Honeywell ST7997 User Manual
ST7997
Oil Burner Mounted Electric Fan Timer
INSTALLATION INSTRUCTIONS
APPLICATION
The ST7997 Oil Burner Mounted Electric Fan Timer
integrates control of burner and circulator fan operations in
an oil furnace and is the central wiring point for most
electrical components in the furnace. The ST7997 mounts
on a standard four-inch by four-inch junction box typically
located on the oil burner. When used with the R7997
Integrated Oil Primary Controller and Ignitor, it provides
simplified wiring and field serviceability. The basic
purposes of the ST7997 are to monitor the thermostat for
heat, cool and fan demands, run the oil burner primary
control and run a two-speed circulating fan, as required.
The ST7997 also monitors a limit switch string that
energizes the circulating fan when the limit switch opens.
The ST7997 provides electronic air cleaner (EAC) and
humidifier (HUM) terminal connections for field installation
convenience.
SPECIFICATIONS
Electrical
Input Ratings
Supply Voltage:
102 to 132 Vac (120 Vac nominal), 60 Hz.
Supply Current:
100 mA maximum without loads connected to outputs.
20A maximum with loads connected to outputs.
Output Ratings:
Relay Contacts:
Circulator Heat or Cool Blower Speed Rating: 15A Full
Load Amperage (FLA) (0.75 pF)/30A Locked Rotor
Amperage (LRA) (0.5 pF).
NOTE: FLA rating is reduced by EAC load.
EAC:
1A maximum.
Circulator Continuous Blower Speed Rating:
8A FLA (0.75pF)/16A LRA (0.5pF).
Humidifier:
1A maximum.
Limit:
10A maximum.
L1/L2 (Burner):
20A maximum.
Thermostat Current:
Heat Mode: 100 mA (R7997 supplied).
Cool Mode: Cooling contactor load 500 mA maximum
(ST7997 supplied).
Cooling Contactor:
2 VA minimum, 12 VA maximum.
Molex® is a registered trademark of Molex Incorporated.
Fuse:
1A (automotive type ATO).
Delay Timings:
Heat On Delay: 45 or 60 seconds (fixed or field
selectable via DIP switch optional position 3).
Heat Off Delay: 60/100/120/150 seconds (four field
selections via DIP switch positions 1 and 2).
Cool On/Off Delay: 0/0 or 30/30 seconds (fixed).
Delay Timing Tolerances:
±5 seconds or ±20 percent, whichever is greater.
Environmental
Temperature Ranges:
Operating: -40°F (-40°C) to +150°F (66°C).
Storage: -20°F (-29°C) to +150°F (66°C).
Humidity:
90 percent relative humidity at 95°F (35°C),
noncondensing.
Approvals:
Underwriters Laboratories Inc. Component
Recognized: File 353.
Canadian Underwriters Laboratories inc. Component
Recognized: Pending approval.
Mechanical:
Dimensions (Fig. 1):
4-9/32 in. (109 mm) long by 4-1/4 in. (108 mm) wide by
3-27/32 (97 mm) high. See Fig. 1.
Molex® is a registered trademark of Molex Incorporated.
Copyright © 1998 Honeywell Inc. • All Rights Reserved
X-XX UL
69-1204
ST7997 OIL BURNER MOUNTED ELECTRIC FAN TIMER
4-1/4
(108)
WARNING
Electrical Shock Hazard
Can cause serious injury or death.
Disconnect power supply before wiring to prevent
electrical shock or equipment damage.
C
YGRc
4-9/32 (109)
3-27/32
(97)
Fig. 1. ST7997A,B Oil Burner Mounted Electric Fan
Mounting:
Mounts directly on standard 4 in. (102 mm) by 4 in.
(102 mm) junction box.
Packaging:
Unit pack and bulk pack.
Connections:
R7997, Oil Burner Motor, Oil Valve and Power (L1, L2):
Circulator Blower (Neutral, Heat, Cool, Continuous),
Humidifier: Two 1/4 in. (6 mm) by 1/32 in. (0.8 mm)
Electronic Air Cleaner: Two 1/4 in. (6 mm) by 1/32 in.
Thermostat/Cooling Contactor: Four No. 4 screw
Timer dimensions in in. (mm).
Six (6) 1/4 in. (6 mm) by 1/32 in. (0.8 mm) quick
connects pass through recessed cover on bottom of
case.
Limit (Hot, Limit): One six-position Molex® in-line
connector flush with top of case or six 1/4 in. (6 mm)
by 1/32 in. (0.8 mm) quick connects individually
recessed in top of case.
quick connects individually recessed in top of case.
(0.8 mm) quick connects individually recessed in top
of case.
terminals marked Rc, Y, G and C on front side of
case.
INSTALLATION
Location and Mounting
Mount the ST7997 on the oil burner 4 in. (102 mm) by 4 in.
(102 mm) junction box compartment using four No. 6
screws (obtained locally). See Fig. 2.
ST7997R7997
M12920
BURNER
Fig. 2. ST7997A,B Oil Burner Mounted Electric Fan
IMPORTANT
Timer typical installation.
The ST7997 requires a mechanical or electronic
(power-stealing or battery-powered) five-wire
thermostat with independent heat/cool circuits
(R, W, Rc, Y, G).
Wiring
All wire must comply with local codes and ordinances.
Refer to Fig. 3 for standard wiring connections and Fig. 4
for units with pre- and post purge.
Make wiring connections within the oil burner junction box
for applications requiring power-venting. Add a 4 in. by
4 in. (102 mm by 102 mm) junction box, at least 1/2 in.
(13 mm) deep between the ST7997 and the oil burner
junction box. See Fig. 5 for wiring diagram showing airflow
switch and power vent motor.
M12919
When Installing this Product...
1. Read these instructions carefully. Failure to follow
them can damage the product or cause a hazardous
condition.
2. Check the ratings and specifications given in the
instructions and on the product to make sure the
product is suitable for your application.
3. Installer must be a trained, experienced service
technician.
4. After installation is complete, check out the product
operation as provided in these instructions.
69-1204
2
ST7997 OIL BURNER MOUNTED ELECTRIC FAN TIMER
TT
R7997
INTEGRATED
OIL PRIMARY
WITHOUT
BLOWER DELAY
BLACK
ORANGE
WHITE
BURNER
MOTOR
HUMIDIFIER EAC
N
N
HUM
L2
BURNER/
VALVE
EAC
LIMIT
(LINE
VOLTAGE)
FURNACE
OIL
PRIMARY
LIMIT
L1
N
N
ISOLATION
L1
1K2
HI
1K1
L2
COOL
CIRCULATOR
BLOWER
MED LO
LO
HEAT
2K2
CONTINUOUS
2K1
F1
C
HEAT CALL
LIMIT
CONTROL
ELECTRONICS
K1 K2
RC
J-BOX
G
Y
OEFT
ST7997
MED HI
WIRES
UNUSED
RC
C
G
Y
SCREW TERMINAL
1/4 IN. QUICK CONNECT
R
W
RC
G
Y
THERMOSTAT
5-WIRE
COMPRESSOR
CONTACTOR
Fig. 3. ST7997 Oil Burner Mounted Electronic Fan Timer standard wiring connections.
L2
L1
GND
M12924
3
69-1204
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