Comfortaire Century GDD95C Series User manual

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SERVICE MANUAL
GDD95C
(P) 508115-01
*P508115-01*
Table of Contents
Technical Specifications - GDD95C ............................2
Parts Arrangement.......................................................5
Electrical......................................................................6
Placement & Installation............................................20
Joint Cementing Procedure.......................................21
Venting Practices.......................................................22
Vent Piping Guidelines ..............................................23
Condensate Piping ....................................................39
Start-Up .....................................................................41
Heating System Service Checks ...............................42
Typical Operating Characteristics..............................46
Maintenance..............................................................49
Wiring Diagram..........................................................50
Troubleshooting: Heating Sequence of Operation ....51
Troubleshooting: Heating Sequence of Operation
(Continued)................................................................52
Troubleshooting: Cooling Sequence of Operation.....53
Troubleshooting: Continuous Fan / Accessories
Sequence of Operation..............................................54
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

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Technical Speci ications - GDD95C
MODEL NUMBER GUIDE
REV CODE
REVISION
NOM. CFM X 100
2 TON ADD ON COOLING
3 TON ADD ON COOLING
4 TON ADD ON COOLING
5 TON ADD ON COOLING
CABINET WIDTH
A = 14.5” WIDTH
B = 17.5” WIDTH
C = 21.0” WIDTH
D = 24.5” WIDTH
BTUH INPUT
HEATING INPUT X 1000
GAS
G = GAS FURNACE
CONFIGURATION
DD = DOWNFLOW
AFUE
80 = 80% EFFICENCY
92 = 92% EFFICENCY
95 = 95% EFFICENCY
G DD 95 CG DD 95 C 004455BB3 M3 M
STAGES/MOTOR
A = SINGLE STAGE PSC
C = SINGLE STAGE CONSTANT TORQUE
T = TWO STAGE VARIABLE SPEED ECM
PHYSICAL AND ELECTRICAL DATA
Model
Input
(Btuh)
Output
(Btuh)
AFUE
(ICS)
%
Nom.
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.)
DOWNFLOW
GDD95C045B3M 44,000 42,000 95.0% 1-1/2 — 3 1/2 120 - 60 - 1 15 6.8 40 131
GDD95C070B4M 66,000 64,000 95.0% 2-1/2 — 4 1/2 120 - 60 - 1 15 8.4 40 144
GDD95C090C4M 88,000 85,000 95.0% 2-1/2 — 4 1/2 120 - 60 - 1 15 8.4 40 160
GDD95C110C5M 110,000 106,000 95.0% 3 — 5 1/2 120 - 60 - 1 15 10.9 40 174

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Model
Motor
Size (hp)
Blower
Size
Temp
Rise (F°)
Blower
Speed
CFM @ external static pressure - " w.c.
.20 .30 .40 .50 .60 .70 .80
DOWNFLOW
GDD95C045B3M 1/2 10 x 8 25 - 55
High 1320 1285 1275 1230 1185 N/A N/A
Med/High 1215 1165 1150 1095 1060 1020 980
Med 1090 1065 1025 985 935 915 860
Med/Low 825 795 750 705 655 590 555
Low 785 735 705 650 605 545 485
GDD95C070B4M 3/4 11½ x 10 25 - 55
High 1705 1665 1605 1585 1540 N/A N/A
Med/High 1470 1430 1390 1335 1300 1260 1220
Med 1265 1235 1185 1155 1100 1050 1015
Med/Low 1165 1120 1070 1015 970 915 865
Low 895 835 775 690 625 570 520
GDD95C090C4M 3/4 10 x 10 40 - 70
High 1685 1630 1620 1570 1540 N/A N/A
Med/High 1455 1415 1370 1335 1295 1260 1210
Med 1310 1285 1245 1185 1145 1110 1060
Med/Low 1220 1165 1125 1080 1045 990 940
Low 1080 1035 985 925 875 825 760
GDD95C110C5M 1 11 x 11 40 - 70
High 2185 2150 2085 2060 2005 1970 1910
Med/High 1910 1850 1810 1765 1700 1665 1620
Med 1720 1670 1605 1565 1510 1460 1420
Med/Low 1575 1525 1465 1420 1370 1325 1275
Low 1360 1290 1255 1190 1160 1100 1045
BLOWER PERFORMANCE DATA

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PART NUMBER DESCRIPTION
External Filter Rack kits
1.841018 1 pack (16 x 25)
1.841039 10 pack (16 x 25)
Natural to LP Kits
11K50 1-Stage - 90
11K45 High Altitude 1-Stage
13X57 30k BTUH
Return Air Base
68W62 17.5" B Width
68W63 21.0" C Width
68W64 24.5" D Width
Downow Combustible Flooring Base
11M60 17.5” B Width
11M61 21.0” C Width
Night Service Kits
86W57 Single Stage
Horizontal Suspension Kit
51W10 80% & 90% Kit
Flush Mount Termination (90% Furnaces only) US Only
51W11 2" & 3" Vent Version
Concentric Vent Kit (90% Furnaces only) US Only
71M80 1-1/2" Vent Version
69M29 2" Vent Version
60L46 3" Vent Version
Concentric Vent Kit (90% Furnaces only) Canada
44W92 1-1/2" and 2" Vent Version
44W93 3" Vent Version
2-Stage Compressor Relay Kit
85W66 Blower Relay Kit
Twinning Kit
16W72 Constant Torque Gas Furnace Twinning Kit
For vent length and clearances to combustibles, please reference
installation instructions.
ACCESSORY LIST

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Parts Arrangement
Figure 1.
CONTROL BOX
(Includes integrated control,
transformer and door switch)
BAG ASSEMBLY
BLOWER MOTOR
(hidden)
COMBUSTION
AIR INDUCER
BURNER BOX ASSEMBLY
(includes flame sensor, rollout switches and ignitor)
GAS VALVE
BLOWER DECK
HEAT EXCHANGER
COLD END HEADER BOX
PRIMARY LIMIT
BLOWER
ACCESS PANEL
HEATING
ACCESS PANEL
COMPARTMENT
COMPARTMENT

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Electrical
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
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
GDD95C unit components are shown in Figure 1. The
combustion air inducer, gas valve and burners can be
accessed by removing the outer access panel. The
blower and control box can be accessed by removing the
blower access panel.
Control Box Components (Figure 2)
Unit transformer (T1) and integrated ignition control
(A92) are located in the control box. In addition, a door
interlockswitch (S51) is located in the control box.
Integrated Control
Door Interlock
Switch
Transformer
Circuit Breaker
Figure 2. Control Box
Transformer (T1)
A transformer located in the control box provides power
to the low voltage section of the unit. The transformers on
all models are rated at 40VA with a 120V primary and 24V
secondary.
Door Interlock Switch (S51)
A door interlock switch rated 14A at 120VAC is located
on the control box. The switch is wired in series with line
voltage. When the blower door 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 at 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.
Integrated Ignition Control (A92)
Shock hazard.
Disconnect power before servicing.
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
The hot surface ignition control system consisting of
an integrated control (Figure 3 with control terminal
designations in Table 1 through Table 3), sensor and
ignitor (Figure 5). The integrated control and ignitor work
in combination to ensure furnace ignition and ignitor
durability. The integrated control, controls all major furnace
operations. The integrated control also features a RED
LED for troubleshooting and two accessory terminals rated
at (1) one amp. See Table 4 or Table 5 for troubleshooting
diagnostic codes. The nitride ignitor is made from a non-
porous, high strength proprietary ceramic material that
provides long life and trouble free maintenance.
Pin # Function
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
Table 1. 4-Pin Terminal Designations
Pin # Function
1High Limit Output
2Not Used
3 24V Line
4Not Used
5Rollout Switch Out
624V Neutral
7High Limit Input
8Ground
9 Gas Valve Common
10 Pressure Switch In
11 Rollout Switch In
12 Gas Valve Out
Table 2. 12-Pin Terminal Designations

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1/4” Quick Connect Terminals
120HUM Humidier 120VAC
LINE 120VAC
XFMR Transformer 120VAC
CIRC Indoor Blower 120VAC
EAC Indoor Air Quality Accessory 120VAC
NEUTRALS Common 120VAC
HUM24 Humidier 24VAC
3/16” Quick Connect Terminals
COOL Cooling Tap 24VAC
HEAT Heating Tap 24VAC
FAN Continuous Blower 24VAC
PARK (no power) Park terminal for unused speed taps
FS Flame Sense
24 COM Common 24VAC
Table 3.
The integrated control is equipped with an LED light for troubleshooting. The diagnostic codes are listed in Table 4 or Table
5.
Red LED Flash Code2Diagnostic Codes / Status of Furnace
O󰀨 No power to control or board fault detected
Heartbeat1Control powered - displayed during all modes of operation if no errors are detected
1Reverse Line Voltage Polarity
2Improper Earth Ground
3Burner failed to light, or lost ame during heat demand
4Low Flame Signal - check ame sensor
5Watchguard - burner failed to light, exceeded maximum number of retries or recycles
6Not Used
7Primary or Secondary Limit Open or Watchguard Mode - Limit Switch Open longer than 3 minutes
8Rollout Switch Open
9 Pressure Switch failed to close or opened during heat demand
10 Watchguard - Pressure Switch opened 5 times during one heat demand
11 Pressure Switch stuck closed prior to activation of combustion air inducer
12 Flame Sensed without gas valve energized
13 Low Line Voltage
1 A ”Heartbeat” is indicated by a ”Slow Flash” - 1 sec on 1 sec o󰀨, repeating
2 Error codes are indicated by a ”Rapid Flash” - the LED ashes X times at 1/2 sec on 1/2 sec o󰀨, remains o󰀨 for 3 sec, then repeats
NOTE: Last 10 error codes are stored in memory including when power is shut o󰀨 to the unit. - To recall, press and release button,
most recent will be displayed rst, LED o󰀨 for 3 sec, then next error code is displayed, etc. To clear error codes, depress and
hold button longer than 5 seconds.
Table 4. -02 Control Diagnostic Codes

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Red LED Flash Code2Diagnostic Codes / Status of Furnace
O󰀨 No power to control or board fault detected
Heartbeat1Normal Operation - Idle, Continuous Fan, Cool
Continuous Rapid Flash Call for Heat / Burner Operation
1Reverse Line Voltage Polarity
2Improper Earth Ground
3Burner failed to light, or lost ame during heat demand
4Low Flame Signal - check ame sensor
5Watchguard - burner failed to light, exceeded maximum number of retries or recycles
6Not Used
7Primary or Secondary Limit Open or Watchguard Mode - Limit Switch Open longer than 3 minutes
8Rollout Switch Open
9 Pressure Switch failed to close or opened during heat demand
10 Watchguard - Pressure Switch opened 5 times during one heat demand
11 Pressure Switch stuck closed prior to activation of combustion air inducer
12 Flame Sensed without gas valve energized
13 Low Line Voltage
1 A ”Heartbeat” is indicated by a ”Slow Flash” - 1 sec on 1 sec o󰀨, repeating
2 Error codes are indicated by a ”Rapid Flash” - the LED ashes X times at 1/2 sec on 1/2 sec o󰀨, remains o󰀨 for 3 sec, then repeats
NOTE: Last 10 error codes are stored in memory including when power is shut o󰀨 to the unit. - To recall, press and release button,
most recent will be displayed rst, LED o󰀨 for 3 sec, then next error code is displayed, etc. To clear error codes, depress and
hold button longer than 5 seconds.
Table 5. -03 Control Diagnostic Codes

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Figure 3. Integrated Control
(Automatic Hot Surface Ignition System)
BLOWER OFF DELAY
RED LED RECALL BUTTON
Electronic Ignition
On a call for heat the integrated control monitors the
combustion air inducer pressure switch. The control board
will not begin the heating cycle if the pressure switch is
closed (by-passed). Once the pressure switch is determined
to be open, the combustion air inducer is energized. When
the di󰀨erential in the pressure switch is great enough, the
pressure switch closes and a 15-second pre-purge begins.
If the pressure switch is not proven within 2-1/2 minutes,
the integrated control goes into Watchguard-Pressure
Switch mode for a 5-minute re-set period.
After the 15-second pre-purge period, the ignitor warms
up for 20 seconds during which the gas valve opens at
19 seconds for a 4-second trial for ignition. The ignitor
remains energized for the rst 3 seconds during the 4
second trial. If ignition is not proved during the 4-second
period, the integrated 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 integrated control goes into Watchguard-
Flame Failure mode. After a 60-minute reset period, the
integrated control will begin the ignition sequence again.
Fan Time Control
Heating Fan On Time
The fan on time of 30 seconds is not adjustable.
Heating Fan O󰀨 Time
Fan o󰀨 time (time that the blower operates after the heat
demand has been satised) can be adjusted by moving
the jumper to a di󰀨erent setting. The unit is shipped with
a factory fan o󰀨 setting of 90 seconds. For customized
comfort, monitor the supply air temperature once the heat
demand is satised. Note the supply air temperature at the
instant the blower is de-energized.
Adjust the fan-o󰀨 delay to achieve a supply air temperature
between 90° - 110° at the instant the blower is de-energized.
(Longer delay times allow for lower air temperature, shorter
delay times allow for higher air temperature). See Figure 4.
Cooling Fan On Time
The fan on time is 2 seconds and is not adjustable.
Cooling Fan O󰀨 Time
The control has a 45 second fan o󰀨 delay after cooling
demand has been met. This delay is factory set and not
adjustable.
HEAT FAN‐OFF TIME IN SECONDS
To adjust fan-off timing, reposition jumper across pins to
achieve desired setting.
NO JUMPER
60 90
120
180
60 90
120
180
60 90
120
180
60 90
120
180
60 Second
off Time
90 Second
off Time
120 Second
off Time
180 Second
off Time
JUMPER POSITION HEAT OFF
DELAY
PIN 1
PIN 2
PIN 3
PIN 4 PIN 5
60
90
120
180
PIN 2
PIN 3
PIN 4
180
Figure 4.
Heating Components
Combustion air inducer (B6), primary limit control (S10),
ignitor, burners, ame rollout switch (S47), gas valve
(GV1), combustion air pressure switch (S18), and heat
exchangers are located in the heating compartment. The
heating compartment can be accessed by removing the
outer access panel.
Ignitor (Figure 5)
GDD95C units use a nitride ignitor made from a
proprietary ceramic material. To check ignitor, measure
its resistance and voltage. A value of 39 to 70
ohms indicates a good ignitor. Voltage to the ignitor
should be 102 - 132VAC. See Figure 9 for resistance
and voltage checks.

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Figure 5. Burner Box Assembly
Gas Valve
Burner Box Front
Rollout Switch(s)
Flame Sensor
Ignitor
Burner Assembly
Flame Rollout Switches (Figure 5)
Flame rollout switches S47 are SPST N.C. high temperature
limits located on the left and right of the front buner box
plate. S47 is wired to the burner ignition control A92. When
either of the switches sense ame rollout (indicating a
blockage in the combustion passages), the ame rollout
switch trips, and the ignition control immediately closes
the gas valve. Switch S47 in all GDD95C units is
factory preset to open at 210 F + 12 F (99 C + 6.7 C)
on a temperature rise. All flame rollout switches are
manual reset. See flash code 8 in Table 4 or Table 5 for
troubleshooting.
Flame Sensor (Figure 5)
A ame sensor is located on the left side of the burner
support. The sensor is mounted on the front burner box
plate and the tip protrudes into the ame envelope of the
leftmost burner. The sensor can be removed for service
(use steel wool only to clean) without removing any part of
the burners. During operation, ame is sensed by current
passed through the ame and sensing electrode. The
ignition control allows the gas valve to remain open as long
as flame signal is sensed.
NOTE: The GDD95C is polarity sensitive. Make sure
that the furnace is wired correctly and is properly grounded.
A microamp DC meter is needed to check the ame signal
on the integrated control.
Flame (microamp) signal is an electrical current which
passes from the integrated control to the sensor during
unit operation. Current passes from the sensor through the
ame to ground to complete a safety circuit.
Heat Exchanger (Figure 6)
GDD95C units use an aluminized steel primary and
stainless steel secondary heat exchanger assembly.
Heat is transferred to the air stream from all surfaces of
the heat exchanger. The shape of the heat exchanger
ensures maximum efficiency.
The combustion air inducer pulls fresh air through the
burner box. This air is mixed with gas in the burners. The
gas / air mixture is then burned at the entrance of each
clamshell. Combustion gases are then pulled through the
primary and secondary heat exchangers and exhausted
out the exhaust vent pipe.