .C . natural gas . Readjust D to obtain 

an even, quiet flame and the specified CO

2

 and CO .

10 . 

Reposition modulating operator to high fire position 

and adjust the pressure regulator to specified manifold 

pressure .

Altitude Considerations

For altitudes above 2000 feet, the gas burner must be derated 

4% for every 1000 feet of altitude .
Example: An 800 MBh output furnace at an altitude of 3000 

feet is derated (0 .04 

×

 3 = 0 .12) . At 1000 MBh input (1000 

×

0 .12 = 120 MBh), the actual input is (1000 - 120 = 880 MBh) at 

3000 feet .
The method of derating the burner is to reduce the manifold 

pressure for the pilot and main burner . First, refer to 

Capacities 

and Dimensions on page 36

 . Multiply the 100% Gas 

Manifold Orifice Pressure shown under Column 10, and then 

the Pilot Gas Pressure shown under Column 7, by the following 

altitude factors:

2000 feet = 1 .0

5000 feet = 0 .774

3000 feet = 0 .922

6000 feet = 0 .706

4000 feet = 0 .846

7000 feet = 0 .64

Combustion Testing

Proper start-up and maintenance requires periodic combustion 

tests and the systematic recording of those test results for 

future reference . Before making combustion air adjustments, 

check for proper input rate .

Verify Input Rate

To determine the input rate it is necessary to know the BTU 

per cubic foot of gas being used . If this is not known, contact 

the gas supplier . Check input rate by timing the gas meter dial 

with all other appliances and their pilot lights off. If 1000 BTU/

cu. ft. gas is being used the input can be verified using 

, the 

measured manifold pressure, and checking the orifice drill 

diameter .
To verify the input rate using the gas meter, use a stopwatch 

and time one revolution of the dial . Calculate the input with the 

following formula:

MBh Input = A 

×

 B 

×

 3 .6 

 C

Where:  A = BTU/cu. ft. of gas 

Typical: Natural gas= 1000, LP gas=2500 

B = Cu. ft. per revolution of meter dial 

C = Seconds required for 1 revolution of meter dial

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