5
DDT40 Adaptive Defrost Control
Recommended Thermistor Probe Position
The probe should be positioned and fastened wherever
frost accumulates most quickly. This is generally 1" to 2"
(2.5 cm to 5 cm) from either end, at the bottom quarter
and at the discharge side of the evaporator coil. If there
is uncertainty about where frost typically accumulates
the fastest, put the system into a manual defrost (see
"Optional: Manual Defrost" on page 10) and monitor
the last area of the evaporator where frost is present
prior to a completely frost-free coil.
Make sure the probe is not fastened in close proximity
to the electric defrost heating element.
7. Route the thermistor probe wires away from the
evaporator fans and cooling fins, avoiding pinches
and strain. Route the wire through existing or new line
voltage conduits. Secure the wires as appropriate for
your installation.
8. Use the provided wire connectors to connect the
thermistor probe wire to the routed 18–14 AWG field-
supplied wire.
9. Use electrical tape to protect all connections against
moisture.
10. If additional thermistor probes are needed repeat all
steps in this section. For large evaporators, you can
add a thermistor probe to a coil on each (opposite) side.
11. For multiple-evaporator installations, see "Optional:
Multiple Evaporators" on page 10.
Evaporator Coil
Clip
FIG. 10
Connect Thermistor Probe to Evaporator Coil
Mode Selection
Determine which defrost control (Grässlin™ or other manufacturer) will be replaced as indicated in TABLE 1. The mode
selector DIP switch (located at the lower right side of the board) determines the configuration of terminals 2 and 4. In position
“A”, the terminals are normally closed, and will open during a defrost. In position “B”, terminals 2 and 4 are normally open,
and will close during a defrost. Select the proper position from the table and wiring diagrams indicated. To select mode simply
slide the switch as follows:
• Mode A - position switch up;
• Mode B - position switch down;
In most applications, the contacts at terminals 2 and 4 are
normally closed with S1 in the “A” position and control the
fans and refrigeration equipment or compressor. For hot gas
defrost, or for double-pole switching, contacts 2 and 4 may
be configured as normally open by selecting mode “B”. Refer
to wiring diagrams 1 through 10 for additional details.
Note:
When Mode “B” is selected the DDT40 will operate as follows:
–
Refrigeration Mode - Red and Green LEDs will turn OFF (terminals 1 and 3, 2 and 4 will be open while terminals 1
and F will be closed).
–
Defrost Mode - Red and green LEDs will turn ON (1 and 3, 2 and 4 will be closed while 1 and F will be open).
