335224-BIM-B-1208
Johnson Controls Unitary Products
59
2.
Check for correct manifold gas pressures. (See ’CHECK-
ING GAS INPUT’.)
3.
Check the supply gas pressure. It must be within the lim-
its shown on the rating nameplate. Supply pressure
should be checked with all gas appliances in the building
at full fire. At no time should the standby gas pressure
exceed 10.5 in. or the operating pressure drop below 4.5
in for natural gas units. If gas pressure is outside these
limits, contact the local gas utility or propane supplier for
corrective action.
SHUT DOWN
1.
Set the thermostat to the lowest temperature setting.
2.
Turn “OFF” all electric power to unit.
3.
Open gas heat access panel.
4.
Turn gas valve clockwise to “OFF” position (See Figure
36).
MANIFOLD GAS PRESSURE ADJUSTMENT
This gas furnace has two heat stages. Therefore, the gas
valve has two adjustment screws located under a plastic pro-
tective 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 36).
Manifold pressure adjustment procedure.
Adjust second stage (100% input) pressure first, then adjust
first stage (60% 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 adjust-
ment screws.
4.
Turn on power to the unit.
5.
Set thermostat to call for second stage heat and start fur-
nace.
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 coun-
terclockwise 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 (60%
input) when using natural gas should be 1.5 IWG ±
0.3.
CHECKING GAS INPUT
NATURAL GAS
This unit has two stages of gas heat. The first stage is 60% of
the full fire input and is considered the minimum input for the
furnace. The intended input for each furnace is shown in the
table below. The following Table applies to units operating on
60 Hz power only.
To determine the rate of gas flow (Second Stage).
1.
Turn off all other gas appliances connected to the gas
meter.
2.
Turn on the furnace and make sure the thermostat is
calling for Second stage (100% input) heat.
3.
Measure the time needed for one revolution of the hand
on the smallest dial on the meter. A typical gas meter
has a 1/2 or a 1 cubic foot test dial.
FIRE OR EXPLOSION HAZARD
Failure to follow the safety warning exactly could
result in serious injury, death or property damage.
Never test for gas leaks with an open flame. use a
commercially available soap solution made specifi-
cally for the detection of leaks to check all connec-
tions. A fire or explosion may result causing property
damage, personal injury or loss of life.
TABLE 39: GAS HEAT STAGES
# of Burner Tubes
2nd Stage
Input (100%
Btuh)
1st Stage
Input (60%
Btuh)
4
120,000
72,000
6
180,000
108,000
8
240,000
144,000
