Lennox CHA16-024, Руководство по обслуживанию

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11-Defrost Control CMC1
The CMC1 defrost control (figure 5 ) is a solid state control
which provides automatic switching from normal heating operaĆ
tion to defrost mode and back. The control provides maximum
14 minute defrost periods at 30, 60 or 90Ćminute fieldĆchangeĆ
able intervals. Each control monitors thermostat demand and
holds" the timer in place between thermostat demand. A set of
diagnostic pins are also provided for troubleshooting the refrigĆ
eration circuit.
The control contains a solid state timer which switches an exĆ
ternal defrost relay through 1/4" male spades mounted on the
control's circuit board. The control energizes the defrost relay
at regular timed intervals. Defrost thermostat S6 initiates deĆ
frost and pressure switch S46 terminates defrost. If S46 does
not terminate defrost, CMC1 will terminate defrost after 14
minutes.
SOLID STATE DEFROST TIMER
TIMING JUMPER
TIMING PINS
TROUBLESHOOTING
PINS
CONTROL
TERMINALS
FIGURE 5
When the indoor thermostat closes (call for heat or cool), deĆ
frost timer initiates 30, 60 or 90Ćminute (depending on how the
control is preset) timing sequence. At the end of the timing seĆ
quence, the control attempts to energize the defrost relay. If
both defrost thermostat and defrost pressure switch are
closed when timing sequence ends, the defrost relay is enerĆ
gized and defrost begins. Consequently, the defrost pressure
switch must open in order for defrost to be terminated (defrost
can also be terminated by the internal timer of the defrost conĆ
trol).
Defrost Control Components
a- Timing Pins 30(T1), 60(T2), 90(T3)
Each of these pins provides different timed interval beĆ
tween defrosts. A jumper connects the pins to circuit
board pin W1. Table 1 shows the timings of each pin.
The defrost interval can be field changed to 30, 60 or 90
minutes. The defrost period (14 minutes) cannot be
changed. To change the interval between defrosts, simĆ
ply remove the jumper from the pin it is connected to and
reconnect the jumper to one of the other available pins
(see figure 6).
NEEDLE-NOSE
PLIERS
TO CHANGE CONTROL TIMINGS:
1- Turn off all power to the unit to avoid damaging the circuit board.
2- Grasp wire connector firmly with needle nose pliers as shown.
3- Gently pull connector from pin.
4- Select new timing pin. DO NOT SELECT A TST" PIN.
5- Gently push connector onto desired pin (see Table 1 for timings).
Connector is seated when pin snaps.
6- Turn on power to unit.
IMPORTANT
Prevent control damage. Do not connect timing
jumper to either TST" pin.
Prevent control damage. Avoid contact with other
control terminals or control components.
IMPORTANT
FIGURE 6
b- Timing Jumper
A timing jumper is factory installed on the circuit board
and is used to connect pin W1 to one of three timing
pins. The jumper may be connected to any one timing
pin but must never be connected to the TST" pins. See
following Caution.
IMPORTANT
Potential for control damage.
Do not connect timing jumper to TST" pins.
TST" pins are used only during a test and must
not connect with timing pins.
TABLE 1
DEFROST
CONTROL CMC
TIMINGS
INTERVAL BETWEEN
JUMPER CONNECTED TO:
DEFROST
TIME
30 (T1) 60 (T2) 90 (T3)
NORMAL
OPERATION
TST" PINS
JUMPERED
30 + 3 60 + 6 90 + 9 14 + 1.4
7 + 0.7 14 + 1.4 21 + 2.1 3.3 + 0.3
MIN. MIN. MIN. MIN.
SEC. SEC. SEC. SEC.
TOGETHER
DEFROSTS WITH
c- 24V" Terminal
Terminal 24V" receives 24VAC from the control transĆ
former. This terminal powers the control's internal timer
and relays. Terminal 24V" must be powered at all times
in order to provide HOLD" between thermostat deĆ
mands.