PennBarry D11 Installation Manual

INSTALLATION INSTRUCTIONS

STAND ALONE ERV

DXX-2ERV

D-SE RIES

ENERGY RECOVERY VENTILATOR SERIES D11, D20, D28, D36, D46, D62, D80 & D12

INSTALLATION INSTRUCTIONS FOR ENERGY RECOVERY VENTILATOR (FIXED)

FOR STAND ALONE ROOFTOP APPLICATION

Energy recovery COMPONENT certified
to the AHRI Air-to-Air Energy Recovery
Ventilation Equipment Certification
Program in accordance with AHRI
Standard 1060-2000. Actual performance
in packaged equipment may vary.

ETL Certified per UL 1995
and CSA 22.2

OCTOBER 6, 2015

SUPERCEDES 10-29-14

I - Ship ping and Pack ing List

Package contains:

1 — Energy Recovery Ventilator Assembly
1 — Assembled Exhaust Hood

II - Shipping Damage

Check the unit for shipping damage. Receiving party
should contact last carrier immediately if shipping damage
is found.

III - General

These instructions are intended as a general guide and do
not supersede local codes in any way. Authorities having
jurisdiction should be consulted before installation.

IV - Requirements

When installed, the unit must be electrically wired and
grounded in accordance with local codes or, in absence of
local codes, with the current National Electric Code,
ANSI/NFPA No. 70.

V - Application

These Energy Recovery Ventilators (ERVs) are used in a
down discharge manner equipped with a field provided
balancing damper assembly through the roof. A roof
curb must be provided by contractor to manufacturers
specifications. These ventilators conserve energy by
transferring humidity and heat energy across two opposing
air streams using a rotary heat exchanger (the energy
recovery wheel). This process works in the summer by
rejecting heat energy from incoming intake air and in the
winter by conserving heat energy from the exhaust air,
allowing outdoor ventilation rates to be increased by
factors of three or more without additional energy penalty
or increase in size of heating or air conditioning systems.

VI - Rigging for lifting

1. Maximum weight of the unit varies per series
(300-1200 lbs crated)

2. Remove crating

3. All panels must be in place for rigging.

4. Remove box containing screws and accessories from
the Controls section.

5. Duct work should be installed into roof curb before
installing ERV on curb.

6. Roof curb gasket should be applied to all top surfaces
of the curb. (refer to roof curb install instructions).

7. Forklift channels (if used) must be removed from the
base of the ERV before setting unit on curb. See

Figure 1.

8. Attach lifting straps to the provided lifting lugs on the
top 4 corners of the D-11 through D-62 units, on D-80
and D-120 units cutouts are provided on the bottom 4
corners for attachment of lifting straps.

9. Position unit on roof curb being sure to provide service
access to ERV control access door and wheel.

WARNING

Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.

CAUTION

Danger of sharp metallic edges. Can cause injury.
Take care when servicing unit to avoid accidental
contact with sharp edges.

FIGURE 1

FORKLIFT CHANNELS

PAGE 1

VII - Installation

1. Install exhaust hood assembly shipped with ERV on
pallet using screws provided in accessory box. On
units with motorized exhaust damper connect Plug
(P.161) to jack after removing PK-3 jumper before
attaching hood with screws. See Figure 2.

FIGURE 2

2. Remove ERV control access panels to connect field
wiring.

Low Voltage

3. Route Class II low voltage wire (3 conductor) from
thermostat, relay, or Energy Management through
small bushing provided in the end panel in the ERV.
See Figure 3 for location of penetration.

THERMOSTAT PENETRATION

HIGH VOLTAGE KNOCKOUT

FIGURE 3

5. On units with Variable Frequency Drives a separate
terminal strip is provided to connect low voltage (0-10
VDC) controls [field supplied] for the Drives.

High Voltage

6. All Electrical connections must conform to any local
codes and current National Electric Codes (NEC) or
Canadian Electric Codes (CEC). Refer closely to unit
wiring diagram in the unit and/or in these instructions
for proper wiring connections.

7. Refer to unit nameplate for minimum circuit ampacity
(MCA) and maximum overcurrent protection size
(fuse).

8. Electrical data is listed on unit rating plate as well as
the motor name plates.

9. Connect line voltage power from field installed power
disconnect to ERV fuse block in the control box of the
unit. Use provided knockout on outside panel next to
controls section. See Wiring Diagram pg???

10. Ground unit with suitable ground connection
either through unit supply wiring or to an earth ground.

Note: Unit voltage entries must be sealed weather

tight after wiring is complete.

11. Remove motor access panels, check that blowers
have belts in place and that motors spin freely. Blower
RPM can be adjusted to meet CFM and external static
pressure requirements by adjusting the sheave on the
blower motors and by replacing the pulley kits on units
ordered without variable frequency drives. Multiple
pulley arrangements are available from the
manufacturer to meet the entire range of the units CFM
options.

Caution: Blower speed must be adjusted for the given

external static pressure and airflow (CFM)
requirements. If blower speed is not adjusted for
conditions, possible motor overloading can
occur.

12. Unit Startup. Turn on power disconnect, turn on unit
either from controls or by Jumping 24v+ from
transformer (blue low voltage wire) to terminal #1.
Check that motors are spinning the right direction (3
phase units only) that the enthalpy wheel is spinning
and that motorized intake air and exhaust dampers are
opening.

If unit is operating properly proceed to next step, if not
operating properly See Trouble shooting guide on
Page 4.

13. Clean up, caulk any open joints, holes or seams to
make the unit completely air and water tight. Remove
any jumpers, replace all access panels on the unit and
secure.

14. Leave this instruction manual with the owner or in an
envelope near the unit.

See System Check or Trouble shooting guide for
further information on the proper operation of the
ERV.

PAGE 2

VIII - Stand Alone ERV Controls Schemes
Dependent options
Thermostat: This is the standard way to wire an ERV,

when the ductwork of the stand alone ERV is attached to
the ductwork of a single AC system the controls of the ERV
should be wired in parallel with the controls with "G" to 1,
"C" to 2 and "W" to 3. The ERV will operate when ever the
RTU's blower is operating.

Energy Management – Building Management Systems:
The ERV needs a 24 Volt AC signal to operate, connect the
24V+ to 1 and the 24V C to 2, the unit can be operated off of
a relay or BMS controller if necessary.

Dedicated options

When using a control method that does not involve an
outside 24V controls signal power can be borrowed from
the unit's transformer for short thermostat wire runs. Any
run over 150' however should be powered by a separate
transformer.

Thermostat: When using an ERV to service a large area
with multiple AC units or when not tying directly into the
ductwork of a single AC system the ERV can be run off of
its own Thermostat. Splice the 24V+ wire "R" onto the
XFORMER + terminal of the ERV control board, then wire
"G" and "C" onto terminals 1 and 2 respectively, program
Thermostat to energize G when space is occupied.

CO2 Sensor/ Transmitter: An ERV can be wired to a wall
mounted CO2 Sensor/ Transmitter with relay like Johnson
Controls CD-WR0-00-0 (or CD-WRD-00-0) in order to
operate the ERV when ventilation is required due to high
CO2 levels. This type of transmitter has an adjustable set
point, and a relay that the 24V+ signal can be wired into
and "G" wire can be wired out of. "G" should be wired to #1
terminal. The ERV will then turn on and provide fresh air to
the space to lower CO2 levels.

Quickstep: Units equipped with the Quick Step controls
option use an onboard microprocessor, factory installed
CO2 sensor and variable frequency drives to modulate
airflow through the ERV to control for Carbon Dioxide. To
operate the unit enter the Supply and Exhaust CFM values
(they do not have to be the same value) into the Quick Step
flexstat control along with maximum CO2 level and the
controls will modulate the blowers to ensure CO2 levels are
not above set point.

ON/OFF switch or Timer: Wire 24V+ from transformer
onto the input of the switch and connect the output of the
switch to terminal 1 on the control board. The ERV can be
turned on manually or be set to turn on at a regular
schedule when the building is occupied.

IX – Operation
How It Works.

The unit contains an energy recovery wheel (ERW) that is
a revolutionary concept in rotary air-to-air heat
exchangers. Designed as a packaged unit for ease of
installation and maintenance, only the connection of
electrical power is required to make the system
operational.

When slowly rotating through counter flowing exhaust and
fresh air streams the ERW absorbs sensible heat and
latent heat from the warmer air stream in the first half of its
rotation and transfers this total energy to the cooler air
stream during the second half of this rotating cycle.

Rotating at 50-60 RPM, the ERW provides a constant flow
of energy from the warmer to the cooler air stream. The
large energy transfer surface and laminar flow through the
ERW causes this constant flow of recovered energy to
represent up to 85% of the difference in total energy
contained within the two air streams.

Sensible and latent heat are the two components of total
heat, sensible heat is energy contained in dry air and latent
heat is the energy contained within the moisture of the air.
The latent heat load from the outdoor fresh air on an air
conditioning system can often be two to three times that of
the sensible heat load and in the winter it is a significant
part of a humidification heat load.

During both the summer and the winter, the ERW transfers
moisture entirely in the vapor phase. This eliminates wet
surfaces that retain dust and promote fungal growth as well
as the need for a condensate pan and drain to carry water.

Because it is constantly rotating when in the air stream, the
ERW is always being cleaned by air, first in one direction
and then the other. Because it is always dry, dust or other
particles impinging on the surface during one half of the
cycle are readily removed during the next half of the cycle.

During the heating season, when outdoor air temperatures
are below 15oF, it is recommended to use the (optional)
low ambient kit.

Optional Kits

Motorized Intake Air Damper

This damper mounts inside the outdoor air intake hood, it
opens when the ERV supply blower is energized and
closes when de-energized.

Motorized Exhaust Air Damper

Damper mounts inside the exhaust air hood, it opens when
the ERV is energize and closes when the ERV is
de-energized.

Pressure Sensors

Measurement devices (Magnahelics) on ERV that
measure pressure across the energy recovery wheel.

Rotation Sensor
A magnetic sensor and logic board that measure pulses
from a magnet on the spinning energy recovery wheel. A
lack of measured pulses after initial start up results in an
alarm. The alarm can be wired into building management
hardware or to a thermostat with alarm switch terminals, it
will warn that the wheel has stopped spinning, but does not
otherwise effect operation.

Stop, Start, Jog [Climate Smart]

This option adds an Economizer or free cooling mode to
the ERV. The wheel stops spinning to allow air to pass
without energy transfer, starting and spinning
intermittently in order to keep the wheel clean.

Low Ambient Kit

Prevents frost buildup on energy recovery wheel by
terminating intake air when the discharge air temperature
falls below a set level. Intake blower operation resumes
after a 16oF rise above the field adjustable set point.

The frost threshold is the outdoor temperature at which
frost will begin to form on the ERV wheel. For energy
recovery ventilators, the frost is typically below 10oF. Frost
threshold is dependent on indoor temperature and
humidity. The table shows how the frost threshold
temperatures vary depending on indoor conditions.

PAGE 3

FROST THRESH OLD TEM PER A TURE

IN DOOR RH AT 70oF

20% 0oF

30% 5oF

40% 10oF

FROST THRESH OLD

TEM PER A TURE

Because energy recovery ventilators have a low frost
threshold, frost control options are not necessary in many
climates. The Low Ambient Kit is available for units
installed where outdoor temperatures may drop below the
frost threshold during the ERV operational hours.

Filter Racks/ Filter Options

Stand alone units come with return air filters standard,
MERV 8, 11, or 13 filters can be ordered with the unit.
Supply air filter racks can be added as an option with the
same efficiency filter options.

Dirty Filter Switches

Pressure differential switches that can be hooked up to an
alarm to alert when pressure drops across a filter bank
indicating dirty or clogged filter, they do not otherwise
effect operation.

Wheel Type

While the standard energy recovery wheel absorbs both
sensible and latent heat a sensible only wheel can be
ordered for applications where the sensible portion of the
heat load needs to be removed from a space without
returning the humidity.

Smoke Detector

Smoke detectors can be factory ordered with the ERV, a
qualified technician needs to field wire the smoke detector
into the controls to break common in case of alarm.

CO2 Sensor
See Quickstep in Controls schemes. A factory installed
Co2 sensor can be added to the unit to adjust ventilation on
a CO2 parts per million demand. This sensor is mounted
next to the return air inlet and is not a relay, it only provides
feedback to the quick step controls to adjust motor speed
and is not suitable to turn the unit on and off on CO
demand.

X – System Check

1. Disconnect main power

2. On units controlled by thermostats turn T-stat fan
switch to "On". Otherwise jump 24v+ to terminal #1.

3. Restore power to unit, observe ERV wheel rotation
and both fresh air and exhaust air blowers.

Note: If the low ambient kit is used the jumper between

terminals 5&6 should be removed and replaced
with blue and yellow wires for the sensor. If system
check out is being done at low ambient
temperatures this kit can cause the unit not to
operate. Under these conditions jump terminals
5&6.

4. Verify the ERV three phase blower motors are phased
sequentially ensuring correct rotation and operation. If
both blowers are running backwards:

A. Disconnect Power.

B. Reverse and two high voltage line in wires on the

ERVs fuse block.

C. Reapply Power.

Note: Blower Motor rotation is checked in factory, do

not switch wires at contactors or on motors if
blowers are spinning backwards at startup.

5. Verify that both blower motors are operating under
their full load AMP rating (FLA). The FLA can be found
on each motor and on the unit's name plate.

6. Verify that the fresh air and exhaust air motorized
dampers are opening and closing when unit turns
on/off.

Note: If unit is not operating properly refer to

troubleshooting guide.

7. Return damper settings. When tied into an HVAC
system manually adjust the position of the field
installed dampers to balance Air flow.

8. Static test ports are provided to verify intake and
exhaust CFM, these ports can also be used with a
temperature probe to verify temperature transfer
through the wheel.

Adjustment to the blower speed is accomplished by
changing the sheave setting on both fresh air and exhaust
air blowers.

Flow / Blower Speed Ad just ment

Blower speed selection is accomplished by changing the
sheave setting on both fresh air and exhaust air blowers.
To set ERV for the required air flow (CFM), the external
static pressure applied to the ERV (duct static) must be
known. See the CFM vs External Static Pressure chart for
the appropriate unit to determine the correct blower RPM
for the specified CFM and External Static Pressure.

After blower speed adjustments have been made. Ensure
that when the belt is replaced it is tensioned correctly. The
motor mounting plate can be adjusted to tension the belt. If
using a belt tension checker, adjust the span to the
appropriate setting and check the belt defection force. The
belt deflection force should be between 5-8 lbs or the
lowest tension at which the belt will not slip under peak load
conditions.

2

1. Disconnect main power to unit before making
adjustment to economizer and/or ERV unit.

2. Replace ERV control access cover.

3. Set thermostat to normal operating position.

4. Restore power to unit.

XI - Se quence of Op er a tion

1. The thermostat or Building Management System
(BMS), sends a 24 Volt AC signal to the HVAC system
for cooling, heating, fan only or ventilation operation.

2. The ERV is activated simultaneously with the blower of
the AC system. The intake air blower, the exhaust
blower and the enthalpy wheel motor of the ERV are
activated, these motors will remain energized as long
as the blower in the AC system is energized and the
outdoor conditions are adequate for energy recovery.

3. If the optional motorized intake air damper is present,
the damper must open causing a proving switch to
close in order to energize the intake air blower (10-20
seconds after the exhaust blower and enthalpy wheel
have started).

4. If the optional low ambient kit is present, and the
temperature leaving the exhaust side of the enthalpy
wheel is lower than the field adjusted set point on the

PAGE 4

temperature sensor, the optional motorized fresh air
damper will close and the intake blower will
de-energize. The exhaust blower and enthalpy wheel
motor will continue to operate until the temperature
sensor has a 16F rise, at this point the enthalpy wheel
should be defrosted and the optional motorized
damper will open and the fresh air blower will
reactivate.

5. If the start, stop, jog [Climate Smart] option is present
and outside conditions are adequate for free cooling
the enthalpy wheel motor will stop for 10 minutes to
allow for cool air to enter the building. It will then start or
jog the wheel for 1 minute to keep dirt from building up
on the wheel.

XII - Trou ble Shoot ing guide
ERV will not op er ate:

1. Quick check items.

A. Verify that the door switch is closed, the switch

must be in the closed position in order to power
the control board.

B. Verify 24V power to the control board at terminals

Xformer + & -. If voltage is low check high voltage
into the unit (sec 2-A) and check that the T-1 wire
from the high voltage into the step down
transformer is on the correct terminal
(208v-230v-460V) for the units voltage.

C. Verify 24V to the control board's terminal strip at

T-1 (G) and T-2 (Com) in Fan or Cool or T-2 (Com)
and T-3 (W) in Heat. These terminals must be

powered by an external power source to
operate the ERV.

A jumper from Xformer + to T-1 can be used to test
operation of the ERV if an external 24V controls signal is
not available.

1. Verify high voltage to ERV

A. Verify that the unit has the proper voltage in at

terminals L1, L2 and/or L3 at the fused high
voltage connection terminal block. Voltage
specifications are on the units name plate.

B. Verify that the fuses are good, (check voltage

across fuses with power on, voltage should be 0)
replace any bad fuses.

ERV Has Power, But Motors Are Spinning Backwards

1. Motors are checked for proper rotation at the factory, if
the motors are spinning backwards after install
reverse the phase by switching two wires on the high
voltage IN terminals.

2. If the motor is spinning backwards after replacement
switch the L1 & L2 wires connected inside the motors
access panel. Do no rewire unit.

*Many of motors used in production of the ERVs are multi
voltage (230/460V) motors. When replacing motors or
diagnosing a motor that won't start. Care should be taken
to make sure the wires inside the motors access panel are
connected securely and in the proper configuration.

ERV Has Power, But the Enthalpy Wheel Does Not
Spin (Start Stop Jog #1)

1. If the unit has the Start, Stop, Jog option installed the
enthalpy wheel motor will turn off for 10 minute
intervals when outside conditions are optimal for free

PAGE 5

cooling, the fresh air and exhaust blowers will continue
running. The Start, Stop, Jog control board has a white
test button that when pressed will bypass the boards
logic and turn the enthalpy wheel on. See Start, Stop,
Jog in Options/Accessories troubleshooting for further
information.

2. With the power off, check that the wheel belt is in place
and tight.

3. Check for 24 volts between terminals Exhaust (K163)
A&B, if the unit doesn't have Start, Stop, Jog the relay
is connected directly to the Exhaust A and B terminals
on the control board. If terminals 1&2 or 3&2 are
energized with 24V, there is 24V in to Xformer + & - ,
and there is no voltage to Exhaust A&B the board is
bad.

4. If there is 24 Volts at Exhaust A&B trace wires to the
enthalpy wheel relay, check terminals A&B on the
Relay for 24 Volts, check for high voltage power into
and out of the relay. If the relay is energized/closed
and no power is passing from terminals 7 to 4 or 9 to 6
the relay is bad.

5. You can jump the enthalpy wheel relay to test its
operation by running a jumper from the 24v out on the
transformer (blue wire) to the A terminal on the relay
after removing the pink wire.

6. If the relay is closing and there is proper voltage
between terminals 4&6 on the relay check the wheel's
motor for proper voltage by using a multi-meter at Plug
P-150 next to the enthalpy wheel motor.

A. If voltage is present and this is a single phase

motor (most units) check the motor's capacitor.

B. If the capacitor is bad replace the capacitor,

continue testing the motor

C. If proper voltage is present and the capacitor is

good check the wires into the motor for continuity,
if there is no continuity through the windings a wire
connection is loose or the motor is bad, check wire
connections between harness and windings, if
connections are good the motor is bad, replace
motor.

ERV Has Power But the Exhaust Blower Does Not
Operate

1. With power off. On units with belts, check that the
blower's belt is tight and in place, if it is loose adjust the
motor or sheave to tighten it, if it is broken replace it.

2. Check the contactor (K-163) to see if the issue is with
high voltage or low voltage, if the contactor is closed
check the motor. If it is open, push closed to check that
the motor starts then check controls

3. Check for 24 Volts between Exhaust A&B terminals on
the control board.

A. If the controls are calling for operation but there are

not 24 Volts between Exhaust A&B the board is
bad.

B. If the controls are calling for operation and there

are 24 Volts between Exhaust A&B check the
yellow wire for direct connection to the proper
contactor (K-136), then check the pink wire for
continuity through the field installed exhaust
damper motor (if option was chosen) or the factory
installed plug (PK-3) at the Jack (J-161) located in
the exhaust blower section.

3. If contactor is closed check voltage to the motor by
testing wires at Plug P-151, proper voltage is listed on
the unit's information tag. If there is proper voltage to
the motor and the motor is not spinning the motor is
bad. With single phase units check the capacitor, if
capacitor is bad replace it then continue checking the
motor.

ERV Has Power But The Intake Air Blower Does Not
Operate

1. With power off. On units with belts, check that the
blower's belt is tight and in place, if it is loose adjust the
motor or sheave to tighten it, if it is broken replace it.

2. Check the contactor (K-164) to see if the issue is with
high voltage or low voltage. If the contactor is closed
check the motor. If it is open, push closed to check that
the motor starts, then check controls.

3. If the contactor is open check for 24 Volts between
Fresh A&B terminals on the control board.

A. If the controls are calling for operation and there is

no voltage between Fresh A&B check terminals
5&6 to see if low ambient kit is installed (blue and
yellow wires installed instead of a jumper),
jumping terminals 5&6 will bypass the low ambient
sensor and energize terminals Fresh A&B. See
Low Ambient Kit in Options/Accessories
troubleshooting for further information.

B. If the controls are calling for operation and there is

no voltage between Fresh A&B and there is
continuity between terminals 5&6 then the board
is bad.

C. If the controls are calling for operation and

terminals Fresh A&B are energized but the
contactor is not energizing, check the yellow wire
from terminal Fresh B to contactor (K-164), check
the orange wire for continuity from terminal Fresh
A through factory installed fresh air damper plug
(P-160) to contactor. In models without a fresh air
damper option there should be an orange jumper
between pins 3&4 on the P-160 plug, when the
fresh air damper option is chosen these wires
connect to an end switch that is closed by a cam
when the fresh air damper opens. See Sequence
of Operations.

1. If contactor is closed check voltage to the motor by
testing wires at plug P-148, proper voltage is listed on
the unit's information tag. If there is proper voltage to
the motor and the motor is not spinning the motor is
bad. With single phase units check the capacitor, if
capacitor is bad replace it then check the motor.

ERV Has Power But The Motorized Fresh Air Damper
Does Not open

1. Verify 24V in between terminals 1&2 or 3&2

2. Check voltage at junction J-56 on the ERV control
board, there should be 24V between J-56 1&2 during
normal operation, If the unit has a low ambient kit
installed and temperatures are low the controls
de-energize J-56 and Fresh K-164 terminals on the
control board, jump Terminals 5&6 on the Terminal
strip to bypass see Low Ambient Kit in
Options/Accessories Troubleshooting for further
information.

3. If there is voltage at the control board check for 24V at
plug P-160 between pins 1&2

4. If there is voltage at P-160 make sure the damper
linkage isn't binding and that the wires are attached to
the actuator firmly. If the actuator still doesn't move
when 24V is applied replace the actuator.

ERV Has Power But The Motorized Exhaust Air
Damper Does Not Open

1. Verify 24V In between terminals 1&2 or 3&2

2. Check voltage at Exhaust A&B on control board

3. If there is voltage at Exhaust A&B on the control board,
trace wires to the exhaust blower compartment and
plug P-161, Check for 24V between Pins 1&3.

4. If there is 24V at plug P-161 make sure the field
connected P-161 plug for the damper is inserted firmly
into J-161, that the damper linkage isn't binding and
that the wires are connected firmly to the actuator. If
the damper actuator still does not move the actuator is
bad.

Options and Accessories Troubleshooting

Start, Stop, Jog [Climate Smart]

The Start, Stop, Jog kit is an optional control board with
temperature and/or enthalpy sensor(s) that stops the
enthalpy wheel from spinning (and transferring heat) when
temperature conditions are conducive for free cooling. The
board will spin the wheel intermittently in 10 min off 1 min
on intervals to keep dust from building up on the surface.

All units shipped with the Start, Stop, Jog option installed
have the temperature and enthalpy sensors installed, and
the jumper (J9) set to T(emp). A qualified tech can adjust
the setting to E(nthalpy) only or Temp and Enthalpy by
adjusting the jumper (J9).

The factory set points to allow for free cooling during
ventilation are 40F-70F, but they can be field adjusted to
narrow the band by adjusting two potentiometers while
measuring VDC between the Com & High or Com & Low
terminals (0 VDC = 40 degrees, low set point, 5 VDC = 70
degrees, high set point).

Low Ambient Kit

The low ambient kit is an optional temperature probe on a
normally closed switch that closes the fresh air damper
and turns off the fresh air blower when temperatures in the
blower compartment suggest a frosted enthalpy wheel.
The adjustable sensor is factory set for 20F. The sensor is
mounted in the blower compartment with its probe near the
blower's inlet, it is wired into the terminal strip 5&6
terminals.

It can be tested in hot weather by turning the dial up to a
higher temperature and checking to see if the normally
closed relay opens. In cold weather if the "R" terminal and
"W" terminal in the sensor show an open circuit the bulb
can be warmed above the set-point at which point the relay
should close.

Dirty Filter Switch

Dirty filter switches are an optional kit that put an
adjustable pressure switch with the Low inlet on the blower
side of the filter and the High inlet connected to the far side
of the filter via tubing. A dirty filter moves less air lowering
the pressure on the fan side Low inlet closing the normally
open sensor switch and allowing an alarm. The sensor(s)
are prewired into their own terminal strip and can be field
wired in series (normally closed), in parallel (normally
open) or individually to an alarm device.

PAGE 6