Carrier | 38GXC | Instruction manual | Carrier 38GXC Instruction manual

40GXC / 38GXC
40GXQ / 38GXQ
High---Wall Duct Free Split Systems
Size 9k, 12k, 18k, and 24k
Installation Instruction
NOTE: Read the entire instruction manual before starting the installation.
TABLE OF CONTENTS
PAGE
PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
SAFETY CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . 3
SYSTEM REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . 3
DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
9k & 12k
CLEARANCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
INSTALLATION GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
INDOOR UNIT INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . 6
OUTDOOR UNIT INSTALLATION . . . . . . . . . . . . . . . . . . 7 -- 8
SYSTEM VACUUM AND CHARGE . . . . . . . . . . . . . . . . . . . . 9
18k & 24k
START--UP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
PARTS LIST
Part
No.
1
2
3
Name of Part
Qty
Mounting Plate
Mounting Screw ST4.2X25TA
Remote Control
1
5
1
1
38/40GXC(Q)
2
A08274
18k & 24k Display Close Up
RUN
INFRARED SIGNAL
RECEPTOR
DEHUMIDIFY MODE
HEAT INDICATOR
COOL INDICATOR
TEMPERATURE
Front Panel
3
9k & 12k Display Close Up
SIGNAL
RECEIVING
WINDOW
DEHUMIDIFY
RUN
TEMPERATURE
HEAT
COOL
Remote
Control
Drain Hose
Connecting Pipe
and Connecting Wires
A09663
Fig. 1 --- 38GXC(Q) / 40GXC(Q) 009, 012, 018 and 024 Parts List
2
SAFETY CONSIDERATIONS
GENERAL
Installing, starting up, and servicing air--conditioning equipment
can be hazardous due to system pressures, electrical components,
and equipment location (roofs, elevated structures, etc.).
Only trained, qualified installers and service mechanics should
install, start--up, and service this equipment.
Untrained personnel can perform basic maintenance functions such
as cleaning coils. All other operations should be performed by
trained service personnel.
When working on the equipment, observe precautions in the
literature and on tags, stickers, and labels attached to the
equipment.
Follow all safety codes. Wear safety glasses and work gloves. Keep
quenching cloth and fire extinguisher nearby when brazing. Use
care in handling, rigging, and setting bulky equipment.
Read these instructions thoroughly and follow all warnings or
cautions included in literature and attached to the unit. Consult
local building codes and current editions of the National Electrical
Code ( NEC ) NFPA 70. In Canada, refer to current editions of the
Canadian electrical code CSA 22.1.
These instructions cover the installation, start--up and servicing of
38GXC(Q) outdoor and 40GXC(Q) indoor units duct free systems.
SYSTEM REQUIREMENTS
Allow sufficient space for airflow and servicing unit. See Fig. 2
and 3 for minimum required distances between unit and walls or
ceilings.
Piping
IMPORTANT: Both refrigerant lines must be insulated
separately.
S Minimum refrigerant line length between the indoor and outdoor
units is 10 ft. (3 m).
S The following maximum lengths are allowed:
WARNING
!
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Before installing, modifying, or servicing system, main
electrical disconnect switch must be in the OFF
position. There may be more than 1 disconnect switch.
Lock out and tag switch with a suitable warning label.
!
CAUTION
35 (11)
50 (15)
50 (15)
35 (11)
50 (15)
50 (15)
S The following are the piping sizes.
Unit Size
9, 12 & 18K
24K
PIPE SIZES
Mix Phase
1/4”
3/8”
Vapor
1/2”
5/8”
Refrigerant Charge
Unit Size
9K
12 K
18 K
24 K
REFRIGERANT CHARGE
Amount of Charge lb. (kg)
2.65 (1.2)
2.8 (1.27)
3.5 (1.6)
5.4 (2.5)
S Above charge is for piping runs up to 25 ft. (7.6 m).
S For piping runs greater than 25 ft. (7.6 m), add 0.1 oz. of
refrigerant per foot of extra piping up to the allowable
length.
S Capillary tubes are used as metering devices.
Connecting (Power and Control Cable)
S The main power is supplied to the outdoor unit. The field
supplied connecting cable from the outdoor unit to indoor unit
consists of four wires and provides the power for the indoor unit
as well as the communication signal and ground between the
outdoor and indoor unit.
Two wires are high voltage AC power, one is low voltage and
one is a ground wire.
S Consult local building codes, NEC (National Electrical Code) or
CEC (Canadian Electrical Code) for special requirements.
Model Size
EQUIPMENT DAMAGE HAZARD
Power Source
9K
12 K
12 K
18 K
24 K
Failure to follow this caution may result in equipment
damage or improper operation.
Do not bury more than 36 in. (914 mm) of refrigerant pipe
in the ground. If any section of pipe is buried, there must be
a 6 in. (152 mm) vertical rise to the valve connections on
the outdoor units. If more than the recommended length is
buried, refrigerant may migrate to the cooler buried section
during extended periods of system shutdown. This causes
refrigerant slugging and could possibly damage the
compressor at start--up.
65 (20)
80 (25)
100 (30)
115 --115 --208/230
208/230
208/230
1
1
-------
----1
1
1
60
60
--- 60
--- 60
--- 60
MIN CKT AMP
MAX FUSE/CB
AMP
20/25
20/25
10/15
14/25
16/30
S Connecting Cable: Voltage drop on the connecting cable
should be kept to a minimum. Do not use thermostat wire. Use
cable size and max length below:
18 AWG
16 AWG
14 AWG
3
50 Feet (16 m)
65 Feet (19.8 m)
>65 Feet (19.8 m)
38/40GXC(Q)
9 & 12K
18K
24K
!!
.
Recognize safety information. This is the safety--alert symbol
When you see this symbol on the unit and in instructions or
manuals, be alert to the potential for personal injury.Understand
these signal words: DANGER, WARNING, and CAUTION.
These words are used with the safety--alert symbol. DANGER
identifies the most serious hazards which will result in severe
personal injury or death. WARNING signifies hazards which
could result in personal injury or death. CAUTION is used to
identify unsafe practices which may result in minor personal injury
or product and property damage. NOTE is used to highlight
suggestions which will result in enhanced installation, reliability, or
operation.
REFRIGERANT LINE LENGTHS ft. (m)
Max Elevation
Max Elevation
Max Line Length
(ID over OD)
(OD over ID)
Unit Size
DIMENSIONS -- INDOOR
H
D
W
A08289
Unit Size
38/40GXC(Q)
9k
12k
18k
24k
W
In. (mm)
30.3 (770)
32.7 (830)
32.7 (830)
42.9 (1090)
H
In. (mm)
9.8 (250)
11.2 (285)
11.2 (285)
13.0 (330)
D
In. (mm)
7.84 (1.99)
8.9 (225)
8.1 (206)
8.2 (208)
Net Operating Weight
Lbs. (Kg)
18.7 (8.50)
24.2 (11.0)
26.4 (12.0)
38.5 (17.5)
DIMENSIONS - OUTDOOR
W
D
H
A08290
Unit Size
9k & 12k
18k
24k
W
In. (mm)
33.4 (848)
33.3 (846)
37.4 (950)
D
In. (mm)
12.6 (320)
11.8 (300)
16.5 (420)
4
H
In. (mm)
21.3 (541)
27.0 (685)
33.1 (840)
Net Operating Weight
Lbs. (Kg)
88.0 (40)
114.4 (52)
140.3 (64)
CLEARANCES -- INDOOR
CEILING
6" (0.15m) min.
5"
(0.13m)
min.
5"
(0.13m)
min.
6' (1.8m)
38/40GXC(Q)
FLOOR
A07891
Fig. 2 --- Indoor unit clearance
CLEARANCES - OUTDOOR
A
Air-inlet
E
D
B
C
Air-outlet
A07894
UNIT
A
B
C
D
E
12k in. (mm)
20 (508)
20 (508)
24 (610)
12 (305)
12 (305)
Fig. 3 --- Outdoor Unit Clearance
5
10.1 (256)
25.6 (650.5)
A09664
Fig. 6 --- 18k Mounting Plate Spacing
11.4 (290)
Ideal installation locations include:
Indoor Unit
S A location where there are no obstacles near inlet and outlet area.
S A location which can bear the weight of indoor unit.
S Do not install indoor units near a direct source of heat such as
direct sunlight or a heating appliance.
S A location which provides appropriate clearances as outlined in
Fig. 2 (pg. 5).
Outdoor Unit
S A location which is convenient to installation and not exposed to
strong wind. If unit is exposed to strong winds it is
recommended that a wind baffle be used. Contact your Carrier
Representative for drawings. (See Fig. 11, pg. 7)
S A location which can bear the weight of outdoor unit and where
the outdoor unit can be mounted in a level position.
S A location which provides appropriate clearances as outlined in
Fig. 3 (pg. 5).
S Do not install the indoor or outdoor units in a location with
special environmental conditions. For those applications, contact
your Carrier Representative.
INDOOR UNIT INSTALLATION
A09665
Fig. 7 --- 24k Mounting Plate Spacing
INSTALL MOUNTING PLATE
1. Carefully remove the mounting plate, which is attached to
the back of the indoor unit.
2. The mounting plate should be located horizontally and level
on the wall. All minimum spacings shown in Fig. 4
through Fig. 7 should be maintained.
3. If the wall is block, brick, concrete or similar material, drill
.2” (5 mm) diameter holes and insert anchors for the appropriate mounting screws.
4. Attach the mounting plate to the wall.
Refrigerant Line Routing
The refrigerant lines may be routed in any of the four directions
shown in Fig. 8 (a) and (b).
For maximum serviceability, it is recommended to have refrigerant
line flare connections and the drain connection on the outside of
the wall that the fan coil is mounted on.
4.09 (104)
.52 (13)
.08 (2)
2.64 (67)
DRILL HOLE IN WALL FOR INTERCONNECTING
PIPING, DRAIN AND WIRING
As viewed from front
Knockout 3
8.58 (218)
38/40GXC(Q)
INSTALLATION GUIDE
Knockout 2
3
1 Right Exit
.04 (1)
2 Right Rear Exit
(a)
4
Knockout 1
Left Exit
Left Rear Exit
(b)
(c)
A08281
Fig. 8 --- Refrigerant Line Routing
15.47 (393)
18.94 (481)
65
A085862
Fig. 4 --- 9k Mounting Plate Spacing
21.93 (557)
3.15 (80)
7" (178)
10.4 (264)
If piping is going through the back:
1. Determine pipe hole position using the mounting plate as a
template. Drill pipe hole diameter per chart below. The
outside pipe hole is 1/2--in. (13 mm) min. lower than inside
pipe hole, so it slants slightly downward (see Fig. 9).
If piping is going to exit from the left rear, it is recommended to field--fabricate piping extensions to get the flare connections to the outside of the wall.
10.4 (264)
1/2 in. (13 mm)
Min.
INDOOR
65
OUTDOOR
A07371
Fig. 9 --- Drill Holes
Note: Units in ( ) = mm
Model Size
A08291
Fig. 5 --- 12k Mounting Plate Spacing
9k, 12k and 18k
24k
6
Hole Diameter
in. (mm)
2.56 (65)
3.75 (95)
If piping is going through the right or left side:
1. Use a small saw blade to carefully remove the corresponding plastic covering on side panel and drill the appropriate
size hole where the pipe is going through the wall. See Fig.
8(c).
2. Remove knockout 1 if you are running only the wiring.
Remove knockout 1 and 2 or knockout 1, 2 and 3 if you are
running both piping and wiring through the side of the unit.
INSTALL ALL POWER AND INTERCONNECTING
WIRING TO OUTDOOR UNIT
Strong
wind
OUTDOOR UNIT INSTALLATION
1. Use a rigid base to support unit in a level position.
2. Locate outdoor unit and connect piping and wiring.
CAUTION
A07350
Fig. 11 --- High Wind Installation
EQUIPMENT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
Excessive torque can break flare nut depending on
installation conditions.
Piping Connections to Outdoor Unit
IMPORTANT: Use refrigeration grade tubing ONLY. No
other type of tubing may be used. Use of other types of tubing
will void manufacturer’s warranty.
Make sure there is enough piping to cover the required length
between the outdoor and indoor unit.
Piping Guide:
S Do not open service valves or remove protective caps from
tubing ends until all the connections are made.
S Bend tubing with bending tools to avoid kinks and flat spots.
S Keep the tubing free of dirt, sand, moisture, and other
contaminants to avoid damaging the refrigerant system.
S Avoid sags in the suction line to prevent the formation of oil
traps. Insulate each tube with minimum 3/8--in. (10 mm) wall
thermal pipe insulation. Inserting the tubing into the insulation
before making the connections will save time and improve
installation quality.
1. Remove service valve cover if provided with unit.
2. Cut tubing with tubing cutter.
3. Install correct size flare nut onto tubing and make flare connection.
4. Apply a small amount of refrigerant oil to the flare connection on the tubing.
5. Properly align tubing in with service valve.
6. Tighten flare nut and finish installation using two wrenches
as shown in Fig. 10.
Outdoor Unit Wiring Connections
1. Mount outdoor power disconnect.
2. Run power wiring from main box to disconnect per NEC
and local codes. Set outdoor unit in place.
3. Remove field wiring cover (on sizes 9k, 12k, and 18k) from
unit by removing screws. On size 24k, use the knockout
provided on the end panel.
4. Connect conduit to the conduit panel on sizes 9k, 12k, and
18k. (See Fig. 12)
5. Properly connect both power supply and control lines to terminal block per the connection diagram.
6. Ground unit in accordance with NEC and local electrical
codes.
7. Use lock nuts to secure conduit.
8. Reinstall field wiring cover on 9k, 12k, and 18k units.
!
CAUTION
EQUIPMENT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
S Be sure to comply with local codes while running wire
from indoor unit to outdoor unit.
S Every wire must be connected firmly. Loose wiring may
cause terminal to overheat or result in unit malfunction.
A fire hazard may also exist. Therefore, be sure all wiring
is tightly connected.
S No wire should be allowed to touch refrigerant tubing,
compressor or any moving parts.
S Disconnecting means must be provided and shall be
located within sight and readily accessible from the air
conditioner.
S Connecting cable with conduit shall be routed through
hole in the conduit panel.
A07354
Fig. 10 --- Tighten Flare Nut
7
38/40GXC(Q)
!
Outdoor
unit
Terminal Block
G
Conduit panel
Conduit
38GXQ-40GXQ009, 012 115-1-60 Connection Diagram
CONNECTING CABLE
OUTDOOR TO INDOOR
L
N
L
N
Main
Pow er to
Pow er
Indoor
Supply
Unit
115-1-60
115-1-60
GND
S
L
N
GND
S
Ground
Control
Indoor Unit
Ground
Pow er
Control
Supply
115-1-60
38/40GXC(Q)
All 38GXQ 115-1-60 Outdoor Units
All 40GXQ 115-1-60 Indoor Units
38GXQ-40GXQ012, 018 & 024 208/230-1-60 Connection Diagram
CONNECTING CABLE
OUTDOOR TO INDOOR
L1
L2
L1
L2
GND
S
L1
L2
Main
Pow er to
Indoor Unit
Pow er
Indoor
Pow er
Ground
Control
Supply
Unit
Supply
208/230-1-60
208/230-1-60
208/230-1-60
All 38GXQ 208/230-1-60 Outdoor Units
GND
S
Ground
Control
All 40GXQ 208/230-1-60 Indoor Units
A09666
Fig. 12 --- Field Wiring
INSTALL ALL POWER, INTERCONNECTING
WIRING, AND PIPING TO INDOOR UNIT.
Field Wiring
Cover
1. Run interconnecting piping and wiring from outdoor unit to
indoor unit.
2. Pass interconnecting cable through hole in wall (outside to
inside).
3. Lift indoor unit into position and route piping and drain
through hole in wall (inside to outside). Fit interconnecting
wiring into back side of indoor unit.
4. Hang indoor unit on upper hooks of wall mounting plate (as
shown in Fig. 13)
Interconnecting
Cable
A08279
Fig. 14 --- Field Wiring Cover
A08283
Fig. 13 --- Hanging Indoor Unit
5. Open front cover of indoor unit and remove field wiring terminal block cover (see Fig. 14)
6. Pull interconnecting wire up from back of indoor unit and
position in close to the terminal block on indoor unit.
7. Push bottom of indoor unit onto mounting plate to complete wall mount.
8. Connect wiring from outdoor unit per connection diagram
(see Fig. 12).
NOTE:
Polarity of power wires must match original
connection on outdoor unit.
9. Replace field wiring cover and close front cover of indoor
unit.
10. Connect refrigerant piping and drain line outside of indoor
unit. Refer to Fig. 10 for proper installation of flare connections. Complete pipe insulation at flare connection then
fasten piping and wiring to the wall as required. Completely seal the hole in the wall.
8
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
Deep Vacuum Method
The deep vacuum method requires a vacuum pump capable of
pulling a vacuum of 500 microns and a vacuum gage capable of
accurately measuring this vacuum depth. The deep vacuum method
is the most positive way of assuring a system is free of air and
liquid water. (See Fig. 17)
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
Never use the system compressor as a vacuum pump.
SYSTEM VACUUM AND CHARGE
Using Vacuum Pump
1. Completely tighten flare nuts A, B, C, D, connect manifold
gage charge hose to a charge port of the low side service
valve. (See Fig. 15.)
2. Connect charge hose to vacuum pump.
3. Fully open the low side of manifold gage. (See Fig. 16)
4. Start vacuum pump
5. Evacuate using either deep vacuum or triple evacuation
method.
6. After evacuation is complete, fully close the low side of
manifold gage and stop operation of vacuum pump.
7. The factory charge contained in the outdoor unit is good for
up to 25 ft. (8 m) of line length. For refrigerant lines longer
than 25 ft (8 m), add 0.1 oz. per foot of extra piping up to
the maximum allowable length.
8. Disconnect charge hose from charge connection of the low
side service valve.
9. Fully open service valves B and A.
10. Securely tighten caps of service valves.
Indoor Unit
Refrigerant
Outdoor Unit
A
Low Side
B
High Side
C
D
LEAK IN
SYSTEM
MICRONS
Refrigerant tubes and indoor coil should be evacuated using the
recommended deep vacuum method of 500 microns. The alternate
triple evacuation method may be used if the procedure outlined
below is followed. Always break a vacuum with dry nitrogen.
VACUUM TIGHT
TOO WET
TIGHT
DRY SYSTEM
0
1
2
3 4
5
MINUTES
6
7
A95424
Fig. 17 --- Deep Vacuum Graph
Triple Evacuation Method
The triple evacuation method should only be used when vacuum
pump is only capable of pumping down to 28 in. of mercury
vacuum and system does not contain any liquid water.
Refer to Fig. 18 and proceed as follows:
1. Pump system down to 28 in. of mercury and allow pump to
continue operating for an additional 15 minutes.
2. Close service valves and shut off vacuum pump.
3. Connect a nitrogen cylinder and regulator to system and
open until system pressure is 2 psig.
4. Close service valve and allow system to stand for 1 hr. During this time, dry nitrogen will be able to diffuse throughout
the system absorbing moisture.
5. Repeat this procedure as indicated in Fig. 18. System will
then be free of any contaminants and water vapor.
EVACUATE
Service Valve
A07360
BREAK VACUUM WITH DRY NITROGEN
Fig. 15 --- Service Valve
WAIT
Manifold Gage
EVACUATE
BREAK VACUUM WITH DRY NITROGEN
500 microns
Low side valve
Charge hose
WAIT
High side valve
EVACUATE
Charge hose
CHECK FOR TIGHT, DRY SYSTEM
(IF IT HOLDS DEEP VACUUM)
Vacuum pump
RELEASE CHARGE INTO SYSTEM
Low side valve
A95425
Fig. 18 --- Triple Evacuation Method
A07361
Fig. 16 --- Manifold
Final Tubing Check
IMPORTANT: Check to be certain factory tubing on both indoor
and outdoor unit has not shifted during shipment. Ensure tubes are
not rubbing against each other or any sheet metal. Pay close
attention to feeder tubes, making sure wire ties on feeder tubes are
secure and tight.
9
38/40GXC(Q)
CAUTION
!
START--UP
Test Operation
Perform test operation after completing gas leak and electrical
safety check.
1. Push the “ON/OFF” button on Remote Control to begin
testing.
NOTE: A protection feature prevents the air conditioner from
being activated for approximately 3 minutes.
2. Push MODE button, select COOLING, HEATING, FAN
mode to check if all functions work correctly.
38/40GXC(Q)
SYSTEM CHECKS
1. Conceal the tubing where possible.
2. Make sure that the drain tube slopes downward along its entire length.
3. Ensure all tubing and connections are properly insulated.
4. Fasten tubes to the outside wall, when possible.
5. Seal the hole through which the cables and tubing pass.
Explain Following Items To Customer With The Aid Of The
Owner’s Manual:
1. How to turn air conditioner on and off; selecting
COOLING, HEATING and other operating modes; setting
a desired temperature; setting the timer to automatically start
and stop air conditioner operation; and all other features of
the Remote Control and display panel.
2. How to remove and clean the air filter.
3. How to set air deflection louver.
4. Explain care and maintenance.
5. Present the Owner’s Manual and installation instructions to
customer.
INDOOR UNIT
1.
2.
3.
4.
Do all Remote Control buttons function properly?
Do the display panel lights work properly?
Does the air deflection louver function properly?
Does the drain work?
OUTDOOR UNIT
1. Are there unusual noises or vibrations during operation?
10
TROUBLESHOOTING
This unit has onboard diagnostics. Error codes will appear on the LED display on the front panel of the indoor unit in place of the
temperature display. Error codes are also displayed on the outdoor unit microprocessor board with colored LED lights. The table below
explains the error codes for both units.
38GXC/GXQ -- 40GXC/GXQ 009--024 Diagnostic Codes
LED Display on Outdoor Unit Board
Green
LED
Number
of Flashes
Red
LED
Number
of Flashes
Yellow
LED
Number
of Flashes
4
3
Low Refrigerant Charge, Blocked Indoor Air
Flow, or Dirty Air Filter
7
Low Refrigerant Charge, Blocked Capillary,
or High Ambient Temperature
5
Low Voltage
Possible Cause
Freeze Protection, Indoor Coil
E2
High Compressor Discharge Temperature
E4
Low Voltage Protection
E5
Communication Error
E6
Indoor Air Temperature Thermistor
F1
Indoor Coil Temperature Thermistor
F2
Outdoor Air Temperature Thermistor
F3
6
Bad Connection, or Sensor Failure
Outdoor Coil Temperature Thermistor
F4
5
Bad Connection, or Sensor Failure
Compressor Discharge Line Thermistor
F5
7
Defrost
H1
2
Unit going through normal defrost cycle
Compressor Overload Protection
H3
8
Low Refrigerant Charge, Blocked Capillary,
or Compressor Motor Failure
Compressor Over Current Protection
H4
6
High Ambient Temperature, or Loss of
Condenser Airflow
IPM Module Protection
H5
4
Loss of Cooling to Heat Sink, High Ambient,
Low Voltage, or Bad Connections
0
Wiring Error, or Communication Failure
Bad Connection, or Sensor Failure
Bad Connection, or Sensor Failure
11
Bad Connection, or Sensor Failure
38/40GXC(Q)
Equipment Fault
Code Displayed
on Indoor Unit
Front Panel
38/40GXC(Q)
Copyright 2011 Carrier Corp. S 7310 W. Morris St. S Indianapolis, IN 46231
Printed in U.S.A.
Edition Date: 04/11
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
12
Catalog No: 38---40GX ---5SI
Replaces: 38--- 40GX--- 4SI
Download PDF