Unit Options; Proof Of Airflow Switch; Frost Protection Switches; Clogged Filter Switch - McQuay SWP Series Installation And Maintenance Manual

Unit Options

Proof of Airflow Switch

Unit Options
A positive proof of airflow switch (PC7) is provided with all
units. The switch is factory set to close at 0.2 inches H
switch has a field-adjustable set point range of 0.05 to 5.0
inches H 0. Turn the adjustment screw clockwise to decrease
2
differential pressure setting. Turn the adjustment screw
counterclockwise to increase differential pressure setting.
In a constant volume system, if the fan system is energized and
the minimum pressure setting of the switch has not been
reached, the unit shuts down and a loss of airflow alarm is
indicated at the MicroTech III controller. For variable air
volume units, the unit shuts down due to loss of airflow only if
the airflow switch is open AND the duct static pressure is less
than half the duct static pressure set point. Once the reason for
the fault is corrected, manually reset the unit through the
MicroTech III keypad/display interface. PC7 is located in the
fan section on the motor side.

Frost Protection Switches

A frost protection switch (FP1-FP6) is used on each refrigerant
circuit to protect against evaporator coil freeze up. These
switches normally are closed and open on a drop in
temperature. When a frosting condition is sensed, the
compressor circuit shuts down until the condition is removed.
The frost protection control is an automatic reset control. If the
condition occurs on any one compressor three times in a 24
hour period, the alarm has to be manually reset through the
MicroTech III keypad/display interface to restart the
compressor. The MicroTech III control indicates a warning
when a frost condition exists. The temperature sensors are
located on a DX return bend for each refrigerant circuit.

Clogged Filter Switch

A clogged filter switch (PC5) is provided to indicate when the
unit filters are to be changed. The switch is factory set to close
at 1.0 inches of H O. The switch has a field-adjustable set
2
point range of 0.05 to 5.0 inches of H
screw clockwise to decrease differential pressure setting. Turn
the adjustment screw counterclockwise to increase differential
pressure setting. When the filter pressure differential exceeds
the switch setpoint, MicroTech III controller displays a
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0. The
2
O. Turn the adjustment
2
clogged filter indication. The unit is allowed to continue
operation. PC5 is located in the fan section on the motor side.

Winterizing Water Coils

Coil freeze-up can be caused by such things as air stratification
and failure of outdoor dampers and/or preheat coils. Do not
depend on routine draining of water cooling coils for winter
shutdown or to protect against freeze-up. Severe coil damage
can result. Drain all coils as thoroughly as possible and then
treat each of them in the following manner:
• Fill each coil independently with an antifreeze solution
using a small circulating pump and thoroughly drain again.
• Check the freezing point of the antifreeze before proceeding
to the next coil. Due to a small amount of water always
remaining in each coil, there is a diluting effect. The small
amount of antifreeze solution remaining in the coil must
always be concentrated enough to prevent freeze-up.
Carefully read instructions for mixing antifreeze solution.
Some products have a higher freezing point in their natural
state than when mixed with water.

Duct High Limit

A duct high limit (DHL) pressure control is provided as
standard with all units with variable air volume control. The
duct high limit is intended to protect the ductwork, etc. from
over pressurization caused by tripped fire dampers or a control
failure. When the duct pressure exceeds the setting of the
control, the unit de-energizes via the MicroTech III controller,
which displays an alarm condition. After the reason for trip is
identified and corrected, reset the control via the MicroTech III
keypad/display interface.
The duct high limit control is factory installed, including
sensing tubing, and preset for a 3.0" inches of H
The control can be readjusted in the field to match the specific
ductwork of a project. The switch has a field-adjustable set
point range of 0.05 to 5.0 inches of H
screw clockwise to decrease differential pressure setting. Turn
the adjustment screw counterclockwise to increase differential
pressure setting. The DHL is located in the fan section on the
motor side.
O trip point.
2
O. Turn the adjustment
2
McQuay IM 937