American Standard UHMB060ACV3VB Series Service manual

Service Facts
March 2020 UHM-DHM-SF-1V-EN
SAFETY WARNING
Only qualified personnel should install and service the equipment. The installation, starting up, and servicing of heating, ventilating,
and air-conditioning equipment can be hazardous and requires specific knowledge and training. Improperly installed, adjusted or
altered equipment by an unqualified person could result in death or serious injury. When working on the equipment, observe all pre-
cautions in the literature and on the tags, stickers, and labels that are attached to the equipment.
*UHMB060ACV3VB *DHMB060BCV3VB
*UHM *DHM
*UHMB080ACV3VB *DHMB080ACV3VB
*UHMC100ACV4VB *DHMC100ACV4VB
*UHMD120ACV5VB *DHMD120BCV5VB
Note: * First letter may be “A” or “T"
This furnace can be congured for Communicating
or 24 VAC modes.
Note: “Graphics in this document are for representation only.
Actual model may differ in appearance.”
Upow/ Horizontal Left and Downow/ Horizontal Right,
Gas-Fired, Direct/Non-Direct Vent, Variable Speed,
Modulating, Condensing, Communicating Furnaces

2 UHM-DHM-SF-1V-EN
Service Facts
PRODUCT SPECIFICATIONS ①
MODEL
TYPE
RATINGS ②
40% (low) heat Input BTUH
40% (low) heat Capacity BTUH (ICS) ③⑥
100% (high) heat Input BTUH
100% (high) heat Capacity BTUH (ICS) ③
Temp. rise (Min.-Max.) °F.
AFUE (Upflow / Horizontal)
BLOWER DRIVE
Diameter - Width (In.)
No. Used
Speeds (No.)
CFM vs. in. w.g.
Motor HP
R.P.M.
Volts / Ph / Hz
FLA ⑧
COMBUSTION FAN - Type
Drive - No. Speeds
Motor HP - RPM
Volts / Ph / Hz
FLA
FILTER — Furnished?
Type Recommended
Hi Vel. (No.-Size-Thk.)
VENT Size Min. (in.)
HEAT EXCHANGER
Type -Fired
-Unfired
Gauge (Fired)
ORIFICES — Main
Nat. Gas. Qty. — Drill Size
L.P. Gas Qty. — Drill Size ⑤
GAS VALVE
PILOT SAFETY DEVICE
Type
BURNERS — Type
Number
POWER CONN. — V / Ph / Hz ④
Ampacity (In Amps)
Max. Overcurrent Protection (Amps)
PIPE CONN. SIZE (IN.)
DIMENSIONS
Crated (In.)
WEIGHT
Shipping (Lbs.) / Net (Lbs)
*UHMB080ACV3VB ⑦
Upflow/ Horizontal
32,000
31,000
80,000
76,000
35 - 65
97.0 / 96.2
DIRECT
10 x 8
1
Variable
See Fan Performance Table
1/2
Variable
115/1/60
6.4
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
1 - 17x25 - 1 in.
2 Round
Aluminized Steel - Type I
20
4 — 45
4 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
4
115/1/60
9.2
15
1/2
H x W x D
41-3/4 x 19-1/2 x 30-1/2
168 / 156
*UHMB060ACV3VB ⑦
Upflow/ Horizontal
24,000
23,000
60,000
57,000
35 - 65
97.3 / 96.5
DIRECT
10 x 8
1
Variable
See Fan Performance Table
1/2
Variable
115/1/60
6.4
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
1 - 17x25 - 1 in.
2 Round
Aluminized Steel - Type I
20
3 — 45
3 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
3
115/1/60
9.2
15
1/2
H x W x D
41-3/4 x 19-1/2 x 30-1/2
158 / 146
*UHMC100ACV4VB ⑦
Upflow/ Horizontal
40,000
39,000
100,000
96,000
35 - 65
96.0 / 95.2
DIRECT
10 x 10
1
Variable
See Fan Performance Table
3/4
Variable
115/1/60
8.0
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
1 - 20x25 - 1 in.
2.5 Round
Aluminized Steel - Type I
20
5 — 45
5 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
5
115/1/60
11.2
15
1/2
H x W x D
41-3/4 x 23 x 30-1/2
197 / 185
*UHMD120ACV5VB ⑦
Upflow/ Horizontal
54,000
52,000
120,000
114,000
40 - 70
97.0 / 96.2
DIRECT
10 x 10
1
Variable
See Fan Performance Table
1
Variable
115/1/60
10.0
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
1 - 24x25 - 1 in.
3 Round
Aluminized Steel - Type I
20
6 — 45
6 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
6
115/1/60
13.7
15
1/2
H x W x D
41-3/4 x 26-1/2 x 30-1/2
206 / 193
①Central Furnace heating designs are certified to ANSI Z21.47 / CSA 2.3.
②For U.S. applications, above input ratings (BTUH) are up to 2,000 feet, derate 4% per 1,000 feet for elevations above 2,000 feet above sea level.
For Canadian applications, above input ratings (BTUH) are up to 4,500 feet, derate 4% per 1,000 feet for elevations above 4,500 feet above sea level.
③Based on U.S. government standard tests.
④The above wiring specifications are in accordance with National Electrical Code; however, installations must comply with local codes.
⑤Furnace ships in natural gas configuration. The LP conversion kit used with the modulating furnace is BAYLPSS220B or BAYLPKT220B.
⑥45% (low) heat for *UHMD120ACV5VB.
⑦EnergyStar
⑧Check motor nameplate for actual FLA
DISCONNECT POWER BEFORE SERVICING
WARNING
IMPORTANT - This document contains a wiring diagram and service information.This is customer property
and is to remain with this unit. Please return to service information pack upon completion of work.

UHM-DHM-SF-1V-EN 3
Service Facts
PRODUCT SPECIFICATIONS ①
MODEL
TYPE
RATINGS ②
40% (low) heat Input BTUH
40% (low) heat Capacity BTUH (ICS) ③
100% (high) heat Input BTUH
100% (high) heat Capacity BTUH (ICS) ③
Temp. rise (Min.-Max.) °F.
AFUE
BLOWER DRIVE
Diameter - Width (In.)
No. Used
Speeds (No.)
CFM vs. in. w.g.
Motor HP
R.P.M.
Volts / Ph / Hz
FLA ⑦
COMBUSTION FAN - Type
Drive - No. Speeds
Motor HP - RPM
Volts / Ph / Hz
FLA
FILTER — Furnished?
Type Recommended
Hi Vel. (No.-Size-Thk.)
VENT Size Min. (in.)
HEAT EXCHANGER
Type -Fired
-Unfired
Gauge (Fired)
ORIFICES — Main
Nat. Gas. Qty. — Drill Size
L.P. Gas Qty. — Drill Size ⑤
GAS VALVE
PILOT SAFETY DEVICE
Type
BURNERS — Type
Number
POWER CONN. — V / Ph / Hz ④
Ampacity (In Amps)
Max. Overcurrent Protection (Amps)
PIPE CONN. SIZE (IN.)
DIMENSIONS
Crated (In.)
WEIGHT
Shipping (Lbs.) / Net (Lbs)
*DHMB080ACV3VB ⑥
Downflow / Horizontal
32,000
32,000
80,000
76,000
35 - 65
96.0
DIRECT
10 x 8
1
Variable
See Fan Performance Table
1/2
Variable
115/1/60
6.4
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
2 - 14x20 - 1 in.
2 Round
Aluminized Steel - Type I
20
4 — 45
4 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
4
115/1/60
9.2
15
1/2
H x W x D
41-3/4 x 19-1/2 x 30-1/2
168 / 158
*DHMD120BCV5VB ⑥
Downflow / Horizontal
48,000
47,000
120,000
114,000
40 - 70
95.0
DIRECT
10 x 10
1
Variable
See Fan Performance Table
1
Variable
115/1/60
10.0
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
2 - 16x20 - 1 in.
3 Round
Aluminized Steel - Type I
20
6 — 45
6 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
6
115/1/60
13.7
15
1/2
H x W x D
41-3/4 x 26-1/2 x 30-1/2
206 / 196
*DHMC100ACV4VB ⑥
Downflow / Horizontal
40,000
39,000
100,000
96,000
35 - 65
96.0
DIRECT
10 x 10
1
Variable
See Fan Performance Table
3/4
Variable
115/1/60
8.0
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
2 - 16x20 - 1 in.
2.5 Round
Aluminized Steel - Type I
20
5 — 45
5 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
5
115/1/60
11.2
15
1/2
H x W x D
41-3/4 x 23 x 30-1/2
185 / 175
*DHMB060BCV3VB ⑥
Downflow / Horizontal
24,000
23,000
60,000
57,000
30 - 60
95.0
DIRECT
10 x 8
1
Variable
See Fan Performance Table
1/2
Variable
115/1/60
6.4
Centrifugal
Direct - Variable
1/50 - 5000
115/3/60
1.0
Ye s
High Velocity
2 - 14x20 - 1 in.
2 Round
Aluminized Steel - Type I
20
3 — 45
3 — 56
Modulating
Hot Surface Igniter
Multiport Inshot
3
115/1/60
9.2
15
1/2
H x W x D
41-3/4 x 19-1/2 x 30-1/2
160/ 146
①Central Furnace heating designs are certified to ANSI Z21.47 / CSA 2.3.
②For U.S. applications, above input ratings (BTUH) are up to 2,000 feet, derate 4% per 1,000 feet for elevations above 2,000 feet above sea level.
For Canadian applications, above input ratings (BTUH) are up to 4,500 feet, derate 4% per 1,000 feet for elevations above 4,500 feet above sea level.
③Based on U.S. government standard tests.
④The above wiring specifications are in accordance with National Electrical Code; however, installations must comply with local codes.
⑤Furnace ships in natural gas configuration. The LP conversions kit used with the modulating furnace is BAYLPSS220B or BAYLPKT220B.
⑥EnergyStar
⑦Check motor nameplate for actual FLA
NOTE:
This furnace can be configured for Communicating or
24 VAC modes. Using fully Communicating or 24 VAC
modes, the furnace can support single or multi stage
heat pump, AC, or heating only applications. Com-
bined with a communicating Comfort Control only,
the furnace will support a single stage 24 VAC cooling
outdoor unit only.
ENERGY EFFICIENT OPERATION
Furnace is certified to leak 2% or less of nominal air
conditioning CFM delivered when pressurized to .5” water
column with all inlets, outlets, and drains sealed.
NOTE:
CONTINUOUS fan mode during COOLING operation
may not be appropriate in humid climates. If the in-
door air exceeds 60% relative humidity or simply feels
uncomfortably humid, it is recommended that the fan
only be used in the AUTO mode.
A communicating comfort control will disable a con-
tinuous fan call if the relative humidity exceeds the set
point. See the Troubleshooting Information section of
the Communicating Comfort Control Installer’s Guide
for details.

4 UHM-DHM-SF-1V-EN
Service Facts
SAFETY SECTION
WARNING
!
FIRE OR EXPLOSION HAZARD
Failure to follow the safety warnings exactly could re-
sult in serious injury, death or property damage.
Never test for gas leaks with an open flame. Use a
commercially available soap solution made specifically
for the detection of leaks to check all connections. A
fire or explosion may result causing property damage,
personal injury, or loss of life.
WARNING
!
FIRE OR EXPLOSION HAZARD
Failure to follow the safety warnings exactly could re-
sult in serious injury, death or property damage.
Improper servicing could result in dangerous opera-
tion, serious injury, death, or property damage.
WARNING
!
BODILY INJURY CAN RESULT FROM HIGH VOLTAGE
ELECTRICAL COMPONENTS, FAST MOVING FANS,
AND COMBUSTIBLE GAS. FOR PROTECTION FROM
THESE INHERENT HAZARDS DURING INSTALLATION
AND SERVICING, THE ELECTRICAL SUPPLY MUST BE
DISCONNECTED AND THE MAIN GAS VALVE MUST
BE TURNED OFF. IF OPERATING CHECKS MUST BE
PERFORMED WITH THE UNIT OPERATING, IT IS THE
TECHNICIAN’S RESPONSIBILITY TO RECOGNIZE
THESE HAZARDS AND PROCEED SAFELY.
WARNING
!
Should overheating occur, or the gas supply fail to
shut off, shut off the Gas Valve to the unit before shut-
ting off the electrical supply.
Failure to follow this warning could result in property
damage, personal injury, or death.
CAUTION
!
The integrated furnace control is polarity sensitive. The
hot leg of the 115 VAC power must be connected to the
BLACK field lead
NOTE:
CONTINUOUS fan mode during COOLING operation
may not be appropriate in humid climates. If the in-
door air exceeds 60% relative humidity or simply feels
uncomfortably humid, it is recommended that the fan
only be used in the AUTO mode.
A communicating comfort control will disable a con-
tinuous fan call if the relative humidity exceeds the set
point. See the Troubleshooting Information section of
the Communicating Comfort Control Installer’s Guide
for details.
WARNING
!
The cabinet must have an uninterrupted or unbroken
ground according to National Electrical Code, ANSI/
NFPA 70 - “latest edition” and Canadian Electrical
Code, CSA C22.1 or local codes to minimize personal
injury if an electrical fault should occur.
Failure to follow this warning could result in an electri-
cal shock, fire, injury, or death.
WARNING
!
CARBON MONOXIDE POISONING HAZARD
Failure to follow the installation instructions for the
venting system being placed into operation could re-
sult in carbon monoxide poisoning or death.
CARBON MONOXIDE POISONING HAZARD
Failure to follow the steps outlined below for each
appliance connected to the venting system being
placed into operation could result in carbon monoxide
poisoning or death.
The following steps shall be followed for each appliance
connected to the venting system being placed into
operation, while all other appliances connected to the
venting system are not in operation:
1. Seal any unused openings in the venting system.
2. Inspect the venting system for proper size and
horizontal pitch, as required in the National Fuel Gas
Code, ANSI Z223.1/NFPA 54 or the CAN/CGA B149
Installation Codes and these instructions. Determine
that there is no blockage or restriction, leakage,
corrosion and other deficiencies which could cause an
unsafe condition.
3. As far as practical, close all building doors and
windows and all doors between the space in which the
appliance(s) connected to the venting system are
located and other deficiencies which could cause an
unsafe condition.
4. Close fireplace dampers.
5. Turn on clothes dryers and any appliance not
connected to the venting system. Turn on any exhaust
fans, such as range hoods and bathroom exhausts, so
they are operating at maximum speed. Do not operate
a summer exhaust fan.
6. Follow the lighting instructions. Place the appliance
being inspected into operation. Adjust the thermostat
so appliance is operating continuously.
7. If improper venting is observed during any of the above
tests, the venting system must be corrected in
accordance with the National Fuel Gas Code,
ANSI Z221.1/NFPA 54 and/or CAN/CGA B149
Installation Codes.
8. After it has been determined that each appliance
connected to the venting system properly vents where
tested as outlined above, return doors, windows,
exhaust fans, fireplace dampers and any other gas-fired
burning appliance to their previous conditions of use.
WARNING
!

UHM-DHM-SF-1V-EN 5
Service Facts
Heat Exchanger (Cold Header)
Burner Box
H-Fitting
Pressure
Switch
PS-1
Tee
Tee
Tee
Pressure Switch
PS-3
Pressure
Switch
PS-2
Negative
Control
Pressure
Post
Positive Control
Pressure Post
Modulating
Gas Valve
Orifice in H fitting must
be pointing away from PS1
FURNACE COMPONENTS
To Pressure
Switch PS-1
! Important !
Brass orifices located in these two legs.
H-Fitting must be installed in this orientation.
VACUUM HOSE ROUTING
WARNING
!
FIRE - EXPLOSION HAZARD
DO NOT RUN FLEXIBLE GAS LINE THROUGH THE
FURNACE CABINET WALL OR WITHIN THE FUR-
NACE CABINET. FAILURE TO FOLLOW THIS WARNING
COULD RESULT IN PROPERTY DAMAGE, SERIOUS
PERSONAL INJURY, OR DEATH.
1
2
3

6 UHM-DHM-SF-1V-EN
Service Facts
USER INTERFACE DISPLAY
USER INTERFACE
ENTER
Push left & right
to scroll through
menu options
Push up & down
to scroll through
setup menu
Push ENTER
to make selection
Viewing Window
User Interface pictured above adjusts variable speed airflow options and other unit settings
Service procedure to access the User In-
terface for the Modulating Furnace
This procedure must only be performed by trained ser-
vice personnel.
WARNING
!
ELECTRICAL SHOCK HAZARD
DO NOT BYPASS THE DOOR SWITCH BY ANY PER-
MANENT MEANS.
FAILURE TO FOLLOW WARNING COULD RESULT IN
SERIOUS PERSONAL INJURY OR DEATH.
WARNING
!
ELECTRICAL SHOCK HAZARD
DO NOT TOUCH ANY COMPONENTS OTHER THAN THE
DISPLAY ASSEMBLY AND THE DOOR SWITCH DURING
THIS PROCEDURE.
FAILURE TO FOLLOW WARNING COULD RESULT IN
SERIOUS PERSONAL INJURY OR DEATH.
1. Remove Blower Door panel by turning the two
door latches ¼ turn.
2. Lower door panel and remove from service access
area.
3. Using one hand, depress the door switch (there
must be power to the control system for the Dis-
play Assembly to function) and keep the door
switch depressed during programming.
4. Using the other hand move through the Display
Assembly menu using the arrow buttons.
5. The User Interface menu on pages 7 and 8 is a guide
to the menu options.
6. When programming is complete release door
switch and replace the Blower Door.
4

UHM-DHM-SF-1V-EN 7
Service Facts
USER INTERFACE MENU
Power Up
== WAIT ==
A/TCONT900 Variable Speed
Standy Screen System Status Setup Options [ ] = Current Setting
MODEL NUMBER CMFRT CNT MODE
SERIAL NUMBER COMM [COMM] 24VAC
* Unit specific
COOLING CFM 2COOLING CFM A/TUHMB060 3T [3T] 1.5T 2T 2.5T
* A/TUHMB080 3T [3T] 3.5T 2T 2.5T
A/TUHMC100 4T [4T] 2.5T 3T 3.5T
CFM PER TON CFM PER TON A/TUHMD120 5T [5T] 3.5T 4T
400 [ 400 ] 430 450 290 310 330 350 370 A/TDHMB060 3T [3T] 1.5T 2T 2.5T
A/TDHMB080 3T [3T] 3.5T 2T 2.5T
HEAT CFM HEAT CFM A/TDHMC100 4T [4T] 2.5T 3T 3.5T
** A/TDHMD120 5T [5T] 3.5T 4T
HT OFF DELAY HEAT OFF DLY ** Unit specific
100s [100s] 140s 180s 60s A/TUHMB060 960 [960] 1080 830 900
A/TUHMB080 1400 [1400] 1610 1120 1260
FACTORY DEFLTS FACTORY DEFLTS A/TUHMC100 1620 [1620] 1790 1460 1540
NO [NO] YES A/TUHMD120 1890 [1890] 2000 1700 1790
A/TDHMB060 1040 [1040] 1160 900 950
EXIT EXIT A/TDHMB080 1400 [1400] 1610 1300 1350
NO [NO] YES A/TDHMC100 1650 [1650] 1700 1500 1600
A/TDHMD120 1850 [1850] 2040 1660 1760
Information Menu Information Options
MODEL NUMBER MODEL
A/TUHM####
SERIAL NUMBER SERIAL
#####
SW REV NUMBER SW REV NUMBER
#####
SYSTEM STATUS SYSTEM STATUS
OFF
REQUESTED CFM REQUESTED CFM
0 CFM
LAST 4 FAULTS LAST 4 FAULTS
NO ALERTS
INDOOR ALERTS INDOOR ALERTS
NO ALERTS
UNIT TEST UNIT TEST UNIT TEST UNIT TEST
SIMPLE GAS VAL SETUP
TEMP SENSOR TEMP SENSOR
SNSR1 [SNSR1] SNSR2 DLT2-1
UNIT TEST SIMPLE GAS VAL SETUP
MOTOR RPM MOTOR RPM NO [NO] YES MIN [MIN] MAX
0 RPM
INDUCER RPM INDUCER RPM
0 RPM ARE YOU SURE ARE YOU SURE
NO [NO] YES NO [NO] YES
RESET LST FAULT RESET LST FAULT
NO [NO] YES
PART LIST PART LIST
CNT*****
PM SERIAL NUM PM SERIAL NUM
#####
CNTNGNCY MODE CNTNGNCY MODE OR CNTNGNCY MODE 1
NOT AVAILABLE (with data line connected and active) NO [YES] YES (no data line connected)
EXIT EXIT
NO [NO] YES CNTNGNCY MODE <STAGE> CNTNGNCY MODE <STAGE>
STAGE [OFF] OFF 1 2
DUTY CYCLE [10] 10 20 30 40 50
START [NO] NO YES
NOTES: EXIT [NO] NO YES
1This menu will only display at comfort control mode when A/TCONT900 is NOT connected
ARE YOU SURE [NO] NO YES
ENTER
2Shown only when Communicating Outdoor Unit is not detected
ENTER
ENTER
ENTER

8 UHM-DHM-SF-1V-EN
Service Facts
24V Variable Speed
System Status Setup Options [ ] = Current Setting
CMFRT CNT MODE
COMM [24VAC] 24VAC
* Unit specific
A/TUHMB060 3T [3T] 1.5T 2T 2.5T
COOLING CFM 2COOLING CFM A/TUHMB080 3T [3T] 3.5T 2T 2.5T
* A/TUHMC100 4T [4T] 2.5T 3T 3.5T
A/TUHMD120 5T [5T] 3.5T 4T
CFM PER TON CFM PER TON A/TDHMB060 3T [3T] 1.5T 2T 2.5T
400 [ 400 ] 430 450 290 310 330 350 370 A/TDHMB080 3T [3T] 3.5T 2T 2.5T
A/TDHMC100 4T [4T] 2.5T 3T 3.5T
CLG STAGES CLG STAGES A/TDHMD120 5T [5T] 3.5T 4T
1 STG [1 STG] 2 STGS
** Unit specific
CLG 1ST STG CFM 3CLG 1ST STG CFM 2A/TUHMB060 960 [960] 1080 830 900
50% [50%] 55% 65% 80% A/TUHMB080 1400 [1400] 1610 1120 1260
A/TUHMC100 1620 [1620] 1790 1460 1540
CONT FAN CFM A/TUHMD120 1890 [1890] 2000 1700 1790
CONT FAN CFM
50% [50%] 25% A/TDHMB060 1040 [1040] 1160 900 950
A/TDHMB080 1400 [1400] 1610 1300 1350
FAN PRERUN DLY FAN PRERUN DLY A/TDHMC100 1650 [1650] 1700 1500 1600
NONE [NONE] 1m@50% A/TDHMD120 1850 [1850] 2040 1660 1760
FAN SHRTRUN DLY FAN SHRTRUN DLY
NONE [NONE] 4m@80% 7.5m@80%
FAN OFF DLY FAN OFF DLY
1.5m@100% [1.5m@100%] NONE 1m@50% 2m@50% 3m@50%
HEAT CFM HEAT CFM
**
HT OFF DELAY HT OFF DELAY
100s [100s] 140 180 60
W1 W2 STG DLY W1 W2 STG DLY
00m [00m] 5m 10m 15m
FACTORY DEFLTS FACTORY DEFLTS
NO [NO] YES
EXIT EXIT
NO [NO] YES
NOTES:
3
This menu will only display when 2 STGS is chosen in previous menu.
2Shown only when Communicating Outdoor Unit is not detected

UHM-DHM-SF-1V-EN 9
Service Facts
NOTE: Y1 is output to non-communicating outdoor unit
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Communicating
Comfort Control
SEQUENCE OF OPERATION
SEQUENCE OF OPERATION – COMMUNICATING
MODE
1. This furnace is fully modulating between 40% and
100% of capacity in 1% increments. The furnace
always lights at approximately 65% and will modulate
up or down; depending on the communicating com-
fort control demand. Requested capacity can be seen
in the “STATUS” section of the User Interface menu.
Note:
Pressure Switch 1 closes at approximately 40%
of capacity.
Pressure Switch 2 closes at approximately 65%
of capacity.
Pressure Switch 3 closes at approximately 95%
of capacity.
2. The communicating comfort control signals the fur-
nace IFC for heat.
3. The IFC then checks all safeties, thermostats, and
pressure switches PS1, PS2, and PS3.
4. The IFC signals the variable speed inducer drive to
start the vent motor at the speed needed to close
pressure switches PS1 and PS2.
5. PS1 and PS2 close.
6. The IFC receives a 24 VAC signal from PS1 and PS2
when they close. This verifies the vent motor is mov-
ing the correct amount of combustion air through the
furnace and the vent system.
7. IFC starts the hot surface ignitor learning routine
warm-up time cycle.
8. IFC turns on the gas valve. Trial time for ignition is 5
seconds.
Note:
The furnace lights at approximately 65% of capacity.
9. The IFC verifies ignition by the flame current sensing
method. If a flame is not detected, the IFC will cycle
the furnace three times to try and verify a flame. If no
flame is detected, the IFC will lockout for one hour.
The IFC will send an alert code to the communicat-
ing comfort control and User Interface. The Red alert
LED two times repeatedly.
10. If a flame is detected, the IFC will start the heat ex-
changer warm-up time delay for the indoor blower.
11. “IGNITION” will now be displayed in the “STATUS”
section of the User Interface menu.
12. After 45 seconds, the IFC signals the indoor blower
motor to run at the programmed ignition sequence
speed.
13. Depending on the communicating comfort control
demand, the IFC will then signal the variable speed
inducer motor drive board and the indoor blower mo-
tor to ramp up or down.
14. With a heat demand less than 65% from the commu-
nicating comfort control, the IFC signals the variable
speed inducer motor drive board to ramp down to
that corresponding demand speed. The reduction
5

10 UHM-DHM-SF-1V-EN
Service Facts
of the vent motor speed in steps allows the gas flow
through the gas valve to also be reduced in steps,
decreasing the chance of burner flame out. The mini-
mum capacity change is 1%.
15. The minimum capacity of all furnaces is 40%, with
the exception of the *UHMD120. The minimum ca-
pacity for this furnace is 45%.
16. The communicating comfort control will continue
to call for the requested capacity demand until the
indoor temperature is back at the set point OR,
17. If the communicating comfort control does not detect
that the indoor temperature is moving back towards
its set point or the indoor temperature is still moving
away from the set point, it will signal the IFC to go to
a higher capacity of heat.
18. The IFC then signals the variable speed inducer drive
to ramp up the vent motor in steps. As the vent motor
speed increases the amount of gas coming through
the gas valve will increase. The IFC will also increase
the indoor blower motor speed.
19. The communicating comfort control will continue to
monitor the indoor temperature and send signals to
the IFC to modulate the heating capacity or turn off to
maintain the homeowner's set point.
20. Once the communicating comfort control senses
that the heating requirements have been satisfied,
the gas valve will be de-energized and gas flow
will cease. The variable speed vent motor will de-
energize approximately after a 5 second post purge.
All pressure switches will open and the indoor blower
motor will then run the heat off delay that is selected
in the User Interface menu.
Indoor Blower motor operation thermostat fan switch
“ON” (Communicating Mode)
The communicating comfort control signals a continu-
ous fan call. The factory setting is 50% of the cooling cfm
selected but can be adjusted from 25% - 100% through
the Installer Setup menu on the communicating comfort
control. If the outdoor unit is a 2 stage system, the fac-
tory setting is 50% of the 2nd stage cooling cfm. If the
outdoor unit is a 24 volt single stage cooling system, the
factory setting is 50% of the cooling cfm.
NOTE: If the actual relative humidity (RH) is at or below
the set-point, the fan will run until the continuous fan call
is removed or the actual RH exceeds the set-point. If the
actual RH is above the set-point, the fan will not turn on.
See the communicating comfort control Installer's Guide
for additional information.
SEQUENCE OF OPERATION – 24VAC Mode
1. This furnace modulates between 40% and 100% of
capacity, in 3% increments, every 1 minute. The
furnace always lights at approximately 65% and will
modulate up or down; depending on the 24VAC ther-
mostat signal. Requested capacity can be seen in the
“STATUS” section of the User Interface menu.
Note:
Pressure Switch 1 closes at approximately 40% of
capacity.
Pressure Switch 2 closes at approximately 65% of
capacity.
Pressure Switch 3 closes at approximately 95% of
capacity.
Thermostat call for W1 (2 stage heating thermostat)
2. R and W1 contacts close signaling the control board
(IFC) to run its self- check routine. After the control
has verified that all safeties are closed and PS1,
PS2, and PS3 pressure switch contacts are open, the
IFC signals the variable speed inducer drive to start
the vent motor at the speed needed to close pressure
switches PS1 and PS2.
Note:
The furnace lights at approximately 65% of capacity.
3. PS1 and PS2 close.
4. The IFC receives a 24 VAC signal from PS1 and PS2
when they close. This verifies the vent motor is mov-
ing the correct amount of combustion air through the
furnace and the vent system.
5. IFC starts the hot surface ignitor learning routine
warm-up time cycle.
6. IFC turns on the gas valve. Trial time for ignition is 5
seconds.
7. The IFC verifies ignition by the flame current sensing
method. If a flame is not detected, the IFC will cycle
the furnace three times to try and verify a flame. If no
flame is detected, the IFC will lockout for one hour.
The IFC will send an alert code to the communicating
comfort control and User Interface as well as flash its
Red alert LED two times repeatedly.
8. If a flame is detected, the IFC will start the heat ex-
changer warm-up time delay for the indoor blower.
9. “IGNITION” will now be displayed in the “STATUS” sec-
tion of the User Interface menu.
10. After 45 seconds, the IFC signals the indoor blower
motor to run at the programmed ignition sequence
speed.
11. The IFC then signals the variable speed inducer mo-
tor drive board to ramp down to the corresponding
speed to keep PS1 closed. The reduction of the vent
motor speed in steps allows the gas flow through the
gas valve to also be reduced in steps, decreasing the
chance of burner flame out. The W1 heating capacity
is 40%. The IFC will also decrease the indoor blower
motor speed.
Thermostat call for W2 after W1
12. R and W2 thermostat contacts close signaling a call
for W2 heat. The IFC then signals the variable speed
inducer drive to ramp up the vent motor allowing flow
through the gas valve to also be increased in 3%
steps.

UHM-DHM-SF-1V-EN 11
Service Facts
13. If the call for W2 remains, this 3% increase will be
repeated every 1 minute until the capacity requested
is 100%. The IFC will also increase the indoor blower
motor speed in appropriate steps.
W2 satisfied, W1 still called for
14. R and W2 thermostat contacts open signaling that
W2 heating requirements have been satisfied. The
IFC will signal the variable speed vent motor to slow
down to its learned W1 speed. The gas valve will
reduce the gas flow to 40% capacity and the indoor
blower motor speed will be reduced.
W1 satisfied
15. R and W1 thermostat contacts open signaling that
W1 heating requirements have been satisfied. The
gas valve will be de-energized and gas flow will
cease. The variable speed vent motor will de-ener-
gize approximately after a 5 second post purge.
The indoor blower motor will be de-energized af-
ter the fan off delay period has ended. (The indoor
blower heat fan off delay is field selectable and can
be adjusted using the User Interface menu. It is fac-
tory set at 100 seconds but can be set to 60, 140, or
180 seconds)
Thermostat call for heat (1 stage heating thermostat)
16. W1 and W2 must be jumpered at the IFC. R and
W1 contacts close signaling the control board (IFC)
to run its self- check routine. After the control has
verified that all safeties are closed and PS1, PS2,
and PS3 pressure switch contacts are open, the IFC
signals the variable speed inducer drive to start the
vent motor at the speed needed to close pressure
switches PS1 and PS2.
Note:
The furnace lights at approximately 65% of capacity.
17. PS1 and PS2 close.
18. The IFC receives a 24 VAC signal from PS1 and PS2
when they close. This verifies the vent motor is mov-
ing the correct amount of combustion air through the
furnace and the vent system.
19. IFC starts the hot surface ignitor learning routine
warm-up time cycle.
20. IFC turns on the gas valve. Trial time for ignition is 5
seconds.
21. The IFC verifies ignition by the flame current sensing
method. If a flame is not detected, the IFC will cycle
the furnace three times to try and verify a flame. If no
flame is detected, the IFC will lockout for one hour.
The IFC will send an alert code to the communicating
comfort control and User Interface as well as flash its
Red alert LED two times repeatedly.
22. If a flame is detected, the IFC will start the heat ex-
changer warm-up time delay for the indoor blower.
23. “IGNITION” will now be displayed in the “STATUS”
section of the User Interface menu.
24. After 45 seconds, the IFC signals the indoor blower
motor to run at the programmed ignition sequence
speed.
25. Every 1 minute, the IFC will signal the vent motor
to ramp up. The increase of the vent motor speed
allows the gas flow through the gas valve to also
be increased in 3% steps. This 3% increase will be
repeated every 1 minute until the capacity requested
is 100%. Pressure switch 3 closes at approximately
95% of capacity.
26. The IFC will also increase the indoor blower motor
speed in appropriate steps. (The inter-stage delay is
field selectable and can be adjusted through the User
interface menu.
It is factory set at 0 minutes but can be adjusted to 5,
10, or 15 minutes.) This option can help optimize the
furnace to try to satisfy the heating requirement dur-
ing low heating load conditions.
Indoor Blower motor operation thermostat fan switch
“CONTINUOUS” (24V Mode)
R and G comfort control contacts close signaling a con-
tinuous fan call. The continuous fan cfm is field selectable
and can be adjusted through the User Interface menu.
The factory setting is 50% of the cooling cfm selected but
can be set at 25%. If the system has a 2 stage outdoor
unit, the setting is 50% of the 2nd stage cooling cfm.

12 UHM-DHM-SF-1V-EN
Service Facts
B) GAS VALVE SETUP (MANIFOLD PRESSURE
ADJUSTMENT)
NOTE: To obtain an accurate manifold pressure
measurement ,the manifold pressure must be refer-
enced to the burner box, since the burner box pres-
sure tap equalizes the gas valve pressure regulator.
To do so, install a tee and section of tube (field sup-
plied) in the tubing between the tee coming from the
burner box tube and the gas valve manifold pressure
measurement fitting. This tube and tee is in addition
to the tube attached to the gas valve pressure tap on
the outlet side of the gas valve. See Figure 7.
NOTE: In order to properly set the manifold gas
pressure, the incoming line gas pressure should be
tested with the unit off and again with the unit oper-
ating at the high heat setting to ensure adequate fuel
supply to the furnace. The incoming gas pressure
should be 5" W.C. minimum and 13.8" W.C. maximum
for natural gas.
1) Before Setting Manifold Gas Pressure
Setting the manifold gas pressures is critical for the cor-
rect operation of this furnace.
Before entering the Gas Valve Setup mode:
a. Turn comfort control system switch to the OFF posi-
tion and fan switch to the AUTO position.
b. Prime the furnace condensate trap.
Any call for heat or fan by the comfort control will abort
or cancel the Gas Valve Setup mode. The unit will
stay in Gas Valve Setup mode for a maximum of 20
minutes.
c. Connect dual port manometer & field tubing per Fig-
ure 6.
Note: MIN = 40% (low) heat, MAX = 100% (high) heat
Setting Manifold Gas Pressure
2) Setting “MIN” manifold gas pressure
To enter the Gas Valve Setup mode:
a. Scroll down on the user interface to Unit Test.
b. Scroll to the right and select “Gas Val Setup”.
c. Push the Enter button.
d. Select “MIN” and push the Enter button.
e. When asked “Are You Sure”, select Yes, and push the
Enter button.
f. The furnace will now begin the ignition sequence.
g. If pressure switch 1 & 2 learning routines have not
been performed; after successful ignition, the inducer
will go through this operation. (see Inducer Learning
Routine section).
UNIT TEST MODE
A) SIMPLE
Note:
Stage 1 = 40% (low) heat, Stage 2 = 100% (high) heat
A qualified technician can cycle the Variable Speed
Indoor Blower and the Modulating Gas Furnace
through its operation at the User Interface.
•The unit test cycle is entered at the user
interface.
•The test cycle can only be entered when the
comfort control has no demand and the furnace
IFC is not reporting a fault. Turn the comfort
control to the Off position and turn the fan
control to Auto. This will ensure the unit
test cycle will not be interrupted.
•Scroll down using the button at the user
interface until the display reads:
•UNIT TEST. Press the Enter button.
•UNIT TEST and NO (NO) will now be
displayed. Use the or arrow button to
change the NO to a YES and then press ENTER.
•ARE YOU SURE and NO (NO) will now be
displayed. Use the or arrow button to
change the NO to a YES and then press ENTER.
• UNIT TEST and Y1 ON FAN ON will now be dis-
played. The variable speed indoor blower will
then be turned on by the IFC for 10 seconds and
then off.
•Furnace will then transition to the ignition sequence.
STAGE OFF will now be displayed. After a 45 sec-
ond heat fan on delay, Stage 1 will be displayed and
40% (low) heat inducer speed will be energized for
10 seconds.
•Stage 2 will be displayed and 100% (high) heat in-
ducer speed will be energized for 10 seconds.
•The control transitions to off.
•The Model and Serial Number will be displayed.
•The variable speed indoor blower will now
operate for the heat exchanger cool down cycle
and then shut off at the end of the cycle.
•The comfort control can now be returned to the
homeowner’s desired settings.

UHM-DHM-SF-1V-EN 13
Service Facts
CORRECT METHOD OF CHECKING DIRECT VENT MANIFOLD PRESSURE
WITH BURNER BOX REFERENCED
Manifold
Pressure
Measurement
Fitting
Field Supplied
Connects to
Burner Box
Pressure Hose
A Field Supplied barb fitting must be used
on the gas valve to attach the hose
Gas Valve
On/ Off
Toggle
Switch
High Heat
Manifold
Pressure
(Adjustment
under cover)
Inlet Pressure
Measurement Fitting
7
Negative Control
Pressure Post
Positive Control
Pressure Post
Low Heat Manifold
Pressure
(Adjustment under
cover)
Manifold
Pressure
Measurement
Fitting
Flow
TABLE 1
Furnace Input
rate (KBTU/hr)
FINAL LP MANIFOLD PRESSURE SETTINGS
(inches w.c.)
40% 65% 100%
60 2.1 ± 0.5 Not Adjustable 10.0 ± 0.5
80 2.1 ± 0.5 Not Adjustable 10.0 ± 0.5
100 2.1 ± 0.5 Not Adjustable 10.0 ± 0.5
Downflow 120 2.1 ± 0.5 Not Adjustable 10.0 ± 0.5
Upflow 120 2.9 ± 0.5 Not Adjustable 10.0 ± 0.5
For upflow 120KBTU/hr model, 1st stage is 45%
Manifold pressures apply for Propane applications ONLY
Furnace Input
rate (KBTU/hr)
FINAL NG MANIFOLD PRESSURE SETTINGS
(inches w.c.)
40% 65% 100%
60 0.7 + 0.2 / - 0.0 Not Adjustable 3.5 ± 0.2
80 0.7 + 0.2 / - 0.0 Not Adjustable 3.5 ± 0.2
100 0.7 + 0.2 / - 0.0 Not Adjustable 3.5 ± 0.2
Downflow 120 0.7 + 0.2 / - 0.0 Not Adjustable 3.5 ± 0.2
Upflow 120 0.9 + 0.2 / - 0.0 Not Adjustable 3.5 ± 0.2
For upflow 120KBTU/hr model, 1st stage is 45%
Manifold pressures apply for Natural Gas applications ONLY
WARNING
!
EXPLOSION HAZARD
REPLACE AND/OR
TIGHTEN ALL PLUGS
REMOVED OR LOOS-
ENED WHEN ADJUSTING
GAS PRESSURE. LEAK
CHECK THE FITTINGS
BEFORE PLACING INTO
REGULAR SERVICE.
FAILURE TO FOLLOW
THIS WARNING COULD
RESULT IN SERIOUS
PERSONAL INJURY,
PROPERTY DAMAGE,
OR DEATH
Slope
Gauge
6

14 UHM-DHM-SF-1V-EN
Service Facts
h. Allow 5 minutes to pass before attempting to adjust
the 40% manifold pressure. This will insure that the
learning routine is complete and that the heat rise is
stable.
j. Read the 40% manifold pressure.
k. If needed, remove the low heat manifold adjustment
cover and adjust to obtain the correct manifold pres-
sure. See Figure 7.
40% (LOW) HEAT ADJUSTMENT: TURN CLOCKWISE
TO DECREASE MANIFOLD PRESSURE OR COUN-
TERCLOCKWISE TO INCREASE MANIFOLD PRES-
SURE.
l. Use Manifold Pressure Settings Table 1 for the cor-
rect manifold pressure setting in Inches of Water
Column.
m. Once the 40% manifold pressure has been adjusted;
push the Enter button on the user interface. This will
stop the gas valve setup mode and take you back to
the home screen.
3) Setting “MAX” manifold gas pressure
To enter the Gas Valve Setup mode:
a. Scroll down on the user interface to Unit Test.
b. Scroll to the right and select “Gas Val Setup”.
c. Push the Enter button.
d. Scroll to the right and select MAX; then push the
Enter button.
e. Select “MAX” and push the Enter button.
f. When asked “Are You Sure”, select Yes, and push the
Enter button.
g. The furnace will now begin another ignition se-
quence.
h. If pressure switch 2 & 3 learning routines have not
been performed; after successful ignition, the inducer
will go through this operation. (see Inducer Learning
Routine section).
i. Allow 5 minutes to pass before attempting to adjust
the 100% manifold pressure. This will insure that the
learning routine is complete and that the heat rise is
stable.
j. Read the 100% manifold pressure.
k. If needed, remove the high heat manifold adjustment
cover and adjust to obtain the correct manifold pres-
sure. See Figure 7.
100% (HIGH) HEAT ADJUSTMENT: COUNTER-
CLOCKWISE TO DECREASE MANIFOLD PRESSURE
OR CLOCKWISE TO INCREASE MANIFOLD PRES-
SURE.
l. Use Manifold Pressure Settings Table 1 for the cor-
rect manifold pressure setting in Inches of Water
Column.
m. Replace and tighten the adjustment cover for the
high heat and read the manifold pressure again. This
procedure may need to be repeated until the correct
manifold pressure is obtained.
NOTE: The adjustment cover over the high heat must
be in place during manifold gas pressure readings.
See Figure 6.
n. If the firing rate cannot be obtained with the manifold
pressures specified in Table 1, the orifices must be
changed. If a change of orifices is required to correct
the furnace input rating, refer to Table 17 on page 39
of the Installer's guide.
o. Once the 100% manifold pressure has been adjust-
ed; push the Enter button on the user interface. This
will stop the gas valve setup mode and take you back
to the home screen.
WARNING
!
EXPLOSION HAZARD
REPLACE AND/OR TIGHTEN ALL PLUGS
REMOVED OR LOOSENED WHEN ADJUST-
ING GAS PRESSURE. LEAK CHECK THE
FITTINGS BEFORE PLACING INTO REGU-
LAR SERVICE.
FAILURE TO FOLLOW THIS WARNING
COULD RESULT IN SERIOUS PERSONAL
INJURY, PROPERTY DAMAGE, OR DEATH.
p. Remove all field supplied tubing and measurement
devices. Reinstall and tighten all covers and outlet
pressure tap screw.
q. Leak test all gas fittings using a leak detection solu-
tion or soap suds.
r. Turn comfort control to home owners desired tem-
perature.
PERSONALITY MODULE
The Personality Module is a removable memory device,
on which is stored model specific data required for prop-
er furnace operation. The Personality Module is tethered
to the unit and must remain with the furnace at all times.
The Personality module must remain plugged into the fur-
nace IFC.

UHM-DHM-SF-1V-EN 15
Service Facts
STAND ALONE OPERATION
(CONTINGENCY MODE)
The Contingency Mode allows the installer to set the
equipment to operate in an ON/ OFF Duty Cycle mode.
This mode will be activated using the User Interface.
Contingency Mode is NOT available in 24VAC mode.
The user will select the desired level of capacity
required, Stage 1 (40%) or 2 (100%). The user will
select the desired ON/ OFF Duty Cycle, 10% minimum
to 50% maximum, (10% increments, 10% = 2 minutes
On, 18 minutes Off; 50% = 10 minutes on, 10 minutes
off).
CONTINGENCY MODE
Note:
Stage 1 = 40% (low) heat, Stage 2 = 100% (high) heat
Note:
If a communicating comfort control is detected to be
present and the contingency mode is selected,
NOT AVAILABLE will be displayed on the User
Interface.
•Stand alone operation can only be entered at the
user interface.
• Stand alone operation can be set up to operate the fur-
nace in Heating Only.
• The contingency mode is used when the communi-
cating comfort Control is not communicating with
the furnace or when setting gas manifold pressures.
• Before attempting to enter contingency mode,
disconnect the Data wire "D" from the Furnace IFC ter-
minal block.
•The contingency mode will function only when the
Furnace IFC is not flashing a fault code at its
Fault LED.
•To enter the contingency mode of operation, turn 115
VAC power off. When the Green LED on the variable
speed inducer drive goes out, turn 115 VAC power
back on.
• Scroll down using the down arrow at the User
Interface until you see CNTNGNCY Mode, then
press the Enter button.
•CNTNGNCY MODE and STAGE will now
be displayed. Press the Enter button.
•STAGE and OFF [OFF] will now be displayed.
First or Second heat stage must be select-
ed. Use the orarrows to select the stage
of heat wanted and then push the Enter button
and then the button.
•DUTY CYCLE and 10% [10%] will now be displayed. A
duty cycle must now be selected from 10 to 50%. A
10% duty cycle will run the furnace for 2 minutes and
then off for 18 minutes. A 50% duty cycle will run the
furnace for 10 minutes and then be off for 10 minutes.
These duty cycles will be repeated 3 times per hour.
Use the orarrows to select a duty cycle and then
push the Enter button and then the  button.
•Start and NO [NO] will now be displayed. With a NO/
NO question being asked, use the orarrows to
select the YES and then press the ENTER button.
•Are you Sure and NO [NO] will now be displayed.
With a NO/ NO question being asked, use the or
arrows to select the YES and then press the ENTER
button.
•Turn 115VAC power off. When the Green LED on
the variable speed inducer drive goes out, turn
115 VAC power back on.
•When the furnace is operating in the contingency
mode (stand alone operating cycle), the user inter-
face will display the following information. The top
line will say CNTNGNCY MODE. The bottom line
will show the duty cycle stage number STG (1 or 2)
selected, and the percent number 10-50 % selected.
•All furnace operating controls, pressure switches and
communications between the IFC and the variable
speed inducer drive and the variable speed indoor
blower will be functional during contingency mode
operation of the furnace.
•The  and ENTER buttons do not function in
the contingency mode of operation.
•To exit the contingency mode of operation turn
off the 115 VAC power to the furnace.
•The contingency mode will stop for any of the follow-
ing reasons:
(1) If the furnace IFC receives a signal from the
communicating comfort control. This will only hap-
pen if the data wire "D" from the comfort control has
been reconnected to the furnace IFC terminal board
terminal "D".
(2) Power is removed from the furnace and then
turned back on.
(3) The Furnace IFC enters a RESET mode of op-
eration.
(4) A fault is detected by the furnace IFC. Fault LED
will be flashing an Alert Code.
24V CONTINGENCY MODE
An alternative method for the contingency mode can be
used by changing the mode of operation in the Use
Interface to 24V mode and installing a conventional
24V comfort control.
To set this mode of operation:
Remove all wiring from the *CONT900 comfort control
and install a 24V comfort control. If the comfort
control requires a 24V common; connect R and B
to respective terminals. Connect a third wire to "W".
At the control board, connect the same three wires
to the corresponding terminals. Jumper W1 to W2 at
the control board. The stage delay between W1 and
W2 can be set by scrolling thru the User Interface. It
is factory set to zero minutes but can be adjusted to
5, 10, or 15 minutes.

16 UHM-DHM-SF-1V-EN
Service Facts
IFC INDUCER LEARNING ROUTINE SEQUENCE
Note:
Stage 1 = 40% (low) heat, Stage 2 = 100% (high) heat
•The furnace IFC will go through an inducer learning
routine for three pressure switches.
•The learning routine is done to determine the
correct amount of ventilation air for complete
combustion.
• The inducer motor speed may be different for each
installation due to the different length and size of the
ventilation pipe, exhaust vent pipe, number of pipe
fittings used, and the type of vent cap installed.
• The inducer learning routine is repeated each time
the power to the furnace is interrupted. Once power
is restored and the furnace receives a call for heat,
the PS-1, PS-2 inducer learning routine will be initi-
ated. The furnace IFC will not go through a PS-3 in-
ducer learning routine until it receives a call for 100%
(high) heat.
• To ensure the furnace heating efficiency is maintained
the furnace IFC will repeat the inducer motor learning
routine after :
150 Cycles at 40% (low) heat
100 Cycles at 65% (medium) heat
50 Cycles at 100% (high) heat
PS-1, PS-2 Inducer Learning Routine
•The furnace IFC checks the pressure switches PS-
1, PS-2 and PS-3. They all have to be open before a
heating cycle can begin.
• The furnace IFC sends a digital signal to the
variable speed inducer drive to run the inducer
motor at the preset factory 65% (medium) heat RPM.
• The furnace IFC waits for the PS-1 and PS-2
pressure switches to close. A 24 Volt AC signal is
sent to the furnace IFC when a pressure switch
closes.
• If PS-1 and PS-2 do not close at the preset factory
65% (medium) heat RPM, the furnace IFC will con-
tinue to signal the variable speed inducer drive to
increase the inducer speed in steps until PS-1 and
PS-2 close or until the maximum RPM for 65% (me-
dium) heat is reached.
• When PS-1 and PS-2 switches close, the furnace
IFC will then start the ignition cycle.
• The IFC now starts the igniter warm up cycle.
• Near the end of the warm up cycle the furnace
IFC will turn on the gas valve.
NOTE: The furnace lights at approximately 65% of
capacity.
• When the burner flame is detected by the furnace
IFC, a forty-five second time delay for indoor blower
operation begins. The forty-five second time delay
allows the heat exchanger and the recuperative
cell to warm up.
• The furnace IFC will now start its 65% (medium)
heat inducer learning routine.
• The furnace IFC will signal the variable speed in-
ducer drive beginning to reduce the inducer motor
speed in steps until the furnace IFC detects that
PS-2 is open.
• When PS-2 opens, the furnace IFC will NOTE the
inducer motor RPM.
• The furnace IFC then adds an additional number
of RPM to the 65% (medium) heat inducer motor
NOTED RPM until PS-2 closes.
• The additional number of RPM plus this NOTED
RPM is the learned 65% (medium) heat inducer
operating RPM.
• The furnace IFC now stores this learned operating
inducer RPM for 65% (medium) heat in its memory.
• The furnace IFC will use this stored learned
operating inducer RPM for 65% (medium) heat
calls it receives in the future.
• If the furnace IFC is still receiving a call for
low heat operation it will now start the learning rou-
tine for 40% (low) heat.
• The furnace IFC will then continue to reduce the
inducer motor RPM in steps until the furnace IFC
detects that PS-1 is open.
• When PS-1 opens, the furnace IFC will NOTE the
inducer motor RPM.
• The furnace IFC then adds an additional number of
RPM to the 40% (low) heat inducer motor NOTED
RPM until PS-1 closes.
• The additional number of RPM plus this NOTED
RPM is the learned 40% (low) heat inducer operat-
ing RPM.
• The furnace IFC now stores this learned inducer
operating RPM for 40% (low) heat in its memory.
• The furnace IFC will use this stored learned inducer
operating RPM for 40% (low) heat calls it receives
in the future.
• Whenever the furnace is powered up or after a RE-
SET, the furnace IFC will not go through a learning
routine for 100% (high) heat until it receives a call
for 100% (high) heat.

UHM-DHM-SF-1V-EN 17
Service Facts
PERIODIC SERVICING REQUIREMENTS
WARNING
!
Disconnect power to the unit before removing the
Blower door. Allow a minimum of 10 seconds for IFC
power supply to discharge to 0 volts.
Failure to follow this warning could result in property
damage, personal injury or death.
WARNING
!
CARBON MONOXIDE POISONING HAZARD
Failure to follow the service and/ or periodic
maintenance instructions for the Furnace and venting
system, could result in carbon monoxide poisoning or
death.
1. GENERAL INSPECTION – Examine the furnace
installation annually for the following items:
a. All flue product carrying areas external to the
Furnace (i.e. chimney, vent connector) are clear
and free of obstruction. A vent screen in the end of
the Vent (flue) Pipe must be inspected for blockage
annually.
b. The vent connector is in place, slopes upward
and is physically sound without holes or excessive
corrosion.
c. The return air duct connection(s) is physically
sound, is sealed to the Furnace and terminates
outside the space containing the Furnace.
d. The physical support of the Furnace should be
sound without sagging, cracks, gaps, etc., around
the base so as to provide a seal between the
support and the base.
e. There are no obvious signs of deterioration of the
Furnace.
2. FILTERS – Filters should be cleaned or replaced
(with high velocity filters only), monthly and more
frequently during high use times of the year such as
midsummer or midwinter.
INDOOR BLOWER TIMING
Heating: The Integrated Furnace Control module
controls the Indoor Blower. The Blower
start is fixed at 45 seconds after ignition.
The FAN-OFF period is field selectable
via the User Interface menu at 60, 100,
140, or 180 seconds. The factory setting is
100 seconds.
Cooling: Continuous Fan mode is 50% of the cool-
ing CFM. This is a selectable range on
the Comfort Control menu.
When in communicating mode, see Use Interface Menu
in furnace Installer's Guide.
PS-3 Inducer Learning Routine
Note:
Stage 1 = 40% (low) heat, Stage 2 = 100% (high) heat
• When the furnace IFC receives a digital signal for
100% (high) heat from the comfort control it will begin
the PS-3 inducer learning routine.
• The furnace will start the heating cycle in 65% (medi-
um) heat, if not already on, and then begins the PS-3
inducer learning routine.
• The furnace IFC will send a digital signal to the vari-
able speed inducer drive to run the inducer motor at
the preset factory 100% (high) heat RPM.
• The furnace IFC waits for PS-3 pressure switch to
close. A 24 Volt AC signal is sent to the furnace IFC
when the pressure switch closes.
• If PS-3 does not close at the factory preset 100%
(high) heat RPM, the furnace IFC will continue to sig-
nal the variable speed inducer drive to increase the
inducer speed in steps until PS-3 closes or until the
maximum RPM for 100% (high) heat is reached.
• The furnace IFC enters a time delay so that the heat
exchanger and the recuperative cell warm up to their
high heat operating temperature. At the end of this
time delay, the inducer discharge air temperature
will be at its high heat operating temperature and the
density of the products of combustion will be stabi-
lized.
• The furnace will now signal the variable speed
inducer drive to reduce the inducer speed in steps
until PS-3 opens.
• When PS-3 opens, the furnace IFC will NOTE the in-
ducer motor RPM.
• The furnace IFC then adds an additional number of
RPM to the 100% (high) heat inducer motor NOTED
RPM until PS-3 closes.
• The furnace IFC now stores this learned inducer oper-
ating RPM for 100% (high) heat in its memory.
• The furnace IFC will use this stored learned inducer
operating RPM for 100% (high) heat calls it receives
in the future.
• If PS-3 is not closed when the inducer reaches its
maximum RPM, the furnace IFC will signal the vari-
able speed inducer drive to reduce the inducer Motor
speed in steps to its low heat LEARNED SPEED.
• The furnace IFC flashes its Red Fault LED three
times repeatedly. The furnace IFC will keep
operating at low heat for 10 minutes and then retry
the PS-3 learning routine.

18 UHM-DHM-SF-1V-EN
Service Facts
3. BLOWERS – The Blower size and speed determine
the air volume delivered by the Furnace. The Blower
motor bearings are factory lubricated and under
normal operating conditions do not require servicing.
Annual cleaning of the Blower wheel and housing is
recommended for maximum air output, and this must
be performed only by a qualified servicer or service
agency.
4. IGNITER – This unit has a special hot surface direct
ignition device that automatically lights the burners.
Please note that it is very fragile and should be
handled with care.
CAUTION
!
Do NOT touch igniter. It is extremely hot.
5. BURNER – Gas burners do not normally require
scheduled servicing, however, accumulation of
foreign material may cause a yellowing flame or
delayed ignition. Either condition indicates that a
service call is required. For best operation, burners
must be cleaned annually using brushes and vacuum
cleaner.
Turn off gas and electric power supply. To clean
burners, remove Burner Box cover (6 to 8 screws)
and top burner bracket. Lift burners from orifices.
NOTE:
Be careful NOT to break igniter when removing
burners.
Clean burners with brush and/ or vacuum cleaner.
Reassemble parts by reversal of the above
procedure. The Burner Box must be resealed when
replacing box cover.
NOTE:
Natural gas units should not have any yellow tipped
flames. This condition indicates that a service call is
required. For best operation, burners must be cleaned
annually using brushes and vacuum cleaner.
NOTE:
On LP (propane) units, due to variations in BTU content
and altitude, servicing may be required at shorter
intervals.
6. HEAT EXCHANGER/ FLUE PIPE – These items
must be inspected for signs of corrosion, and/
or deterioration at the beginning of each heating
season by a qualified service technician and cleaned
annually for best operation. To clean flue gas
passages, follow recommendations below:
a. Turn off gas and electric power supply.
b. Inspect flue pipe exterior for cracks, leaks, holes
or leaky joints. Some discoloration of PVC pipe is
normal.
c. Remove burner compartment door from Furnace.
d. Inspect around insulation covering flue collector
box. Inspect induced draft Blower connections
from recuperative cell and to the flue pipe
connection.
e. Remove burners. (See 5. Burner)
f. Use a mirror and flashlight to inspect interior of
Heat Exchanger, be careful not to damage the
Igniter, Flame Sensor or other components.
g. If any corrosion is present, the Heat Exchanger
should be cleaned by a qualified service
technician.
h. After inspection is complete replace Burner Box
cover, burners, and Furnace door.
i. Restore gas supply. Check for leaks using a soap
solution. Restore electrical supply. Check unit for
normal operation.
7. COOLING COIL CONDENSATE DRAIN - If a cooling
coil is installed with the Furnace, condensate drains
should be checked and cleaned periodically to
assure that condensate can drain freely from coil
to drain. If condensate cannot drain freely water
damage could occur. (See Condensate Drain in
Installer’s Guide.)

UHM-DHM-SF-1V-EN 19
Service Facts
*UHM WIRING DIAGRAM
CAUTION
!
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and dangerous
operation. Verify proper operation after servicing.

20 UHM-DHM-SF-1V-EN
Service Facts
*UHM SCHEMATIC DIAGRAM
CAUTION
!
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and dangerous
operation. Verify proper operation after servicing.