Goodman GMEC96 Service Instructions Manual page 42

SYSTEM OPERATION
CALL FOR 2ND STAGE AFTER FIRST STAGE:
. The inducer motor is enabled at high speed.
· The pressure switches are checked for closure. Clo-
sure of the second stage pressure switch will ener-
gize the high fire stage of the gas valve.
· The high speed circulator output is energized.
· NOTE: A call for 2nd stage without a call for 1st stage
will be ignored, and a three amber flash code will be
displayed on the LED. This error code will only be
stored in memory once during a single power cycle.
2ND STAGE SATISFIED, FIRST STAGE STILL
CALLED:
· When the second stage of the thermostat is satisfied,
the inducer blower is reduced to low speed which de-
energizes the second stage of the gas valve.
· After the high heat off delay expires, the circulator is
reduced to low heat speed.
SIMULTANEOUS CALL FOR LOW AND HIGH HEAT
A call for both stages of heat will establish low fire before
going to high fire
Operation Using a Single Stage Heating Thermostat
Using a single stage thermostat, the options for high fire
delay are: 10 minutes; 20 minutes; or auto
· The automatic second stage logic is a method of en-
ergizing the second stage valve based on the recent
average of the heating duty cycle. During a typical
heating day there will be at least one call for heat
within a 3 hour period, and usually much more often.
During this mode the low to high stage delay is deter-
mined by using the average calculated duty cycle from
the table below. Once the specified delay time has
expired the second stage valve will be energized
· On the heating cycle following a period of 3 hours (or
greater) in which there is no call for heat, the second
stage valve will energize based on the average calcu-
lated duty cycle prior to the three hour no call for heat.
If the average calculated duty cycle is less than 50%,
then the low to high stage delay will be determined
from the table below. In this case, an assumption is
made that the outside temperature is fairly mild and
the long time between calls for heat was due to a low
thermal loss in the building. Going quickly to second
stage heat is not required in this instance.
· If the average calculated duty cycle is 50% or greater,
then the heating cycle will be treated as if high stage
is needed and the transition from low to high stage
delay will happen quickly. In this case an assumption
is made that the outside temperature is cold and that
the thermostat is likely coming out of setback. Since
assumptions are being made during this heating cycle
the duty cycle for this heat cycle will not be used in
the average calculated duty cycle formula for future
42
heating cycles.
· The duty cycle is calculated every cycle and used
during the next cycle. The equation for the duty cycle
is calculated as follows: Duty Cycle = (Time the ap-
propriate stage is ON) / (Time of the complete cycle).
· The average calculated duty cycle is determined by
averaging the previous average calculated duty cycle
with the duty cycle from the previous cycle. This places
a large emphasis on the previous cycle but allows a
large variation in any one duty cycle to be averaged
out after just a few complete heating cycles.
· If there is no load activity for 24 hours or more then
set the Duty Cycle = 100%
· The initial default average calculated duty cycle =
50%
Duty Cycle % Valve Output
0-38 1 Stage, 12 minute 2
st
38-50 1 Stage, 10 minute 2
st
50-62 1 Stage, 7 minute 2
st
62-75 1 Stage, 5 minute 2
st
75-88 1 Stage, 3 minute 2
st
88-100 1 Stage, 1 minute 2
st
Blower Off Delay Dip Switches
Purpose Switch Group Function
Heating Fan Off
S1
Delay
Blower Off Delay Dip Switches
Purpose Switch Group Function
Heating Fan Off
S3
Delay
*Factory Setting
Heat Mode Blower Off Delay Timing
COOLING MODE:
LOW STAGE COOLING MODE SEQUENCE:
· On a call for lo cool, the Ylo and G thermostat con-
tacts close signaling the control module.
· The LED will display a "GREEN"1 flash
· The compressor and condenser fan are energized. The
compressor is connected to the Ylo terminal of the
control module.
Demand
Stage Light
nd
Stage Light to Average
nd
Stage Average
nd
Stage Average to Heavy
nd
Stage Heavy
nd
Stage Heavy
nd
PCBBF137
Dip Switch
1 2 3
90 OFF
120 OFF
150 ON*
180 ON
PCBBF139
Dip Switch
1 2 3
90 OFF
120 OFF
150 ON*
180 ON
4
OFF
ON
OFF*
ON
4
OFF
ON
OFF*
ON