Allied A80US2V User manual

508155-01 Issue 2108 Page 1 of 49
SERVICE MANUAL
A80US2V Gas Furnace
(P) 508155-01
*P508155-01*
Table of Contents
Technical Specications - A80US2V............................2
Parts Arrangement.......................................................5
Unit Components.........................................................6
Placement and Installation ........................................27
Start-Up .....................................................................27
Heating System Service Checks ...............................28
Typical Operating Characteristics..............................31
Maintenance..............................................................32
Wiring and Sequence of Operation ...........................35
Field Wiring Applications with Conventional Thermostat
...................................................................................40
Program Unit Capacity Size Modes...........................44
Troubleshooting: Heating Sequence of Operation ....45
Troubleshooting: Cooling Sequence of Operation.....48
Troubleshooting: Continuous Fan Sequence of
Operation...................................................................49
This is a safety alert symbol and should never be ignored. When you see this symbol on labels or in manuals, be alert to
the potential for personal injury or death.
Electric shock hazard.
Can cause injury or death. Before attempting
to perform any service or maintenance,
turn the electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.
WARNING
As with any mechanical equipment, contact with sharp
sheet metal edges can result in personal injury. Take
care while handling this equipment and wear gloves
and protective clothing.
CAUTION
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional HVAC installer (or
equivalent), service agency or the gas supplier.
WARNING

508155-01Issue 2108Page 2 of 49
Technical Specications - A80US2V
MODEL NUMBER GUIDE
PHYSICAL AND ELECTRICAL DATA
Model Input
(Btuh) Output* (Btuh) AFUE (ICS)
Nominal
Cooling
Capacity
Gas
Inlet
(in.)
Volts/
Hz/
Phase
Max. Time
Delay
Breaker or
Fuse
Nominal
F.L.A. Trans. (V.A.)
Approx.
Shipping
Weight
(lbs.)
UPFLOW/HORIZONTAL
A80US2V070A12 66,000 52,000 80.0% 3 tons 1/2 120-60-1 15 7.7 40 128
A80US2V090B12 88,000 70,000 80.0% 3 tons 1/2 120-60-1 15 7.7 40 143
A80US2V090B16 88,000 70,000 80.0% 4 tons 1/2 120-60-1 20 12.8 40 154
A80US2V090C20 88,000 70,000 80.0% 5 tons 1/2 120-60-1 20 12.8 40 173
A80US2V110C20 110,000 87,000 80.0% 5 tons 1/2 120-60-1 20 12.8 40 181
A80US2V135D20 132,000 105,000 80.0% 5 tons 1/2 120-60-1 20 12.8 40 199
A80US2V070A12L 66,000 52,000 80.0% 3 tons 1/2 120-60-1 15 7.7 40 128
A80US2V090B16L 88,000 70,000 80.0% 4 tons 1/2 120-60-1 20 12.8 40 154
A80US2V110C20L 110,000 87,000 80.0% 5 tons 1/2 120-60-1 20 12.8 40 181
Note: For vent length and clearances to combustibles, please reference installation instructions.
* Outputs shown are High Fire, 100% rate, Low Fire is 67% of shown output.
Major Revision Code
Numeric Code
Option Code
L = Low NOx
Nom. CFM x 100
8 = 3 Ton add on cooling
12 = 3 Ton add on cooling
16 = 4 Ton add on cooling
20 = 5 Ton add on cooling
Cabinet Width
A = 14.5" WIDTH
B = 17.5” width
C = 21.0” width
D = 24.5” width
A = Flagship
AFUE
80 = 80% Efficency
Configuration
U = Upflow/Horizontal
D = Downflow
S = Communicating
Stages
2 = Two Stage
V = Variable Speed
BTUH Width
Heating Input x 1000
A 80 U S 2 V 110 C 20 L - 01

508155-01 Issue 2108 Page 3 of 49
BLOWER PERFORMANCE DATA
Model
Motor
Size
(hp)
Blower
Size
Heating Cooling
Low Fire High Fire Cooling
Stage Speed Adjustment
CFM @ 0" - 0.8" w.c.
Rise
Range
Fº
Speed
Adjustment
CFM @
0" - 0.5"
w.c.
Rise
Range
Fº
Speed
Adjustment
CFM @
0" - 0.5"
w.c. Low Med Low Med High High
(Default)
Upow/Horizonatl
A80US2V070A12(L)
1/2 HP 10 x 8 25-55
+24% 1073
40 -70
+24% 1178
1st Stage
+10% 748 801 864 970
+18% 1021 +18% 1121 Default 680 728 785 882
+12% 969 +12% 1064
+6% 917 +6% 1007 -10% 612 655 707 974
Default 865 Default 950
2nd Stage
+10% 1007 1095 1210 1348
-6% 813 -6% 893 Default 915 995 1100 1225
-12% 761 -12% 836
-18% 709 -18% 779 -10% 824 896 990 1103
A80US2V090B12
1/2 HP 10 x 9 25-55
+24% 1302
40 -70
+24% 1426
1st Stage
+10% 556 699 787 919
+18% 1239 +18% 1357 Default 505 635 715 835
+12% 1176 +12% 1288
+6% 1113 +6% 1219 -10% 455 572 644 752
Default 1050 Default 1150
2nd Stage
+10% 930 1100 1210 1320
-6% 987 -6% 1081 Default 845 1000 1100 1200
-12% 924 -12% 1012
-18% 861 -18% 943 -10% 761 900 990 1080
A80US2V090B16(L)
1 HP 11-1/2 x 9 25-55
+24% 1353
40-70
+24% 1488
1st Stage
+10% 743 935 1073 1238
+18% 1287 +18% 1416 Default 675 850 975 1125
+12% 1222 +12% 1344
+6% 1156 +6% 1272 -10% 608 765 878 1013
Default 1091 Default 1200
2nd Stage
+10% 1045 1320 1540 1760
-6% 1026 -6% 1128 Default 950 1200 1400 1600
-12% 960 -12% 1056
-18% 895 -18% 984 -10% 855 1080 1260 1440
A80US2V090C20
1 HP 11-1/2 x 10 25-55
+24% 1353
35-65
+24% 1488
1st Stage
+10% 897 1045 1177 1353
+18% 1287 +18% 1416 Default 815 950 1070 1230
+12% 1222 +12% 1344
+6% 1156 +6% 1272 -10% 734 855 963 1107
Default 1091 Default 1200
2nd Stage
+10% 1276 1491 1683 1931
-6% 1026 -6% 1128 Default 1160 1355 1530 1755
-12% 960 -12% 1056
-18% 895 -18% 984 -10% 1044 1220 1377 1580
A80US2V110C20(L)
1 HP 11-1/2 x 10 25-55
+24% 1693
35-65
+24% 1860
1st Stage
+10% 1155 1210 1342 1419
+18% 1611 +18% 1770 Default 1050 1100 1220 1290
+12% 1529 +12% 1680
+6% 1447 +6% 1590 -10% 945 990 1098 1161
Default 1365 Default 1500
2nd Stage
+10% 1650 1735 1914 2024
-6% 1283 -6% 1410 Default 1500 1575 1840 1840
-12% 1201 -12% 1320
-18% 1119 -18% 1230 -10% 1350 1418 1566 1656
A80US2V135D20
1 HP 11-1/2 x 11 25-55
+24% 1872
40-70
+24% 2058
1st Stage
+10% 1062 1139 1309 1419
+18% 1782 +18% 1959 Default 965 1035 1190 1290
+12% 1691 +12% 1859
+6% 1601 +6% 1760 -10% 869 932 1071 1161
Default 1510 Default 1660
2nd Stage
+10% 1513 1623 1870 2024
-6% 1419 -6% 1560 Default 1375 1475 1700 1840
-12% 1329 -12% 1461
-18% 1238 -18% 1361 -10% 1238 1328 1530 1656

508155-01Issue 2108Page 4 of 49
ACCESSORY LIST
Catalog Number Description
External Filter Rack Kits
1.841018 1 pack (16 x 25)
1.841039 10 pack (16 x 25)
Natural to LP Kits
11K48 Two-Stage (0 - 7500 ft.)
11K47 Two-Stage (>7500 ft.)
Return Air Base
68W61 Return Air Base 14.5 Inch, A Width
68W62 Return Air Base 17.5 Inch, B Width
68W63 Return Air Base 21.0 Inch, C Width
Night Service Kit
89W54 Two-Stage
Horizontal Suspension Kit
51W10 80% & 90% Kit
Combustible Floor Base
11M59 14.5 Inch, A Width
11M60 17.5 Inch, B Width
11M61 21.0 Inch, C Width
Comfort Sync®Controls
1.841226 Comfort Sync® A3 Thermostat
1.851399 Comfort Sync® Zoning Controller
1.851422 Comfort Sync® Zone Sensor
Note: For vent length and clearances to combustibles, please reference installation instructions.

508155-01 Issue 2108 Page 5 of 49
Parts Arrangement
Figure 1. Expanded View
Blower Assembly
Burner
Access Panel
Burner Box
Gas
Valve
Combustion Air Inducer
Pressure Switch
Combustion Air
Inducer
Heat
Exchanger
Cabinet
Blower
Access
Panel
Control Box
(Includes Integrated Control,
and Transformer)
Rollout Located
Inside Burner Box

508155-01Issue 2108Page 6 of 49
Unit Components
A80US2V unit components are shown in Figure 1.
The gas valve, combustion air inducer and burners can
be accessed by removing the access panel. Electrical
components are in the control box (Figure 2) found in the
blower compartment.
A80US2V units are factory-equipped with a bottom return
air panel in place. The panel is designed to be eld removed
as required for bottom air return. Markings are provided for
side return air and may be cut out in the eld.
Electrostatic discharge can a󰀨ect
electronic components. Take
precautions to neutralize electrostatic
charge by touching your hand and
tools to metal prior to handling the
control.
CAUTION
Control Box
Control Transformer (T1)
A transformer located in the control box provides power
to the low voltage section of the unit. Transformers on all
models are rated 40VA with a 120V primary and a 24V
secondary.
Transformer
Integrated Control
Interlock Switch
Circuit Breaker
Figure 2. Control Box
Door Interlock Switch (S51)
A door interlock switch rated 14A at 125VAC is wired in
series with line voltage. When the inner blower access
panel is removed the unit will shut down.
Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box. The
switch provides overcurrent protection to the transformer
(T1). The breaker is rated 3A at 32V. If the current exceeds
this limit the breaker will trip and all unit operation will
shutdown. The breaker can be manually reset by pressing
the button on the face. See Figure 3.
PRESS TO RESET
Figure 3. Circuit Breaker CB8
Shock hazard.
Disconnect power before servicing. Integrated control
is not eld repairable. If control is inoperable, simply
replace entire control.
Can cause injury or death. Unsafe operation will result
if repair is attempted.
WARNING
Integrated Control (A92)
Units are equipped with a variable capacity integrated
control. This control is used with the Comfort Sync®
thermostat as part of a communicating comfort system.
The control can also operate with a non-communicating
conventional single or two-stage thermostat. The system
consists of an ignition / blower control (Figure 4 and Figure
5) with control pin designations (Table 1 through Table 3)
and an ignitor. The control and ignitor work in combination
to ensure furnace ignition and ignitor durability. The
control provides gas ignition, safety checks and indoor
blower control with two-stage gas heating. The furnace
combustion air inducer, gas valve and indoor blower are
controlled in response to various system inputs such as
thermostat signal, pressure and limit switch signal and
ame signal. The control features a seven-segment LED
display, indicating furnace status (including indoor blower)
and error codes. The LED ashes in single digits. For
example, using Table 5 under CODE, an “E” followed by
“2” followed by “5” followed by “0”, the limit switch circuit
is open. The control also has two unpowered (dry) 1/4”
contacts for a humidier and a 120 volt accessory terminal.
Both rated at (1) one amp each.

508155-01 Issue 2108 Page 7 of 49
Pin # Function
1Ignitor
2 Combustion Air Inducer High Speed
3Combustion Air Inducer Low Speed
4Combustion Air Inducer Neutral
5Ignitor Neutral
Table 1. Control 5-Pin Terminal Designation
Pin # Function
1Gas Valve Second Stage
2 Second Stage Prove Switch
3Rollout Switch In
4Ground
524V Hot
6Primary Limit In
7 Gas Valve First Stage
8Gas Valve Common
924V Neutral
10 Ground
11 Rollout Switch Out
12 First Stage Prove Switch
Table 2. Control 12-Pin Terminal Designation
Pin # Function
1Data Input From Motor
2 Common
3Not Used
4Data Output To Motor
55 Volt Bias Supply
6Not Used
Table 3. Control 6-Pin Terminal Designation
Electronic Ignition
At the beginning of the heat cycle the integrated control
monitors the rst stage and second stage combustion air
inducer prove switch. The control will not begin the heating
cycle if the rst stage prove switch is closed (by-passed).
Likewise the integrated control will not begin the second
stage heating cycle if the second stage prove switch is
closed, and will remain in rst stage heat. However, if the
second stage prove switch closes during the rst stage
heat pre-purge, the control will allow second stage heat.
Once the rst stage prove switch is determined to be open,
the combustion air inducer is energized on low (rst stage)
heat speed. When the di󰀨erential in the prove switch is
great enough, the prove switch closes and a 15-second
pre-purge begins.
NOTE: During abnormal conditions such as low supply
voltage or low outdoor temperatures and the low re
pressure switch does not close, the combustion air inducer
will switch to high re. After a 15 second pre-purge the
high re pressure switch will close and the unit will begin
operation on high re. After 10 to 20 seconds of high re
operation the unit will switch to low re
After the 15-second pre-purge period, the ignitor warms
up for 20 seconds after which the gas valve opens for a
4-second trial for ignition. The ignitor remains energized
during the trial until ame is sensed. If ignition is not proved
during the 4-second period, the control will try four more
times with an inter purge and warm-up time between trials
of 35 seconds. After a total of ve trials for ignition (including
the initial trial), the control goes into Watchguard-Flame
Failure mode. After a 60-minute reset period, the control
will begin the ignition sequence again.
Two Stage Operation / Thermostat Selection
DIP Switch
The control can be utilized in two modes: SINGLE-STAGE
thermostat or TWO-STAGE thermostat. The thermostat
selection is made using a DIP switch and must be positioned
for the particular application. DIP switch 1, labeled T”STAT
HEAT STAGE is factory-set in the OFF position for use
with a two-stage thermostat. Move the DIP switch to ON
for use with a single stage thermostat.
While in the single-stage thermostat mode, the burners will
always re on rst-stage heat. The combustion air inducer
will operate on low speed and indoor blower will operate on
low heat speed. The unit will switch to second stage heat
after a “recognition period”. DIP switch 2, labeled SECOND
STAGE DELAY, is factory set in the OFF position for a 7
minute recognition period. The switch can be moved to the
ON position for a 12 minute recognition period, after which
time the unit will switch to secondstage heat.
While in the two-stage thermostat mode, the burners will
re on rst-stage heat. The combustion air inducer will
operate on low speed and indoor blower will operate on low
heat speed. The unit will switch to second-stage heat on
call from the indoor thermostat. If there is a simultaneous
call for rst and second stage heat, the unit will re an
rst stage heat and switch to second stage heat after 30
seconds of operation. See Sequence of Operation ow
charts in the back of this manual for more detail.

508155-01Issue 2108Page 8 of 49
Figure 4. Integrated Control

508155-01 Issue 2108 Page 9 of 49
HEATING BLOWER−OFF DELAY
60 SECOND
HTG BLOWER
OFF DELAY
120 SECOND
HTG BLOWER
OFF DELAY
180 SECOND
HTG BLOWER
OFF DELAY
FLAME
15
HSI/CAI
2ND STAGE HEAT ON DELAY
7 MIN
UPSTAGE
DELAY
12 MIN
UPSTAGE
DELAY
*CONTINUOUS FAN MODE BLOWER SPEED
COOLING MODE BLOWER RAMPING
CLG BLOWER SPEED ADJUSTMENT
COOLING MODE BLOWER SPEED
W915
2 STAGE
COMPR
1−STG COMPRESSOR
2−STAGE
COMPRESSOR LINK
(JUMPERS Y1 to Y2)
W915
DO NOT CUT
2−STG COMPRESSOR
HEAT PUMP LINK
(JUMPERS R to O)
W951
DEHUMIDIFICATION−
HARMONY LINK
(JUMPERS R to DS)
W914
W915
2 STAGE
COMPR
CUT LINK
A/C UNIT
DO NOT CUT
HEAT PUMP UNIT
CUT LINK
W951
HEAT
PUMP
W951
HEAT
PUMP
W914
DEHUM
ZONING
OR
NO SIGNATURESTAT
W/ DS CONNECTION
DO NOT CUT
ZONING
OR
SIGNATURESTAT W/
DS CONNECTION
CUT LINK
W914
DEHUM
1
1
1
ON−BOARD LINK
OPTION SELECTION
1234567
1234567
123567
4
123567
4
NEUTRALS
L1
ACC
HUM
14
36
P79
110
312
J2
4 7
W915
2 STAGE
COMPR
W951
HEAT
PUMP
W914
DEHUM
HARMONY
CUT FOR
OPTION
SELECTION
OUTDOOR
SENSOR
DISCHARGE
AIR SENSOR
123456
10 12
91113
ON
ON
W1W2 GY2 Y1 CC DHLODSR
W1 W2
G
Y2
Y1
C C
R
L
DH
HIGH
SPEED
(100%)
MEDIUM−HIGH
SPEED
(70%)
MEDIUM−LOW
SPEED
(38%)
LOW
SPEED
(28%)
*
OPTION A
OFF−50%−82%−
100%−50%−OFF
OPTION B
OFF−82%−100%−OFF
OPTION C
OFF−100%−100%−OFF
OPTION D
OFF−100%−OFF
*
DEFAULT
+ 10%
− 10%
*
HIGH
SPEED
MEDIUM−HIGH
SPEED
MEDIUM−LOW
SPEED
LOW
SPEED
*
7
−PROTECTIVE PLASTIC FILM ON DIP SWITCHES MAY BE
REMOVED FOR EASE IN SETTING OF DIP SW.
−CUT ON−BOARD LINK (SOLDER TRACE) COMPLETELY THROUGH
BOTH LAYERS ON THE CONTROL BOARD
−LINKS CUT IN ERROR −INSTALL A JUMPER ON THE APPROPRIATE
TERMINALS ON THE TERMINAL STRIP
1
910 11 12 13 14
ON
ON
ON
ON
ON
ON
ON
ON
90 SECOND
HTG BLOWER
OFF DELAY
*1234567
ON
1234567
ON
THERMOSTAT SELECTION
1−STAGE
THERMOSTAT
(TIMED STAGING)
−SEE SW #2
TWO STAGE
THERMOSTAT
*1234567
1234567
ON
ON
−BLOWER ON DELAY − 30 SEC. FIXED
15
910 11 12 14 15
910 11 12 14 15
910 11 12 14 15
8
8
8
8
8
8
8
81234567
1234567
ON
ON
1234567
ON
1234567
ON
8
8
8
8
910 11 12 13 14
ON
ON
ON
ON
15
910 11 12 14 15
910 11 12 14 15
910 11 12 14 15
910 11 12 13 14
ON
ON
ON
ON
15
910 11 12 14 15
910 11 12 14 15
910 11 12 14 15
HEATING MODE BLOWER SPEED
1234567
ON
1234567
ON
1234567
ON
8
8
8
910 11 12 13 14
ON
ON
ON
ON
15
910 11 12 14 15
910 11 12 14 15
910 11 12 14 15
FACTORY
DEFAULT
+ 24%
+ 18%
+ 12%
+ 6%
− 6%
− 12%
− 18%
8
14 15
INCREASE AIR HTG CFM
DECREASE AIR HTG CFM
SENSE
RI+ I− CR
I+ I− C
OUTDOOR EQUIPMENT
I+ I−
INDOOR EQUIPMENT
IGN
CAI2
CAI1
N N
J3
S1
S4S3
13
13
13
13
13
13
13
* FACTORY DEFAULT
13
13
*
DIAGNOSTIC
LED
DIAGNOSTIC
PUSH BUTTON
Figure 5. Integrated Control Conguration Guide

508155-01Issue 2108Page 10 of 49
Display Action (when button released)
No change (idle)* Remain in idle mode
Solid “E” Enter diagnostic recall mode
Solid “D” Discharge air installed
Solid “F” Enter ame signal mode
Solid “P” (variable speed only) Program unit capacity/size unit (Unit Code)
* No change implies the display will continue to show whatever is currently being displayed for normal operation (blinking decimal,
active error code, heat state, etc.)
Table 4. Integrated Control Diagnostic Modes
Diagnostic LED (Figure 4)
The seven-segment diagnostic LED displays operating
status, target airow, error codes and other information.
Table 5 lists diagnostic LED codes.
Diagnostic Push Button (Figure 4)
The diagnostic push button is located adjacent to the
seven-segment diagnostic LED. This button is used to
enable the Error Code Recall “E” mode, the Flame Signal
“F” mode and “P” the Program Unit Capacity/Size mode.
Press the button and hold it to cycle through a menu of
options. Every ve seconds a new menu item will be
displayed. When the button is released, the displayed item
will be selected. Once all items in the menu have been
displayed, the menu resumes from the beginning until the
button is released.
Error Code Recall Mode
Select ”E” from the menu to access the most recent 10
error codes. Select “c” from the Error Code Recall menu
to clear all error codes. Button must be pressed a second
time while “c” is ashing to conrm command to delete
codes. Press the button until a solid “≡” is displayed to exit
the Error Code Recall mode.
Flame Signal Mode
Select ”F” from the menu to access the ame signal mode.
The integrated control will display the ame current on
seven-segment LED in in micro amps (uA).
Flame signal mode is exited after any of the following:
• Power is reset
• Pressing and holding push button until 3 horizontal
lines “≡” are displayed
• 10 minutes after entering the ame sense mode.
Program Unit Capacity/Size Mode
After the “P” is selected (by releasing the push button)
the integrated control will start ashing the “P” on display
for 90 seconds. If push button is pressed again and held
during that time, the control will start to display characters
corresponding to di󰀨erent variable speed furnace models
for 3 seconds each. While the wanted character-model is
displayed push button has to be released. Selected option
will ash display for 10 seconds and during that time push
button has to be pressed and held for 5 seconds. Once
control accepts new setting it will store data in non-volatile
memory and reset itself. If 10 seconds expires or push
button is held less than 5 seconds, control will exit eld
test mode and go into idle without changing programming
the unit size.

508155-01 Issue 2108 Page 11 of 49
Code Diagnostic Codes / Status of Equipment Action Required to Clear and Recover
•Idle mode (Decimal blinks at 1 Hertz - 0.5
seconds ON, 0.5 seconds OFF).
ACubic feet per minute (cfm) setting for indoor blower (1 second ON, 0.5 seconds OFF) / cfm
setting for current mode displayed.
CCooling stage (1 second ON, 0.5 seconds OFF) / 1 or 2 displayed / Pause / cfm setting displayed /
Pause / Repeat codes.
d
Dehumidication mode (1 second ON, 1 second
OFF) / cfm setting displayed / Pause / Repeat
codes.
hHeat pump stage (1 second ON, 0.5 seconds OFF) / % of input rate displayed / Pause / cfm
setting / Pause / Repeat codes.
HGas Heat stage (1 second ON, 0.5 seconds OFF)
/ 1 or 2 displayed / Pause / cfm setting displayed /
Pause / Repeat codes. Blinking during ignition.
dF Defrost mode.
UDischarge Air Temperature
E105 Device communication problem - No other
devices on RS BUS (Communication system).
Equipment is unable to communicate. Indicates numerous message
errors. In most cases, errors are related to electrical noise. Make sure
high voltage power is separated from RSBus. Check for mis-wired and/or
loose connections between the stat, indoor unit, and outdoor unit. Check
for a high voltage source of noise close to the system. Fault clears after
communication is restored.
E110 Low line voltage. Line Voltage low (Voltage tower than nameplate rating). Check power line
voltage and correct. Alarm clears 5 seconds after fault recovered.
E113 High line voltage. Line Voltage high (Voltage higher than nameplate rating). Provide
power voltage within proper range. System resumes normal operation 5
seconds after fault recovered.
E114 Line voltage frequency out-of-range. No 60 Hertz power. Check voltage and line power frequency. Correct
voltage and frequency problems. System resumes normal operation 5
seconds after fault recovered.
E115 Low 24V - Control will restart if the error recovers. 24 Volt Power high (Range is 18 to 30 Volts). Check and correct voltage.
Check for additional power robbing equipment connected to system. May
require installation of larger VA transformer to be installed in furnace/air
handler. Clears after fault recovered.
E120 Unresponsive device (Communicating systems
only).
Usually caused by delay in outdoor unit responding to indoor unit poling.
Recycle power. Check all wiring connections. Cleared after unresponsive
device responds to any inquiry.
E124 Active communicating thermostat signal missing
for more than 3 minutes (Communicating systems
only).
Equipment lost communication with the thermostat. Check four wiring
connections, ohm wires, and cycle power at the thermostat. Alert stops
all services and waits for heartbeat message from thermostat (subnet
controller). Cleared after valid thermostat (subnet) message is received.
E125 Control failed self-check, internal error, failed
hardware. Will restart if error recovers, Integrated
control not communicating Covers hardware
errors (ame sense circuit faults, pin shorts, etc).
Hardware problem on the control. Cycle power on control. Replace if
problem prevents service and is persistent. Cleared 300 seconds after
fault recovered.
E126 Control internal communication problem. Hardware problem on the control. Cycle power on control. Replace if
problem prevents service and is persistent. Cleared 300 seconds after
fault recovered.
E131 Corrupted control parameters (Verify
conguration of system) (Communicating systems
only).
Recongure the system. Replace control if heating or cooling is not
available. Only applicable in the communicating mode not in startup. Exit
from Commissioning and Execute Se+ factory Default mode. Control will
still operate on default parameter settings.
Table 5. Integrated Diagnostic Codes/Status of Equipment

508155-01Issue 2108Page 12 of 49
Code Diagnostic Codes / Status of Equipment Action Required to Clear and Recover
E180 Outdoor air temperature sensor failure. Only
shown if shorted or out of range (Communicating
systems only)
Compare outdoor sensor resistance to temperature resistance charts
in unit installation instructions. Replace sensor pack if necessary. At
beginning of (any) conguration, furnace or air handler control will sense
outdoor air and discharge air temperature sensor(s) If detected (reading
in range), appropriate feature will be set as installed and that could be
seen in 'About ' screen. In normal operation after control recognizes
sensors, alarm will be sent if valid temperature reading is lost. To get rid
of setting and alarm, redo conguration and make sure that temperature
sensor is marked as not installed in indoor Unit ‘About’ screen. When
indoor unit control is replaced thermostat will ‘tell’ new control if
temperature sensor is in system or not. Clears 30 seconds after fault
recovered.
E200 Hard Lock out - Rollout circuit open or previously
open Correct cause of rollout trip or replace ame rollout switch. Test furnace operation. Cleared after fault recovered.
E201 Indoor blower/communication failure - Unable to
communicate with blower motor
Indoor blower communication failure including power outage. Lost
communication with indoor blower motor. Possible causes: motor not
powered, loose wiring. Problem may be on control or motor side. Cleared
after fault recovered.
E202 Indoor blower motor mis-match - indoor motor
horsepower does not match unit capacity
Incorrect appliance capacity code selected. Check for proper conguring
under Unit Size Code for Furnace/Air Handler on conguration guide or
in installation instructions. Cleared after the correct match is detected
following a reset. (Remove thermostat from system while applying power
and reprogramming)
E203 Appliance capacity size is NOT programmed.
Invalid unit codes. Refer to conguration ow
chart.
No appliance capacity code selected. Check for proper conguring under
Unit Size Codes for Furnace on conguration guide or in installation
instruction. Critical Alert Cleared after valid unit code is read following
a reset (remove thermostat from system while applying power and
reprogramming)
E204 Gas valve mis-wired Check gas valve operation and wiring. Clears when repaired.
E205 Gas valve control relay contact shorted Check wiring on control and gas valve. If wiring is correct replace control.
E207 Hot surface igniter sensed open - Refer to
troubleshooting
Measure resistance of hot surface igniter. Replace if open or not within
specied range found in 10M. Resumes normal operation after fault is
cleared.
E223 Low pressure switch failed open Check pressure(inches W.C) of low pressure switch closing on heat call.
Measure operating pressure (inches w.c.). Inspect vent and combustion
air inducer for correct operation and restriction. Resumes normal
operation after fault is cleared.
E224 Low pressure switch failed closed -Refer to
troubleshooting
Check pressure(inches W.C) of low pressure switch closing on heat call.
Measure operating pressure (inches w.c.). Inspect vent and combustion
air inducer for correct operation and restriction. Resumes normal
operation after fault is cleared.
E225 High pressure switch failed open -Refer to
troubleshooting
Check pressure(inches W.C) of high pressure switch closing on heat call.
Measure operating pressure (inches w.c. Inspect vent and combustion air
inducer for correct operation and restriction Resumes normal operation
after fault is cleared.
E226 High pressure switch failed closed -Refer to
troubleshooting
Check operation of high pressure closing on heat call. Measure operating
pressure (inches w.c.). Inspect vent and combustion air inducer for
correct operation and restriction. Resumes normal operation after fault is
cleared.
E227 Low pressure switch open during trial for ignition
or run mode. Refer to troubleshooting
Check operation of low pressure switch closing on heat call. Measure
operating pressure (inches w.c.). Inspect vent and combustion air inducer
for correct operation and restriction. Resumes normal operation after fault
is cleared.
E228 Combustion air inducer calibration failure Unable to perform pressure switch calibration. Check vent system and
pressure switch wiring connections. Resumes normal operation after fault
is cleared.
Table 5. Integrated Diagnostic Codes/Status of Equipment

508155-01 Issue 2108 Page 13 of 49
Code Diagnostic Codes / Status of Equipment Action Required to Clear and Recover
E240 Low ame current - Run mode- Refer to
troubleshooting
Check micro-amperes of ame sensor using control diagnostics or eld
installed mode. Clean or replace sensor. Measure voltage of neutral to
ground to ensure good unit ground. Alert clears after current heat all has
been completed.
E241 Flame sensed out of sequence-Flame still
present.
Shut o󰀨 gas. Check for gas valve leak. Replace if necessary. Alert clears
when fault is recovered.
E250 Limit switch circuit open - Refer to
troubleshooting.
Check for proper ring rate on furnace. Ensure there is no blockage in
heater. Check for proper air ow. If limit not closed within 3 minutes unit
will go into 1 hour soft lockout. Resumes normal operation after fault is
cleared.
E252 Discharge air temperature too high (gas heat
only).
Check temperature rise airow and input rate. Clear when heat call is
nished.
E270 Soft lockout - Exceeded maximum number of
retries. No ame current sensed.
Check for proper gas ow. Ensure that igniter is lighting burners. Check
ame sensor current. Clears when heat call nishes successfully.
E271 Soft lockout - Exceeded maximum number of
retries. Last retry failed due to the pressure switch
opening.
Check pressure (inches w.c.) of low pressure switch closing on heat call.
Measure operating pressure (inches w.c.). Inspect vent and combustion
air inducer for correct operation and restriction. Clears when heat call
nishes successfully.
E272 Soft lockout - Exceeded maximum number of
recycles. Last recycle due to the pressure switch
opening
Check operation of low pressure to see if it is stuck closed on heat call.
Check pressure (inches w.c.) of high pressure switch closing on heat call.
Measure operating pressure. Inspect vent and combustion air inducer
for correct operation and restriction. Clears when heat call nishes
successfully.
E273 Soft lockout - Exceeded maximum number of
recycles. Last recycle due to ame failure
Check micro-amperes of ame sensor using control diagnostics or eld
installed mode. Clean or replace sensor. Measure voltage of neutral to
ground to ensure good unit ground. Alert clears after current heat call has
been completed.
E274 Soft lockout - Exceeded maximum number of
recycles. Last recycle failed due to the limit circuit
opening or limit remained open longer than 3
minutes.
Shut down system 1-hour soft lockout. Check ring rate and air ow.
Check for blockage. Clears when heat call nishes successfully.
E275 Soft lockout - Flame sensed out of sequence.
Flame signal is gone.
Shut o󰀨 gas. Check for gas valve leak. 1-hour soft lockout. Clears when
ame has been proven stable.
E276 Watchguard calibration failure. Unable to perform pressure switch calibration. Check vent system and
pressure switch wiring connections. 1-hour soft lockout. Clears when
calibration has nished successfully.
E290 Ignitor circuit fault - Failed ignitor or triggering
circuitry.
Measure resistance of hot surface igniter. Replace if open or not within
specications. 1-hour soft lockout. Clears when ame has been proven
stable.
E291 Heat airow restricted below the minimum. Check for dirty lter and airow restriction. Check blower performance.
1-hour soft lockout. Cleared when heat call nishes successfully.
E292 Indoor blower motor unable to start due to
obstructed wheel seized bearings.
Indoor blower motor unable to start (seized bearing, stuck wheel,
etc.) Replace motor or wheel if assembly does not operate or meet
performance standards. 1-hour soft lockout. Clears after circulator
successfully starts.
E294 Combustion air inducer over current. Check combustion blower bearings wiring and amps. Replace if does not
operate or does not meet performance standards. Clears after inducer
current is sensed to be in-range after the ignition following the soft lockout
or reset.
E295 Indoor blower motor temperature is too high. Indoor blower motor over temperature (motor tripped on internal
protector). Check motor bearings and amps. Replace if necessary.
Cleared after blower demand is satised.
E310 Discharge error temperature sensor failure. Only
shown if shorted or out of range.
Compare discharge sensor resistance to temperature resistance charts
in installation instructions.. Replace sensor if necessary. Cleared
in Communicating mode 30 seconds after fault recovered. In Non-
Communicating mode cleared after the current heat call is completed.
Table 5. Integrated Diagnostic Codes/Status of Equipment

508155-01Issue 2108Page 14 of 49
Code Diagnostic Codes / Status of Equipment Action Required to Clear and Recover
E311 Heat rate reduced to match indoor blower airow. Warning Only. Furnace blower in cutback mode due to restricted airow.
Reduce ring rate every 60 seconds to match available CFM. Check
lter and duct system. To clear replace lter if needed or repair/add duct.
2-stage controls will reduce ring rate to 1-stage. Clears when heat call
nished successfully.
E312 Restricted airow in cooling or continuous fan
mode is lower than CFM setting.
Warning Only. Restricted airow - Indoor blower is running at a reduced
CFM (Cutback Mode - The variable speed motor has preset speed and
torque limiters to protect the motor from damage caused by operating
outside of design parameters (0 to 0.8" W.C. total external static
pressure). Check lter and duct system. To clear, replace lter if needed
or repair/add duct. Cleared after the current service demand is satised.
E313 Indoor or outdoor unit capacity mismatch.
Communication only.
Incorrect indoor/outdoor capacity code selected. Check for proper
conguring in installation instructions. Alarm is just a warning. The system
will operate, but might not meet e󰀩ciency and capacity parameters.
Alarm will clear when commissioning is complete.
E331 Global network connection - Communications link
problem.
For Future Use.
E347 No 24 Volt output on Y1 of "integrated control"
with non-communicating outdoor unit.
Operation stopped. Y1 relay/Stage 1 failed. (Pilot relay contacts did not
close or the relay coil did not energize; no input back to IFC chip.) Critical
Alert. Cleared after reset and Y1 input sensed.
E348 No 24 Volt output on Y2 of "integrated control"
with non-communicating outdoor unit.
Y2 relay/Stage 2 failed. (Pilot relay contacts did not close or the relay coil
did not energize; no input back to IFC chip.) Critical Alert. Cleared after
reset and Y1 input sensed.
E349 No 24 Volts between R & O on "integrated
control" with non-communicating outdoor
unit (dual fuel model required for heat pump
application).
Conguration link R to O needs to be restored. Replace link or hardware.
Applicable in non-communicating mode. Critical Alert.
E401 LSOM - Compressor long run cycle or low system
pressure.
Compressor ran more that 18 hours to satisfy a single thermostat
demand. Critical Alert. Clears the error after 30 consecutive normal run
cycles or power reset. Also monitors low pressure switch trips.
E402 LSOM - Outdoor unit system pressure trip. Discharge or suction pressure out-of-limits, or compressor overloaded.
Clears the error after 4 consecutive normal compressor run cycles.
E403 LSOM - Compressor short-cycling (Running less
than 4 minutes). Outdoor unit pressure trip.
Compressor runs less than 3 minutes to satisfy a thermostat demand.
Clears the error after 4 consecutive normal run cycles or power reset.
E404 LSOM - Compressor rotor locked. Compressor
short-cycling. (Running less than 4 minutes.)
Compressor rotor locked up due to run capacitor shore, bearings
are seized, excessive liquid refrigeration, etc. Clears the error after 4
consecutive normal run cycles or power reset.
E405 LSOM - Compressor open circuit. Compressor circuit open (due to power disconnection, open fuse, etc.)
Clears the error after 1 normal compressor run cycle.
E406 LSOM - Compressor open start circuit. Required amount of current is not passing through Start current
transformer. Clears the error after current is sensed in START sensor, or
after power reset.
E407 LSOM - Compressor open run circuit. Required amount of current is not passing through Run current
transformer. Clears the error after current is sensed in RUN sensor, or 1
normal compressor run cycle, or after power reset.
E408 LSOM - Compressor contactor is welded. Compressor runs continuously. Clears the error after 1 normal
compressor run cycle or after power reset.
E409 LSOM - Compressor low voltage. Secondary voltage s below 18VAC. After 10 minutes, operation is
discontinued. Clears the code after voltage is higher than 20VAC for 2
seconds or after power reset.
Table 5. Integrated Diagnostic Codes/Status of Equipment

508155-01 Issue 2108 Page 15 of 49
NOTE: All Comfort Sync settings are set at the Comfort
Sync Wi-Fi thermostat. See Comfort Sync installation
instruction. In Comfort Sync communication system all
DIP switch and clippable link settings are ignored. For
conventional thermostats proceed with DIP switch and
clippable link settings as outlined in the following.
Heating Operation DIP Switch Settings
Switch 1 -- Thermostat Selection -- This unit may be
used with either a single-stage or two-stage thermostat.
The thermostat selection is made using a DIP switch which
must be properly positioned for the particular application.
The DIP switch is factory-positioned for use with a two-
stage thermostat. If a single-stage thermostat is to be
used, the DIP switch must be repositioned.
a. Select “OFF” for two-stage heating operation controlled
by a two-stage heating thermostat (factory setting);
b. Select “ON” for two-stage heating operation controlled
by a single-stage heating thermostat. This setting
provides a timed delay before second-stage heat is
initiated.
Switch 2 -- Second Stage Delay (Used with Single-Stage
Thermostat Only) -- This switch is used to determine the
second stage on delay when a single-stage thermostat is
being used. The switch is factory-set in the OFF position,
which provides a 7-minute delay before second-stage heat
is initiated. If the switch is toggled to the ON position, it
will provide a 12-minute delay before second-stage heat is
initiated. This switch is only activated when the thermostat
selector jumper is positioned for single-stage thermostat
use.
Switches 3 and 4 -- Blower-O󰀨 Delay -- The blower-on
delay of 30 seconds is not adjustable. The blower-o󰀨 delay
(time that the blower operates after the heating demand
has been satised) can be adjusted by moving switches 3
and 4 on the integrated control. The unit is shipped from
the factory with a blower-o󰀨 delay of 90 seconds. The
blower o󰀨 delay a󰀨ects comfort and is adjustable to satisfy
individual applications. Adjust the blower o󰀨 delay to
achieve a supply air temperature between 90° and 110°F at
the exact moment that the blower is de-energized. Longer
o󰀨 delay settings provide lower supply air temperatures;
shorter settings provide higher supply air temperatures.
Table 6 provides the blower o󰀨 timings that will result from
di󰀨erent switch settings.
Blower O󰀨 Delay
(Seconds) Switch 3 Switch 4
60 On O󰀨
90 (Factory) O󰀨 O󰀨
120 O󰀨 On
180 On On
Table 6. Blower O󰀨 Delay Switch Settings
Indoor Blower Operation DIP Switch Settings
Switches 5 and 6 -- Cooling Mode Blower Speed --
The unit is shipped from the factory with the dip switches
positioned for high speed (4) indoor blower motor operation
during the cooling mode. Table 7 provides the cooling mode
blower speeds that will result from di󰀨erent switch settings.
Switches 5 and 6 set the blower cfm for second-stage cool.
The integrated control automatically ramps down to 70% of
the second-stage cfm for rst-stage cfm. Refer to blower
tables for corresponding cfm values.
Speed Switch 5 Switch 6
Low On On
Medium Low O󰀨 On
Medium High On O󰀨
High (Factory) O󰀨 O󰀨
Table 7. Cooling Mode Blower Speeds
Switches 7 and 8 -- Cooling Blower Speed Adjustment
-- The unit is shipped from the factory with the dip switches
positioned for NORMAL (no) adjustment. The dip switches
may be positioned to adjust the blower speed by +10%
or -10% to better suit the application. Table 8 provides
blower speed adjustments that will result from di󰀨erent
switch settings. Refer to blower tables for corresponding
cfm values.
Adjustment Switch 7 Switch 8
+10% (approx.) On O󰀨
Factory Default O󰀨 O󰀨
-10% (approx.) O󰀨 On
Table 8. Cooling Blower Speed Adjustment
Switches 9 and 10 -- Cooling Mode Blower Speed
Ramping -- Blower speed ramping may be used to
enhance dehumidication performance. The switches
are factory set at option A which has the greatest e󰀨ect
on dehumidication performance. Table 9 provides the
cooling mode blower speed ramping options that will result
from di󰀨erent switch settings. The cooling mode blower
speed ramping options are detailed below.
NOTE: In heat pump mode blower operation defaults to
option C.
Ramping Option Switch 12 Switch 13
A (Factory) O󰀨 O󰀨
B O󰀨 On
COn O󰀨
D On On
Table 9. Cooling Mode Blower Speed Ramping

508155-01Issue 2108Page 16 of 49
Ramping Option A (Factory Selection)
• Motor runs at 50% for 30 seconds.
• Motor then runs at 82% for approximately 7-1/2
minutes.
• If demand has not been satised after 7-1/2 minutes,
motor runs at 100% until demand is satised.
• Once demand is met, motor runs at 50% for 30
seconds then ramps down to stop.
OFF
OFF
1/2 MIN
50% CFMCOMPRESSOR DEMAND
7 1/2 MIN
82% CFM 100% CFM 1/2 MIN
50% CFM
Ramping Option B
• Motor runs at 82% for approximately 7-1/2 minutes.
If demand has not been satised after 7-1/2 minutes,
motor runs at 100% until demand is satised.
• Once demand is met, motor ramps down to stop.
OFF
OFF 82%CFM 100% CFM
COMPRESSOR DEMAND
7 1/2 MIN
Ramping Option C
• Motor runs at 100% until demand is satised.
• Once demand is met, motor runs at 100% for 45
seconds then ramps down to stop.
OFF
OFF 100% CFM 100% CFM
45 SEC.
COMPRESSOR
DEMAND
Ramping Option D
• Motor runs at 100% until demand is satised.
• Once demand is met, motor ramps down to stop.
OFFOFF 100% CFM
COMPRESSOR
DEMAND
Switches 11, 12 and 13 -- Heating Mode Blower Speed
-- The switches are factory set to the OFF position which
provides factory default heat speed. Refer to Table 10 for
switches 11, 12 and 13 that provided the corresponding
increases or decrease to both high and low heat demand.
Heat Speed Switch 11 Switch 12 Switch 13
+24% On On On
+18% On On O󰀨
+12% On O󰀨 On
+6% On O󰀨 O󰀨
Factory Default O󰀨 O󰀨 O󰀨
-6% O󰀨 O󰀨 On
-12% O󰀨 On O󰀨
-18% O󰀨 On On
Table 10. Heating Mode Blower Speeds

508155-01 Issue 2108 Page 17 of 49
Operating Sequence System Demand System Response
System
Condition Step
Thermostat Demand Relative Humidity
Compressor Blower CFM
(COOL) Comments
Y1 O G W1 W2 Status D
NO CALL FOR DEHUMIDIFICATION
Normal Operation 1On On On Acceptable 24 VAC High 100% Compressor and indoor blower follow thermostat
demand
BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation 1On On On Acceptable 24 VAC High 100% Thermostat energizes Y1 and
de-energizes O on a call for
de-humidication
Dehumidication
Call 2 On On On Demand 0 VAC High 70%*
PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation 1On On On Acceptable 24 VAC High 100% Dehumidication mode begins
when humidity is greater than
set point
Dehumidication
Call 2 On On On Demand 0 VAC High 70%*
Dehumidication
Call ONLY 1On On On Demand 0 VAC High 70%* Thermostat will try to maintain
room humidity setpoint by
allowing the room space
to maintain a cooler room
thermostat setpoint**
• Jumpers at indoor unit with a single stage outdoor unit
• With Condensing unit - Cut W914 (R to OS) on control
• With Heat Pump - Cut W914 (R to DS) and W951 (R to O) on control
* Dehumidication blower speed is 70% of COOL speed for all units.
** In Precision mode, thermostat will maintain room temperature up to 2°F (1.2°C) cooler than room setting.
Table 11. A80US2V, Non-Communicating Thermostat with Humidity Control Feature and Single-Speed Outdoor
Unit

508155-01Issue 2108Page 18 of 49
Operating Sequence System Demand System Response
System
Condition Step
Thermostat Demand Relative Humidity
Compressor Blower CFM
(COOL) Comments
Y1 Y2 A G W1 W2 Status D
NO CALL FOR DEHUMIDIFICATION
Normal Operation
- Y1 1On On On Acceptable 24 VAC Low 70%* Compressor and indoor
blower follow thermostat
demand
Normal Operation
- Y2 2 On On On On Acceptable 24 VAC High 100%
ROOM THERMOSTAT CALLS FOR FIRST STAGE COOLING
BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation 1On On On Acceptable 24
VAC Low 70%* Thermostat energizes Y2
and de-energizes D on a
call for de-humidication
Dehumidication
Call 2 On On On On Demand 0 VAC High 70%**
PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation 1On On On Acceptable 24
VAC Low 70%* Dehumidication mode
begins when humidity is
greater than set point
Dehumidication
Call 2 On On On On Demand 0 VAC High 70%**
Dehumidication
Call ONLY 1On On On On Demand 0 VAC High 70%**
Thermostat will try to
maintain room humidity
setpoint by allowing the
room space to maintain
a cooler room thermostat
setpoint***
ROOM THERMOSTAT CALLS FOR FIRST AND SECOND STAGE COOLING
BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation 1On On On On Acceptable 24
VAC High 100% Thermostat energizes Y2
and de-energizes D on a
call for de-humidication
Dehumidication
Call 2 On On On On Demand 0 VAC High 70%**
PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation 1On On On Acceptable 24
VAC Low 70%* Dehumidication mode
begins when humidity is
greater than set point
Dehumidication
Call 2 On On On On Demand 0 VAC High 70%**
Dehumidication
Call ONLY 1On On On On Demand 0 VAC High 70%** Thermostat will try to
maintain room humidity
setpoint by allowing the
room space to maintain
a cooler room thermostat
setpoint***
• Jumpers at indoor unit with a single stage outdoor unit
• Cut factory jumper from Y1 to Y2 or cut W915 (Y1 to Y2)
• With Condensing unit - Cut W914 (R to OS) on control
• With Heat Pump - Cut W914 (R to DS) and W951 (R to O) on control
*Normal operation rst stage cooling blower speed is 70% COOL speed.
**Dehumidication blower speed is reduced to 70% of COOL.
Table 12. A80US2V, Non-Communicating Thermostat with Humidity Control Feature and Two-Speed Outdoor
Unit

508155-01 Issue 2108 Page 19 of 49
On-Board Links
NOTE: In Comfort Sync systems with a conventional
outdoor unit (non-communicating), the on-board clippable
links must be set to properly congure the system.
Carefully review all conguration information provided.
Failure to properly set DIP switches, jumpers and on-
board links can result in improper operation!
WARNING
On-Board Link W914 Dehum (R to DS)
On-board link W914, is a clippable connection between
terminals R and DS on the integrated control. W914 must
be cut when the furnace is installed with either the zone
control or a thermostat which features humidity control. If
the link is left intact the PMW signal from the control will be
blocked and also lead to control damage. Refer to Table 11
for operation sequence in applications including A80US2V,
a thermostat which features humidity control and a single-
speed outdoor unit. Table 12 gives the operation sequence
in applications with a two-speed outdoor unit.
On-Board Link W951 Heat Pump (R to O)
On-board link W951 is a clippable connection between
terminals R and O on the integrated control. W951 must
be cut when the furnace is installed in applications which
include a heat pump unit and a thermostat which features
dual fuel use. If the link is left intact, terminal “O” will remain
energized eliminating the HEAT MODE in the heat pump.
On-Board Link W915 2-Stage Compressor
(Y1 to Y2)
On-board link W915 is a clippable connection between
terminals Y1 and Y2 on the integrated control. W915 must
be cut if two-stage cooling will be used. If the link is not cut
the outdoor unit will operate in second-stage cooling only.
Indoor Blower Motor
Power Choke
(4 and 5 Ton Only) Blower Motor
(B3)
Figure 6.
During blower operation, the ECM motor emits
energy that may interfere with pacemaker operation.
Interference is reduced by both the sheet metal cabinet
and distance.
WARNING
The motor communicates with the integrated control via a
2-way serial connection. The motor receives all necessary
functional parameters from the integrated control and does
not rely on a factory program like traditional variable speed
motors. A80US2V units use a three-phase, electronically
controlled D.C. brushless motor (controller converts single
phase a.c. to three phase D.C.), with a permanent-magnet
type rotor (Figure 7). Because this motor has a permanent
magnet rotor it does not need brushes like conventional
D.C. motors.
The stator windings are split into three poles which are
electrically connected to the controller. This arrangement
allows motor windings to turn on and o󰀨 in sequence by
the controller.
Earlier ECM motors used on other Allied Air furnace
models are not interchangeable with motors used on
the A80US2V furnace line.
IMPORTANT
A solid-state controller is permanently attached to the
motor. The controller is primarily an A.C. to D.C. converter.
Converted D.C. power is used to drive the motor. The
controller contains a microprocessor which monitors
varying conditions inside the motor (such as motor
workload).

508155-01Issue 2108Page 20 of 49
STATOR
(WINDINGS)
BEARING
ROTOR
Figure 7. Blower Motor Components
The controller uses sensing devices to sense what position
the rotor is in at any given time. By sensing the position of
the rotor and then switching the motor windings on and o󰀨
in sequence, the rotor shaft turns the blower.
All A80US2V blower motors use single phase power.
An external run capacitor is not used. The motor uses
permanently lubricated ball-type bearings.
Internal Operation
The motor is controlled via serial communication between
the integrated control on the furnace and the controller
attached to the motor shell. The messages sent back
and forth between the two controls serve to communicate
rotational direction, demand, motor size, current draw,
torque, and rpm, among other variables.
Motor rpm is continually adjusted internally to maintain
constant static pressure against the blower wheel. The
controller monitors the static work load on the motor
and motor amp-draw to determine the amount of rpm
adjustment. Blower rpm may be adjusted any amount in
order to maintain a constant cfm as shown in blower tables.
The cfm remains relatively stable over a broad range of
static pressure. Since the blower constantly adjusts rpm to
maintain a specied cfm, motor rpm is not rated. Hence,
the terms “cool speed”, “heat speed” or “speed tap” in this
manual, on the unit wiring diagram and on blower B3, refer
to blower cfm regardless of motor rpm.
Initial Power Up
When line voltage is applied to B3, there will be a large
inrush of power lasting less than 1/4 second. This inrush
charges a bank of DC lter capacitors inside the controller.
If the disconnect switch is bounced when the disconnect is
closed, the disconnect contacts may become welded. Try
not to bounce the disconnect switch when applying power
to the unit.
Motor Start-Up
When B3 begins start-up, the motor gently vibrates back
and forth for a moment. This is normal. During this time
the electronic controller is determining the exact position
of the rotor. Once the motor begins turning, the controller
slowly eases the motor up to speed (this is called “soft-
start”). The motor may take as long as 10-15 seconds
to reach full speed. If the motor does not reach 200 rpm
within 13 seconds, the motor shuts down. Then the motor
will immediately attempt a restart. The shutdown feature
provides protection in case of a frozen bearing or blocked
blower wheel. The motor may attempt to start eight times.
If the motor does not start after the eighth try, the controller
locks out. Reset controller by momentarily turning o󰀨
power to unit.
The DC lter capacitors inside the controller are connected
electrically to the motor supply wires. The capacitors take
approximately 5 minutes to discharge when the disconnect
is opened. For this reason it is necessary to wait at least 5
minutes after turning o󰀨 power to the unit before attempting
to service motor.
Disconnect power from unit and wait at
least ve minutes to allow capacitors to
discharge before attempting to service
motor. Failure to wait may cause personal
injury or death.
DANGER
Power Choke (L13)
A choke coil is used on A80US2V 4 and 5 ton units
equipped with 1 hp motors. The choke is located on the
blower housing and is used to suppress transient current
spikes.
Remove Blower from Unit
1. Remove unit access panels, control box, bolts and
wiring jackplugs.
2. Slide blower out front of unit.
Troubleshooting Motor Operation
To verify motor operation see steps below and Figure 8
and Figure 9.
1. Remove J48 (5 pin power plug) from P48 on the motor.
2. With the power on at the furnace and door switch
depressed, use a test meter to verify 120V between
pins 4 and 5 on J48.
3. Reconnect J48 to P48 on the motor.
4. Remove J49 (4 pin low voltage connector) from P49
on the motor.