Amana GUIA Series Service Instructions Manual page 93

SYSTEM OPERATION
NORMAL SEQUENCE OF OPERATION
(80% Two-Stage Variable Speed Models with White-
Rodgers 50A51-225 Integrated Ignition Control)
(90% Two-Stage Variable Speed Models with White-
Rodgers 50A51-235 Integrated Ignition Control)
Power Up
The normal power up sequence is as follows:
1. 115 VAC power applied to furnace.
2. Integrated control module performs internal checks.
3. Integrated control module flashes LED one time.
4. Integrated control module monitors safety circuits con-
tinuously.
5. Furnace awaits call from thermostat.
Heating Mode
The normal operational sequence in heating mode is as
follows:
1. R and W1 (or R and W1 and W2) thermostat contacts
close, initiating a call for heat.
2. The induced draft blower is energized on high speed for
a 10 second prepurge. Humidifier terminals are energized
with induced draft blower.
3. The induce draft blower steps down to low speed follow-
ing prepurge.
4. The ignitor is energized and is allowed to preheat for 17
seconds.
5. The gas valve is energized delivering gas to the burners
at the low stage heat flow rate.
6. The control checks for a signal from the flame sensor
within seven seconds after the gas valve is energized
(opens). Gas will only continue to flow if a signal is
present.
7. The control checks the thermostat to see whether the
call for heat is for low stage heat or high stage heat. If
the call is for high stage heat, the induced blower is
switched to high speed and the gas valve is energized
on high flow rate.
8. The control waits 30 seconds and turns on the air circu-
lator blower to the appropriate speed (high heat speed
for high heat or low heat speed for low heat). The circu-
lator blower will take 30 seconds to ramp up to full speed.
Electronic air cleaner terminals are energized with the
circulator blower.
9. The furnace is now operating on the specified stage
called out by the two-stage thermostat.
10. If the two-stage thermostat changes the call from low
heat to high heat, the control will immediately switch
the induced draft blower motor, gas valve, and air cir-
culating speed to their high stage setting.
11. If the two-stage thermostat changes the call from high
heat to low heat, the control will immediately switch the
induced draft blower motor to low speed and switch the
flow rate on the gas valve to low. The air circulator blower
will remain on high heating speed for thirty seconds be-
fore switching to the low heat circulating speed. The 30
second delay feature on the circulator speed eliminates
the possibility of tripping the high (primary) limit when
the high stage flue products are traveling through the
heat exchanger upon a call for low stage heat.
12. R and W1 (or R and W1 and W2) thermostat contacts
open, completing the call for heat.
13. The control turns the gas valve off, extingushing flame.
14. After a five second delay while flue products are purged
from the heat exchanger, the induced draft blower motor
is turned off (the induced blower is on low speed during
the five second post purge). Humidifier terminals are
de-energized.
15. The air circulator blower fan has an adjustable delay-
off timing of 60, 90, 120, or 180 seconds (starting from
the time the gas valve closes). The speeds run during
this period depend on the last heat call seen by the ther-
mostat.
If the last call for heat was a call for low heat, the air
circulator blower will run on the low heat speed for the
duration of the adjusted delay-off timing (60, 90, 120, or
180 seconds).
If the last call for heat was a call for high heat, the air
circulator blower run on the high heating speed for thirty
seconds and then switch to the low heating speed for
the balance of the adjusted delay-off timing (30, 60,
90, or 150 seconds).
Example: A GUIV090DX50 has the heating blower off
delay set to 120 seconds by the installer. When the
thermostat is satisfied after a call for high heat, the air
circulator blower will run on high speed for 30 seconds
and then switch to low circulator speed for 120 - 30 =
90 seconds.
The adjustable delay-off timing allows for more heat trans-
ferred to the conditioned space from the furnace. After
the delay time has elapsed, the air circulator blower is
de-energized. The adjustable delay-off timing feature
allows the installer to customize the comfort level based
on the predominant staging requirements of the living
space.
16. The air circulator blower will ramp down for another 30
seconds and shut down.
17. Electronic air cleaner terminals are de-energized.
18. Furnace awaits next call from thermostat.
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