American Standard YK-IOM-2, Installation Operation & Maintenance

Page: 20 / 24

20
Power-up Initialization
The “initialization” by the Unitary Control Processor (UCP) oc-
curs each time the system is powered-up. The UCP performs
internal self-diagnostics checks, which include identifying the
equipment components of its system, and the configuring of it-
self to that system. It also checks itself to be sure it is function-
ing correctly. On units with the optional economizer, the
damper is driven open for 15-20 seconds and then fully closed
for 90 seconds. The UCP system indicator LED is turned to
“ON” within one second of start-up if operation is correct.
The Unitary Control Processor (UCP) switches are factory set
to provide comfort for most applications. Control cycles may
be adjusted as indicated in the table below. These switches
function similar to the heat anticipator adjustment in conven-
tional thermostats.
Unitary Control Processor (UCP)
Switch Settings for Cycle Timing
Switch 1 Switch 2 Cycle Time
OFF OFF
NORMAL (Factory Setting)
OFF ON
LONGER
ON OFF
SHORTER
ON ON
*SPECIAL
* Special applications, where very short cycles are
necessary to prevent excessive temperature swings.
Starting the Unit in the Heating Mode
Note: See “Sequence of operation” in the unit Service
Facts for a complete description of heating operating
sequence.
Check to ensure all grilles and registers are open and all unit
access doors are closed before start-up.
Purge the gas supply line of air by opening the union ahead of
the unit. When the odor of gas is detected, re-tighten union
and wait 5 minutes before proceeding.
Place the zone system switch in the heat position.
Postition the heating setpoint approximately 6 o C (10 o F) de-
grees above room temperature and place the fan switch in
"Auto" or "On" position.
Open the main gas valve and turn on unit main power supply.
Note: To bypass time delays, and verify the operation
of this unit from the roof, use the “Test mode
procedure” on page 3 and 4 of this manual.
The combustion blower motor and ignitor should energize.
The main burners should light within one minute from the time
the combustion blower starts. Initial start may be delayed
somewhat if unit is not purged and air is trapped in gas line.
If burners fail to ignite after 3 tries the ignition system will lock-
out. Reset by disconnecting and re-applying unit power.
Unit will start in the high fire mode. After a short run cycle it will
switch to low fire.
Note: Blue smoke produced by the heat exchanger
during the initial burner firing is caused by a thin film
of oil on the surface of the heat exchanger. This oil
will burn off quickly.
Check control operation and burner operating conditions
through the sight glass in burner assembly cover.
Manifold Pressure
Connect a manometer to the pressure tap at the outlet side of
the unit gas valve. Read the manifold pressure with the main
burners firing. The manifold pressure reading indicated should
be a (negative) -50 Pa (2 inches of water column.)
If the manifold pressure reading does not match the value indi-
cated on the unit nameplate, the unit pressure regulator must
be adjusted as follows:
Remove the cover screw on the gas regulator (located on the
top side of the unit gas valve).
Turn the adjusting screw clockwise to increase manifold pres-
sure, or counter-clockwise to decrease manifold pressure.
Open and lock unit
disconnect switch before continuing installation.
Failure to do so could result in severe personal injury
or death due to electrical shock or contact with
moving parts.
Adjust the evaporator fan motor rpm (at the motor sheave) to
a speed which most closely approximates the rpm value found
in the motor sheave/fan speed (rpm) table in the Service
Facts. To insure proper unit operation, the resulting airflow
must be or - 20 percent of the nominal airflow rate.
After adjusting the evaporator fan, check heat exchanger tem-
perature rise during furnace operation to insure that it falls
within the range specified on the unit nameplate.
If the temperature rise noted is outside of the specified limits,
adjust the fan motor sheave to cause the temperature rise of
the heat exchanger to fall within the required range.
Heating Shut-down
To exit the test mode, disconnect unit power for 3-5 seconds
and reapply. When running the unit using the zone sensor as
the control, position the selector switch at "Off". There will be a
delay of 0 - 90 seconds before the unit shuts down in this set-
ting.
Do not operate the unit
without the evaporator fan access panel in place.
Reinstall the access panel after performing any
maintenance procedures on the fan. Operating the
unit without the access panel properly installed may
result in severe personal injury or death.