43
Continuous Blower Speed Selection from Thermostat
To select different continuous--blower speeds from the room
thermostat, momentarily turn off the FAN switch or push button
on the room thermostat for 1--3 seconds after the blower motor
BLWM is operating. The furnace control CPU will shift the
continuous--blower airflow from the factory setting to the next
highest CF selection airflow as shown in Fig. 39. Momentarily
turning off the FAN switch again at the thermostat will shift the
continuous--blower airflow up one more increment. If you repeat
this procedure enough, you will eventually shift the
continuous--blower airflow to the lowest CF selection as shown
in Fig. 39. The selection can be changed as many times as desired
and is stored in the memory to be automatically used following a
power interruption.
This feature is disabled when blower off delay is set for 180 sec.
HEAT PUMP
See Fig. 45--48 for thermostat connections.
When installed with a heat pump, the furnace control
automatically changes the timing sequence to avoid long blower
off times during demand defrost cycles. Whenever W/W1 is
energized along with Y1 or Y/Y2, the furnace control CPU will
transition to or bring on the blower motor BLWM at cooling
airflow, low--heat airflow, or the midrange airflow, whichever is
the lowest. The blower motor BLWM will remain on until the
main burners ignite, then shut OFF and remain OFF for 25
seconds before coming back on at heating airflow. When the
W/W1 input signal disappears, the furnace control begins a
normal inducer post--purge period while changing the blower
airflow. If Y/Y2 input is still energized, the furnace control CPU
will transition the blower motor BLWM airflow to cooling
airflow. If Y/Y2 input signal disappears and the Y1 input is still
energized, the furnace control CPU will transition the blower
motor BLWM to low--cooling airflow. If both the Y1 and Y/Y2
signals disappear at the same time, the blower motor BLWM will
remain on at low--heat airflow for the selected blower--OFF delay
period. At the end of the blower--OFF delay, the blower motor
BLWM will shut OFF unless G is still energized, in which case
the blower motor BLWM will operate at continuous blower
airflow.
COMPONENT TEST
The furnace features a component test system to help diagnose a
system problem in the case of a component failure. To initiate the
component test procedure, ensure that there are no thermostat
inputs to the control and all time delays have expired. Turn on
setup switch SW1--6 (See Fig. 33.)
NOTE
: The component test feature will not operate if the control
is receiving any thermostat signals or until all time delays have
expired.
The component test sequence is as follows:
1. The furnace control CPU turns the inducer motor IDM
ON at medium speed and keeps it ON through step c.
2. After waiting 15 seconds, the furnace control CPU turns
the hot surface igniter ON for 15 seconds, then OFF.
3. The furnace control CPU then turns the blower motor
BLWM ON at midrange airflow for 15 seconds, then OFF.
4. After shutting the blower motor BLWM OFF, the furnace
control CPU shuts the inducer motor IDM OFF.
NOTE
: The EAC terminals are energized when the blower is
operating.
After the component test is completed, 1 or more status codes (11,
25, 41, or 42) will flash. See Service Label on blower access
panel or Service/Status Code Instructions for explanation of
status codes.
NOTE
: To repeat component test, turn setup switch SW1--6 to
OFF and then back ON.
Step 6
—
Adjustments
SET GAS INPUT RATE
Furnace gas input rate on rating plate is for installations at
altitudes up to 2000 ft.
In the U.S.A., the input rating for altitudes above 2000 ft must be
reduced by 2 percent for each 1000 ft above sea level.
In Canada, the input rating must be derated by 5 percent for
altitudes of 2000 ft to 4500 ft above sea level.
Adjust manifold pressure to obtain input rate.
Furnace input rate must be within
¦
2 percent of input rate on
furnace rating plate.
1. Determine natural gas orifice size and manifold pressure
for correct input.
a. Obtain average heat value (at installed altitude) from
local gas supplier.
b. Obtain average specific gravity from local gas supplier.
c. Verify furnace model. Table 11 can only be used for
model 58UVB Furnaces.
d. Find installation altitude in Table 11.
NOTE
: For Canadian altitudes of 2000 to 4500 ft, use U.S.A.
altitudes of 2001 to 3000 ft in Table 11.
e. Find closest natural gas heat value and specific gravity
in Table 11.
f. Follow heat value and specific gravity lines to point of
intersection to find orifice size and low-- and high--heat
manifold pressure settings for proper operation.
EXAMPLE:
(0 -- 2000 ft altitude)
Heating value = 1050 Btu/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 45
Manifold pressure: 3.8--in. wc for high heat
1.6--in. wc for low heat
* Furnace is shipped with No. 45 orifices. In this
example, all main burner orifices are the correct size and
do not need to be changed to obtain proper input rate.
g. Check and verify burner orifice size in furnace.
NEVER ASSUME ORIFICE SIZE; ALWAYS
CHECK AND VERIFY.
2. Adjust manifold pressure to obtain input rate.
a. Remove burner enclosure front.
NOTE
: Manifold pressure MUST always be measured with the
burner box cover REMOVED.
b. Remove regulator seal caps that conceal adjustment
screws for low-- and high--heat gas valve regulators.
(See Fig 51.)
c. Move setup switch SW1--2 on control center to ON
position. (See Fig. 33.) This keeps furnace locked in
low--heat operation.
d. Jumper R and W/W1 thermostat connections on
control to start furnace.
e. Turn low--heat adjusting screw (3/32) hex Allen
wrench) counterclockwise (out) to decrease input rate
or clockwise (in) to increase input rate.
NOTE
: DO NOT set low--heat manifold pressure less than
1.3--in. wc or more than 1.7--in. wc for natural gas. If manifold
pressure is outside this range, change main burner orifices to
obtain manifold pressure in this range.
58U
VB
