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9 Detailed Sequence of Events
– Control Operation
1) Turning on Main Disconnect at dehumidifier provides
480 VAC, 3 phase power to the control panel. Power is
distributed to breakers for blower motors, heaters and
the control transformer. The control transformer
supplies 115 VAC for control system and desiccant
wheel motor.
a) PHASE OUT lamp, if illuminated, indicates the
power supply is not connected correctly. Rewire
power supply as needed.
b) STANDBY lamp illuminates.
c) Rotor motor terminals, 3470 and X2, energize
providing the desiccant motor with 115 VAC power.
Desiccant wheel begins to rotate.
d) Reactivation motor starter RMS contacts close,
starting the reactivation blower.
e) COOL DOWN light illuminates, indicating the timed
heater cool down cycle has started.
f) Time relay TR1 starts the 5 minute heater cool
down cycle. Contacts are normally closed, timed
open (NCTO). Following the delay…
I) TR1 relay energizes, opening contacts for the
COOL DOWN light and reactivation blower
motor starter (RMS). Rotor motor terminals
3470 and X2 de-energize.
Note: The cool down cycle can be interrupted if the RUN
position is selected and no alarm conditions are present.
2) Selecting the RUN position (selector switch) …
a) Provides power to the temperature control TC.
b) Start relay SR energizes, if no alarm conditions
are present (AR relay de-energized)
I) Time relay TR1 and COOL DOWN light
de-energize. Run indicator illuminates.
Reactivation blower motor starter is energized.
Pressure switch PS1 is activated when
reactivation airflow reaches minimum level.
II) TDR2 starts a 20 second delay followed
by energizing Process motor start (PMS), hour
meter, and TDR4 40sec timer. If pressure
switch PS1 was not activated in previous step
due to lack of airflow, Alarm relay is energized
and unit is not allowed to run.
III) Heater “A” Relay HAR energizes, if auxiliary
contacts of the reactivation motor overload
(RMS) are closed and the temperature control
is calling for heat.
IV) Upon TDR4 reaching 40seconds, remaining
heat contactors HBR and HCR are energized
3) If temperature in reactivation heater plenum exceeds
375°F, the temperature control TC will close its
auxiliary contact, energizing the latching alarm
relay AR.
a) ALARM lamp illuminates.
b) Alarm horn sounds.
c) Terminals 3080 and X2 energize. These
terminals can be utilized for an external alarm
(1 amp maximum).
d) Time relay TR1 starts the 5 minute heater cool
down cycle. Following the delay…
I) TR1 relay energizes, opening contacts for the
COOL DOWN light and reactivation blower
motor starter (RMS). Rotor motor terminals
3470 and X2 de-energize.
Reset alarm by turning the selector switch to
STANDBY.
Probable causes for a high temperature fault are
reduced air flow, dirty filter, incorrect reactivation
blower rotation, or blower failure.
4) On a fault from an overload relay (OLR-P or OLR-R), the
latching alarm relay (AR) energizes. The effect is listed
in lines 3a through 3d.
Turn the selector switch to STANDBY, allowing the
cool down cycle to complete before turning OFF the
main disconnect. Follow Lock Out – Tag Out procedure
to de-energize the power cord supplying the 4800.
Reset the overload relay located in the control
cabinet. Close and secure cabinet door. Energize unit
following proper Lock Out – Tag Out procedure.
Probable causes for a fault from an overload relay
are insufficient restriction of airflow (overloading motor
by allowing excessive airflow) or blower/motor failure.
5) On a fault from the internal process dehumidistat
that persists for 20 minutes, the latching alarm relay
(AR) energizes. The effect is listed in lines 3a through
3d. TDR1 provides a 10 minute delay for the removal
of residual humidity desiccant during startup.
Reset alarm by turning the selector switch to
STANDBY.
Probable causes for a fault from the internal
dehumidistat are heater failure or desiccant failure.
6) On a fault from a stuck heater contactor, the Alarm Relay
will energize and the reactivation blower will remain on
continuously. The Rotor will continue to turn, but the
process blower will NOT come on. Shut off power with the
main disconnect and replace the inoperable contactor to
clear the error.
No dehumidistat is provided to monitor process inlet air
condition (see over-dry warning section 3.5). An external
control (dehumidistat, thermostat or other dry contact)
can be wired in place of the jumper across terminals
1 and 3082. The external control must be designed to
operate a 115 VAC circuit. Contact closure will start
dehumidification. A control wired across terminals 1 and
3082 will be in series with the selector switch. Turn the
selector switch to RUN to operate the dehumidifier from
an external control.
