Transcript No Slide Title

Heat Pump Defrost Controls
Follows Pub No. 34-4101-07
Theory of Operation
page 3
• DFCs use a temperature sensing switch and
a electronic timer circuits with on board
relays to control the outdoor fan, switch
over valve, heat strips and EDR
• The DT is usually attached to the lowest
circuits of the outdoor coil
• The DT contact close at 40 degrees or
below (Temp is not standard for all models
check service facts)
Theory of Operation
page 3
• Compressor run time is accrued and
memorized by DFC as long as “Y” call
(24V AC applied between DFC Y & B
Terminals) is made from indoor thermostat.
When the DT switch contacts are open and
the call for Y is removed the timers is reset
to Zero and restarted on the next call on Y
Theory of Operation
page 3
• When the DT switch contacts are closed and
the indoor thermostat terminate the call for
Y. The timing is memorized and will resume
on the next Y call.
• The DFT Timer is activated when 24 VAC
is applied to DFT R&B terminals.
• The Test pins should not be jumped unless
attempt is being made to speed up timer.
Theory of Operation
page 3
• A defrost cycle is initiated when the DT
switch contacts close and the compressor
run time has accrued the preset run time.
• When Defrost is initiated, the DFC stops the
out door fan, energizes the auxiliary heat
and reverses the refrigerant cycle to the
cooling mode by energizing the SOV.
Theory of Operation
page 3
• The Defrost cycle is terminated when the
DT switch opens (50 to 70 degree outdoor
coil temp.) or the 10 minute timer overrides
has elapsed.
• TST pins are shorted the timing is divided
by 256 (90 minutes = 20 seconds)
CNT1642
Service Checks
page 4
• Short R to D
• Momentary Short
TST
• Remove short
when outdoor fan
stops
24V
Service Checks
24V
Service Checks
24V
Service Checks
Control Checkout
Page 5
Timer Defrost Control
Supersedure
Page5
Adaptability
• The latest control models control models
are applicable to many different heat pump
products with up to 14 SEER ratings and
minimize ID/OD mismatch and various
electrical installation problems.
Logic Process
• Microcomputer logic is used to monitor
• Uses two remote sensors
• Learning process
Defrost On Demand
• Controls permit defrost only when coil icing
conditions begin to cause serious heat pump
capacity reductions.
Diagnostics
• Detected faults displayed by flashing Light
Emitting Diode (LED) on circuit board.
• Board provides output signal that can flash
emer. heat light on the indoor thermostat
• Fault circuit not found on newest boards
Time Override
• The Control prevents the system from being
locked into the defrost cycle by automatic
time termination.
Soft Switch-over
• The outdoor fan comes back on 12 seconds
before switch over valve coil is deenergized
• This allows the Head pressure in system to
be reduced
• Lower Refrigerant Velocity
• Prevents liquid hammer
Theory of Operation
Page 10
• Uses Two Thermistor
sensors
Theory of Operation
Page 10
• ODS-B
• Located just below the
control box
• with fan running
senses ambient air
temperature
Theory of Operation
Page 10
• The DFC is power by the system 24V
power
• DFC is activated when 24V is applied
between DFC R and B and the test lead is
on the “NORM” pin
• LED will flash once per second
Theory of Operation
Page 10
• First power up with the outdoor
temperature below 52 F and the coil sensor
temperature is below 36 F and the control
has counted 30 minutes of run time the
DFC will initiate Defrost (2 min. run time)
• DFC records clean coil Delta T
• Next defrost will be on demand
Theory of Operation
Page 10
• Defrost cycle is initiated when the current
T exceeds the T initiate = current T X
2.0 + temperature bin correction factor
• The initiate T is not a constant value, but
is a value that the DFC calculated for a
complete defrost cycle at that specified out
door temperature.
Theory of Operation
Page 10
• Ambient air sensor is turned off while DFC
is in the defrost mode.
• Defrost termination as soon as one minute
• Memorized pre-defrost cycle ODT
conditions are used to determine coil T
terminate values.
Test Modes
Page 11
• TEST MODE
• To speed up defrost
cycles times
• Move Red jumper
from NORM to TST
• LED rapid flash
Test Modes
Page 11
• FORCED DEFROST
• Use instead of TST
• Doesn’t Require
sensors to enable
Test Modes
Page 11
• FORCED FAULT
• Not applicable to defeatured boards
• move red jumper from
normal to FRC FLT
• reset by moving emerswitch on thermostat
on and then off
Page 12
Page 12
Fault Detection
page 13
• FAULT A
•
•
•
•
•
•
2 quick Flashes per second
Low delta-T or low Heat Pump capacity
Inoperative compressor
Shorted coil sensor
Open ambient sensor
Flashes LED after three times Defrost terminates
with Low delta T
Fault Detection
page 13
• FAULT B
• 3 quick flashes per second
• Defrost terminates on maximum override time of
15 minutes instead of temperature
• DFC will become timer defrost control after 10
consecutive terminations on maximum override
• Every 30 minutes (not reported to thermostat)
Fault Detection
page 13
• FAULT C
•
•
•
•
•
•
•
•
3 quick flashes per second
Vary high delta-T
SOV stuck in heat mode
Inoperative solenoid
outdoor fan failure
open coil sensor
shorted ambient air sensor
Will reset if system returns to normal
Fault Detection
page 13
• FAULT A and B or A and C
•
•
•
•
•
4 quick flashes per second
60 or more A faults and 1 or more B faults
60 or more A faults and 1 or more C faults
Will flash fault light
Will reset if system returns to normal
Page 14
Page 15
Sensor Check
Page 16
• Measure the
Temperature the
sensor is exposed to.
• When the coil sensor
temp. is measured.
You must measure
tubing temperature
that the sensor is
measuring.
Sensor Check
Page 16
K
• Unplug the sensor
from the DFC
• Measure the resistance
with a good quality
Ohmmeter
• Read the value as
quickly as possible
• This will prevent
meter current from
changing value
Values Correct In Book
Sensor Check
Page 16
• Using the chart on
page 16
• Locate the closely as
possible the actual
sensor temperature
• We measured a ohm
value of 12.3K and a
sensor temperature of
70 F
12.3K = 68.7
Service Checks
• Must have 24V - 30V
to R and B or control
is brain dead
Service Checks
• Must have 24V to 30V
to Y and B also to
initiate Defrost.
Service Checks
• Insure that the sensor
are OK
• Measure Voltages at Y
and B and R and B
• Common and N.C on
fan relay
Page 17
Page 18
ECM Control
Fan Motor
Page 19
New Generation De-featured
Controls
Page 20
• Used with Reciprocating and Scroll
Compressor Units
• Last Quarter of 1998 eight New boards
• Check Service Literature for suitable
replacement
• DFC for Scroll compressor time delay
• MS control coil is powered by YO from
DFT
TM
• Lite Port
“LITE PORT”
• Emerging Technology
• Will utilize Optical Coupler and Computer
• Code from LED will be interpreted to
gather more details of operation
• You will see more on this in the future
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Page 6
Heat Pump Electrical
Components and Circuits
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