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When the external temperature is below 34ºF, the compressor clutch and condenser will be
locked out to prevent condenser motor damages. If the external temperature sensor is
damaged, it may feed false low temperature signal to the board and cause the system
malfunction.
Fan Speed Control
EC3.0 system has two speed control modes. Auto fan speed control and manual fan speed
control. In manual fan speed control, there are three settings High, Medium and Low. In
auto fan speed control mode, evaporator blower speed is controlled based on the temperature
differential between Tin and Tset. The greater the temperature differential is the higher the
blower speed is. The evaporator blower is controlled by a series of transistors instead of
relays. By changing the duty ratio of the transistors, the supply voltage to the blower can be
varied. As the blower speed is proportional to the input voltage, the blower speed can be
controlled by duty ratio. The fan speed control setting are listed in Table 6.
Table 6 Fan speed control settings
Mode
Setting
| Tin-Tset | ≤ 2ºF
Auto
2Fº<| Tin-Tset | < 4ºF
4Fº≤| Tin-Tset | < 6ºF
6Fº≤| Tin-Tset | < 8ºF
8Fº≤| Tin-Tset |
Manual
High
Mediu,
Low
Tie-In Configuration
The EC3.0 system has three designated terminals (terminal 2,4 and 7) to control an additional
tie-in system. Terminal 4 senses the tie-in signal (+12 vdc). Terminal 2 and 7 control tie-in
compressor and tie-in condenser respectively. The status of the tie-in system does not affect
the operation of the stand along system.
Table 7 Tie-In Configurations
System
Tie-in terminal
EC3.0 ON
Open
(dash off)
+12 VDC
EC3.0 ON
(dash on)
+12 VDC
EC3.0 OFF
(dash on)
Safety and Fault Protections
There are two or three safety switches in a EC3 system. High pressure switch, low pressure
switch and freezestat (if equipped). Safety switches are wired in parallel to the safety
harness. There are 4 wires in the safety harness: one common wire, and 3 switch wires.
Refer to installation drawing for detailed wiring diagram. The common wire carries +5 vdc
and it is connected to all the safety switches through a comment joint. If a safety is closed
Duty Ratio
60%
70%
80%
90%
100%
100%
80%
60%
Clutch & Condenser relays
Tie-in condenser and tie-in compressor remain OFF.
Rest of system controlled by EC3.0 board
All system components controlled by EC3.0 board
Tie-in condenser and tie-in compressor ON
Rest of system OFF
EC3 Service Manual Jan. 8, 2008
4
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