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5.7B Programmable Ventilation Timer
The ventilation timer controls the fan and the motorized
fresh air damper. When the ventilation timer is
activated, the central conditioning unit will circulate the
indoor air, and bring in fresh air from outside. The
ventilation timer should be set for the required
ventilation of the residence. The home should be
ventilated with fresh air as suggested by applicable
codes and standards.
If the DHV-150H fails to ventilate as expected, check
that the time on the timer is correct. For the timer to
carry out the program schedule, the slide switch in the
upper left corner on the timer must be set to “AUTO”.
The slide switch in the upper right corner of the DHV-
150H must be set to “RUN”. Also check the programs on
the timer to be sure that the timer is calling for
ventilation at the correct times. If the timer fails to
operate or operates erratically, reset the timer; see
section 3.5 of this manual.
5.8 Defrost Thermostat
The defrost thermostat is attached to the refrigerant
suction tube between the accumulator and the
compressor. It will automatically shut the compressor off
if the low side refrigerant temperature drops due to
excessive frost formation on the evaporator coil. The
fan will continue to run, causing air to flow through the
evaporator coil and melt the ice. When the ice has
melted, the evaporator temperature will rise and the
thermostat will restart the compressor.
5.9 Electric Ventilation Damper
The ventilation timer controls the electric ventilation
damper. The damper will open when the ventilation
timer is activated to allow fresh air into the structure
through the 6” diameter fresh air inlet duct. The electric
ventilation damper will remain closed when the
ventilation timer is not activated to prevent over-
ventilating the structure when the unit is dehumidifying
or recirculating the indoor air.
The electric ventilation timer operates on 24 Vac from
the control circuit. DO NOT connect high voltage to the
damper motor or damage to the motor may result. DO
NOT force the blade of the damper by hand or damage
to the damper motor may result.
If the electric ventilation damper fails to operate:
1. Check that the wiring is correct and that voltage is
present at the damper motor.
2. Check for any obstruction inside the damper.
If the electric ventilation damper fails to operate after
performing these checks, it must be replaced.
If the low side refrigerant pressure drops to 15 PSIG, the
low-pressure control opens and shuts off the compressor
and fan. It is an automatically reset control. It will close
when the refrigerant pressure rises to 35 PSIG. Its
primary function is to prevent damage to the
compressor if a leak develops in the refrigeration
system. It may also open if the unit is A) installed in a
cool area (below 50 F) or B) installed where it is below
40 F and then started. Under these conditions, the unit
will restart within several minutes. Until the unit warms
up, it may cycle several times.
An optional condensate pump kit is available from the
factory for use with the DHV-150H. Condensate is
automatically pumped to a remote location when the
water level in the pump's reservoir rises to close the
float switch.
The pump also contains a safety float switch. The
white leads from this switch extend from beneath the
pump cover. This switch should be installed in series
with the field wire that connects the blue (#5) lead from
the DHV-150H to the blue (#5) lead on the control
panel.
If the pump fails, this switch opens the compressor
control circuit and stops water production before the
reservoir overflows. The DHV-150H will continue to
ventilate or circulate air as normal, but will not
dehumidify until this switch closes.