Allied Air Enterprises A80UH2V - Manual (Page 33)

506471-01 Page 33 of 41 Issue 1034
Controls
Following is a description of the operation of some of the
controls used in this furnace. All models use one of each
control, except as noted.
Pressure Switch
The pressure switch is a normally open switch that monitors
combustion air flow. Inadequate air flow resulting from
excessive venting system restriction or a failed combustion
blower will cause the switch to remain open. A80UH2V and
80G2UHV models have two pressure switches.
Rollout Switch
The rollout switch is a normally closed switch that opens when
abnormal temperatures exist in the burner area. This can be
caused by a restricted heat exchanger causing burner flame
to “roll out” into the vestibule area or burner box.
This switch must be manually reset by pushing the button
on top to restore furnace operation. A80UH2V and
80G2UHV models have two rollout switches.
Primary Limit Control
This is a normally closed control that opens if abnormally
high circulating air temperatures occur. It is an automatic
reset control.
Auxiliary Limit Control
This is a normally closed control, located on the circulating
air blower housing, that opens under abnormal “reverse air
flow” conditions that could occur in a counterflow or horizontal
installation if the circulating air blower fails. It is an automatic
reset control.
Interlock (Blower Door) Switch
When the blower door is removed, the interlock switch
breaks the power supply to the burner controls and blower
motor. The switch operation must be checked to confirm it
is operating correctly.
Checking and Adjusting Gas Input
The minimum permissible gas supply pressure for the
purpose of input adjustment is 5"w.c. for natural gas or 11"
w..c. for propane gas. This furnace requires conversion for
use with propane (see Accessories section on page 26 for
correct kit). The maximum inlet gas supply pressure is 10.5"
w.c. for natural gas and 13" w.c. for propane. Gas input
must never exceed the value shown on the furnace rating
plate.
These units are equipped for rated input at manifold pressures
of 1.7" w.c. (1
st stage) and 3.5" w.c. (2 nd stage) for natural gas.
When these furnaces have been converted for use with
propane gas, the manifold pressures are 4.9" w.c. (1 st stage)
and 10.0" w.c. (2 nd stage).
To measure inlet or outlet pressure, remove plug from
desired pressure tap (inlet or outlet) as shown in Figure 38
and connect a water manometer or gauge to the proper
pressure tap.
These models have separate adjusting screws (3/32" hex) for
1
st stage (marked “LO”) and 2 nd stage (marked “HI”). The
adjusting screws are positioned on either side of the barbed
fitting (see Figure 38). Turn the adjusting screws clockwise to
increase pressure and input; counterclockwise to decrease
pressure and input. The pressure regulator adjustment is
sensitive; one turn of the adjusting screw will result in a relatively
large change in manifold pressure.
To adjust the regulator:
1. Set high-fire (2 nd stage) setting by turning hex adjustment
screw to desired rate.
2. Set low-fire (1 st stage) setting by turning hex adjustment
screw to desired rate.
Make sure the final high and low fire manifold pressures
are within the allowable ranges specified above for the
gas being used.
Be sure to replace the inlet and outlet pressure tap plugs
after testing and/or adjusting gas input.
Figure 38
GAS VALVE SHOWN IN “ON” POSITION
The furnace rate must be within +/- 2% of the appliance
rating input.
CAUTION