Airxcel Marvair Scholar III VAIA Series Manual

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MAINTENANCE &
SERVICE
SIII M&S 8/09-1
Model VAIA
2, 2.5, 3, 3.5, 4 & 5
Tons
CAUTION!!
Read all instructions before use.
Retain this manual for future
reference. This equipment should
be installed and serviced only by a
trained professional HVAC service
person.
Due to continuous product
improvement, use only the current
issue of this manual. The latest
version can be downloaded from the
Marvair website - www.marvair.com.
Unitary Air-Conditioners AC
Unitary Air-Source Heat Pumps HP
Scholar III™
Heat Pumps & Air Conditioners
(CSI 15740)
Scholar III™
Manufactured By:
Marvair®Division of AIRXCEL®, Inc.
P.O. Box 400 • Cordele, Georgia 31010
156 Seedling Drive • Cordele, Georgia 31015
[phone] • Fax [phone]
E-mail: [email protected] • Internet: www.marvair.com

Scholar IIITM (M&S) 8/09-1 15700 - 2 HVAC Equipment
SECTION 15700
HEATING, VENTILATING AND AIR CONDITIONING EQUIPMENT
MAINTENANCE & SERVICE MANUAL
FOR SCHOLAR IIITM HEAT PUMP & AIR CONDITIONER, MODEL VAIA (CSI 15740)
TABLE OF CONTENTS
Chapter Description Page
1.1 General Description ..................................................................3
1.2 ModelIdentication ..................................................................4
2.1 Start-up Instructions.................................................................5
2.2 Ventilation System Calibration....................................................7
3.1 Electrical..................................................................................9
4.1 Maintenance ..........................................................................14
5.1 Function & Description of Primary Components.........................14
6.1 Troubleshooting......................................................................26
7.1 Service ..................................................................................36
8.1 Filing a Service/Warranty Claim ...............................................55
9.1 Warranty Statement................................................................56
10.1 Exploded Views and Parts List .................................................57

Scholar IIITM (M&S) 8/09-1 15700 - 3 HVAC Equipment
SECTION 15700
HEATING, VENTILATING AND AIR CONDITIONING EQUIPMENT
The purpose of this manual is to provide instructions for maintenance and service for the
Marvair®Scholar III™ series of heat pumps and air conditioners. In addition to this manual,
there are other pieces of literature available from Marvair. The Engineering and Design Manual
details the design and selection of HVAC systems using the Scholar III series. The Installation
and Start-Up manual covers the installation of the unit and various accessories and the initial
start-up of the unit. An overview of the product line can be found in the Heat Pump and Air
Conditioner Product Data Sheets. The current version of this literature can be found and down-
loaded from the Marvair website at www.marvair.com.
To minimize sound levels within the classroom, certain options should be selected. These op-
tions are designated by throughout the guideline.
1.1 GENERAL OPERATION
A. Scholar III™ heat pumps and air conditioners are designed to provide quiet comfort
to the classroom.
In cooling mode, the compressor will cycle on to provide the cooling required. The
systemprovidescooling,dehumidicationandaircirculation.
In heating mode the compressor (heat pump only) will cycle on to provide the
heating required. The system provides heating and air circulation. At lower outdoor
temperatures, additional heating capacity may be provided by an optional electric
resistance heater or a hot water/steam coil.
Ventilation air may be provided by the manual or motorized fresh air vent, power
vent or GreenWheel®ERV. These ventilation systems operate when there is a call
for cooling or heating or independently to provide fresh air. Note that with the
manual, motorized fresh air vent and the power vent options, if the compressor is
not operating and the indoor blower is running, unconditioned outside air is being
introduced into the classroom. The GreenWheel ERV provides tempered outside air.
Control systems are either a remote external thermostat, internal thermostat, or a
direct digital control interfacing with the building automation system (BAS).
 HotGasReheat(HGR)Dehumidication(Option).Toprovideondemand
dehumidication,theScholarIII™heatpumporairconditionercanhaveafactory
installedhotgasreheatcoiltoallowdehumidicationthroughcontinuedcooling
with discharge air reheated to avoid over cooling the classroom. The hot gas
dehumidicationoptioncanbeusedwithelectric,steamorhotwaterheat.The
operation of the HGR is controlled by a three-way heat reclaim valve. The HGR coil
is sized to provide a heating capacity approximately equal to the sensible capacity of
the unit Whenthedemandforcoolingissatisedandthehumiditycontrollercallsfor
dehumidication,hotgasisdirectedtoareheatcoildownstreamfromtheevaporator
coiltoaddheattothedehumidied,chilledairsuppliedtotheclassroom.Hotgas

Scholar IIITM (M&S) 8/09-1 15700 - 4 HVAC Equipment
1.2 MODEL IDENTIFICATION
The Scholar IIITMheatpumpandairconditioneridenticationnumberingsystemis
shownbelow.Themodelidenticationnumberisonthedatalabel.Thedatalabelisat
the bottom of the of left side panel.
IMPORTANT
WHENSCHOLARIIITMSYSTEMSAREINSTALLED,MODELNUMBERANDSERIAL
NUMBERSARETOBERECORDEDANDMAINTAINEDINALOCATIONFOR
IMMEDIATEACCESSWHENREQUESTINGFURTHERINFORMATION.
Source
Vertical
Air
Indoor
Nominal Cooling
System Type
HP = Heat Pump
AC = Air Conditioner
Power Supply
A=208/230V,1,60Hz
C =208/230V,3,60Hz
D= 460V,3,60Hz
Configuration
N= Manual Damper (std)
H=GreenWheel®ERV
B =Motorized Damper
J =Power Vent with
Motorized Damper Special Options
G =Hot Gas Reheat/Dehumidification
•••• •
VA I•III
Configuration
III = Scholar III
2-Stage
Compressor
S
Refrigerant
R-410A
A
24 = 24,000 BTUH
30 = 29,000 BTUH
36 = 35,000 BTUH
40 = 40,500 BTUH
48 = 48,000 BTUH
60 = 59,000 BTUH
Heat – kW
000 - No Heat
050 = 5 kW
075 = 7.5 kW
100 = 10 kW
150 = 15 kW
099 = 99 (Hot Water)
Q=GreenCube™ ERV
reheat is available with motorized fresh air, PowerVent and GreenWheel®ventilation
systems.
Marvair®recommends that for optimum performance, hot gas reheat be used in
conjunction with the GreenWheel®heat recovery ventilator. When used with other
ventilation options, hot gas reheat may not maintain satisfactory control of the
humidity in the classroom over all outdoor conditions.
Figure 1. Conditioned Air Flow and Fresh Air Flow

Scholar IIITM (M&S) 8/09-1 15700 - 5 HVAC Equipment
3. TurntheScholarIII™disconnectto“ON”position.
4. Cooling
a. Settheremotethermostatsystemswitchto“OFF”position.Theblower
switchshouldbein“AUTO”position.
b. At the remote thermostat, raise the cooling set point several degrees above
room temperature. Lower the “heating” set point several degrees below room
temperature.
c. Move the blower switch on the remote thermostat from “AUTO” to “ON”
position. The indoor blower should come on, as evidenced by sound and air
blowing out of the air supply grille.
d. Move the blower switch on the remote thermostat from “ON” to “AUTO” and
the indoor blower will stop 90 seconds later.
e. Move the system switch on the remote thermostat from “OFF” to “COOL.”
Slowly lower the cooling set point to just below room temperature and bring
on cooling. Check to see that when the heat pump comes on that the air
coming out the discharge grille is cooling. Let unit run for ve minutes in this
mode. If heat pump continues to run and provide cooling, this veries that
the indoor blower, compressor and outdoor blower are all running.
2.1 START-UP PROCEDURE
A. This start-up procedure applies to Scholar III™ models equipped with a remote (wall
mounted) thermostat and electric supplemental heat.
1. TurnthedisconnectintheScholarIII™unitto“OFF”positionanddoublecheck
all electrical connections before applying power.
2. Checkthevoltagesupplytothedisconnect.Ifvoltagereadingsareappropriate,
proceed with start-up. (See Figure 2 for acceptable voltage ranges.) If voltage
readingsarenotappropriate,checkthepowerleadsatthedisconnectandthe
mainbreakerinthemechanicalroom.Takeappropriatecorrectiveactionto
supplysufcientvoltagetotheScholarIII™disconnect.
Figure 2. Voltage Limitations
*Letters refer to model number code designations.
Example: VAIA 36 HP A Voltage
Electrical Voltage Designations* A C D
Nominal Voltage 208/230 208/230 460
Phase 13 3
Minimum Voltage 197 197 414
Maximum Voltage 253 253 506

Scholar IIITM (M&S) 8/09-1 15700 - 6 HVAC Equipment
f. Now slowly raise the cooling set point up toward room temperature until the
pump compressor and outdoor blower motor turn off. This will be audible.
The indoor blower will continue to run and turn off after 90 seconds.
5a. Heating (heat pump version only)
a. Put the thermostat system switch to “HEAT” mode. Wait ve minutes after
testing on cooling, before testing in heating mode.
b. Slowly raise the heating set point above room temperature until the heat
pump comes on. The indoor blowers will start and the heat pump will
provide warm air from the air supply grille. Let run for ve minutes.
c. Slowly lower the set point temperature until the heat pump compressor and
outdoor blower turn off. The indoor blower will turn off 90 seconds later.
5b. Heating (air conditioner version only)
a. Set the heating set point below room temperature and put the thermostat
system switch on “HT.”
b. Raise the set point slowly and the indoor blower and the electric
supplemental heat will turn on at the same time.
c. Lowering the set point slowly should turn the electric heat off. The indoor
blower will turn off 90 seconds later.
6. Automatic Changeover
For an automatic changeover remote thermostat, the proper functioning of the
systemcanbecheckedforcoolingandheatingbyusingthesamesequenceas
detailedabovewiththethermostatsystemswitchputin“AUTO”position.
7. Emergency Heat (heat pump version only)
This setting on a remote thermostat is to provide electric heat in the event the
compressor does not function, and heat is required. In emergency heat mode,
the compressor is de-energized and electric heat supplies all heating, controlled
by the thermostat.
 Tocheckthisout,settheheatingsetpointbelowroomtemperatureandputthe
thermostat system switch on “EM. HT.”
Raise the set point slowly and the indoor blower and the electric supplemental
heat will turn on at the same time.
Lowering the set point slowly should turn the electric heat off. The indoor blower
will turn off 90 seconds later.

Scholar IIITM (M&S) 8/09-1 15700 - 7 HVAC Equipment
2.2 VENTILATION SYSTEM CALIBRATION
The ventilation system requires calibration to ensure the appropriate amount of
fresh air is delivered to the classroom. Refer to the appropriate following ventilation
system and use the instructions to calibrate the system for correct air delivery.
A. Manual Fresh Air System. Fresh air ventilation by means of a damper with pressure
relief(openingtooutside,butnoexhaustblower),aventilationintakeblowerand
a fan speed controller provides up to 450 cfm of outside air. The damper can be
manuallyadjustedatinstallationtoprovidetherequiredventilationairow.
The fresh air door should be set in accordance with the amount of fresh air ow
required, up to a maximum of 450 CFM. Figure 3 illustrates the fresh air door
settings and air ow rates.
Follow the directions in Figure 3 to ensure proper air ow rate settings.
B. Motorized Fresh Air-CongurationB.Thisventilationoptionincludesamotorized
damper,afreshairintakeblowerandmotor,andablowermotorspeedcontroller.
This ventilation option can provide up to 450 CFM of outside air (but not to
exceed40%ofratedairow)andincludespressurerelief(openingtooutside,
but no exhaust blower). The motorized damper and blowers are controlled by
a Programmable Logic Controller (PLC). The PLC will operate the damper and
ventilationmotorsONLYwhentheIndoor/Evaporatorblowerisoperating.ThePLC
is factory wired for this operation by a 24 VAC signal to an input terminal on the
PLC. The damper is adjusted after installation for the required rate of ventilation. An
optional 24 VAC, 120 VAC or 240 VAC coil relay may be factory installed to control
thedamperandmotorfromanexternalsignal,e.g.anEMSorBASsystem.Alter
on the incoming outside air is standard.
PowerVent-CongurationJ(Optional).Thisventilationoptionincludesamotorized
damper,afreshairintakeblowerandmotor,anexhaustairblowerandmotorand
one blower motor speed controller. The blower speed controller operates both
blowers in tandem. (An optional blower speed control for the exhaust air blower can
be factory installed to provide independent control of the exhaust air blower motor
and allow pressurization of the classroom).The PowerVent can provide up to 450 CFM
ofoutsideair(butnottoexceed40%ofratedairow)andincludesactivepressure
relief. The motorized damper and blowers are controlled by a Programmable Logic
Controller(PLC).ThePLCwilloperatethedamperandventilationmotorsONLYwhen
the Indoor/Evaporator blower is operating. The PLC is factory wired for this operation
by a 24 VAC signal to an input terminal on the PLC. The damper is adjusted after
installation for the required rate of ventilation. An optional 24 VAC, 120 VAC or 240
VAC coil relay may be factory installed to control the damper and motor from an
externalsignal,e.g.anEMSorBASsystem.Alterontheincomingoutsideairis
standard.
The fresh air door is opened and closed by the motorized drive. Calibration, as
shown in Figure 4, will ensure the required amount of air, up to a maximum of 450
CFM, is delivered to the classroom.

Scholar IIITM (M&S) 8/09-1 15700 - 8 HVAC Equipment
Figure 4. Motorized and PowerVent System Calibration Procedure
Inside the lower section, locate the circular calibration plates as
noted above in the drawing (“A” is xed, “B” is movable). Remove
the screw shown by the arrow from “motorized settings.”
Reinsert the screw into the hole in plate B adjacent to the
desired air ow rate, in CFM, and rmly drive the screw in until
it bottoms out at the screw head.
Figure 3. Manual Fresh Air System Calibration Procedure
Inside the lower section, locate the circular calibration plates
as noted in the drawing (“A” is xed, “B” is movable). Remove
the screw shown by the arrow from “Manual Settings.”
Rotate plate B in a clockwise direction until the hole from
which the screw was removed aligns with the hole adjacent
to the desired air ow rate, in CFM.
Reinsert the screw into the hole in plate B and rmly drive
the screw through the appropriate air ow rate hole, so plate
B is securely fastened at the desired opening.
Follow the directions in Figure 4 to ensure the proper air ow rate setting. After
calibrating the ventilation system, replace the lower front cabinet panel.
C. GreenWheel®ERV. Using best industry standards and practices, measure the fresh
air that is being brought into the classroom. For units with one speed controller
(std.),adjustthespeedoftheintakeandexhaustblowersbyinsertingaslotted
screw driver into the opening on the controller. The speed controller is located in
thecontrolbox.Measuretheintakeairagainandadjustthespeedoftheblowers.
Repeat as necessary to meet the fresh air requirements.
For units with the optional variable fan speed controller for the exhaust blower on
the GreenWheel®ERV,rstmeasuretheairbeingintroducedintotheclassroom
using best industry standards and practices. Adjust the speed of the intake air blower
until the required outside air is being brought into the classroom.
Now measure the exhaust air from the classroom. Adjust the speed of the exhaust
air blower until the required air is being exhausted from the classroom. The exhaust
air controller is in the control box. It is usual practice to pressurize the classroom by
exhausting slightly less air than is being brought into the classroom.

Scholar IIITM (M&S) 8/09-1 15700 - 9 HVAC Equipment
3.1 ELECTRICAL
Figure 5. Typical Control Center Layout for Models VAIA24/30/36/40
Scholar III heat pumps and air conditioners are built in a wide variety of congurations and
options. The illustrations of the control center and the electrical schematics shown here are typi-
cal, but probably are not identical to your units. Please refer to the electrical schematic in each
unit for the specic construction of that unit.

Scholar IIITM (M&S) 8/09-1 15700 - 10 HVAC Equipment
Figure 7a. Typical Wiring Schematic for Heat Pump Model VAIA,
Single Phase Power

Scholar IIITM (M&S) 8/09-1 15700 - 11 HVAC Equipment
Figure 7b. Typical Wiring Schematic for Air Conditioner Model VAIA,
Single Phase Power

Scholar IIITM (M&S) 8/09-1 15700 - 12 HVAC Equipment
Figure 8a. Typical Wiring Schematic for Heat Pump Model VAIA,
Three Phase Power

Scholar IIITM (M&S) 8/09-1 15700 - 13 HVAC Equipment
Figure 9b. Humidity Controller Wiring Detail
Figure 9a. Remote Wall Mounted Thermostat Wiring Detail
THE INTERNAL TRANSFORMER IS NOT DESIGNED TO
POWER OTHER EXTERNAL DEVICES.
W2
G
X
HER
A
Y
O
W2
G
C
R
A
Y
O
HEAT PUMP*LOW VOLTAGE SECTION
Thermostat
Field Supplied
Seven (7) Conductor, Color Coded
18 Gauge Thermostat Cable
Humidity Controller
*A/C’s do not have “O”.
W2
G
X
HER
A
Y
O
W2
G
C
R
A
Y
O
Thermostat
Field Supplied
Seven (7) Conductor, Color Coded
Thermostat Cable
GeoScholar Heat Pumps
Note: A/C’s do not have “O”.

Scholar IIITM (M&S) 8/09-1 15700 - 14 HVAC Equipment
4.1 MAINTENANCE
WARNING
BEFORE PERFORMING MAINTENANCE ON THE SCHOLAR III™, SWITCH ELECTRIC
POWER OFF AT THE DISCONNECT LOCATED BEHIND THE RIGHT FRONT DOOR.
FAILURE TO DO THIS COULD RESULT IN PROPERTY DAMAGE,
BODILY INJURY OR DEATH.
A. Air lters on the Scholar III™ model VAIA require scheduled inspection and
maintenance. They should be inspected and cleaned or replaced twice a year, as a
minimum, before the heating and cooling season.
They should be inspected more often, as necessary.
 PleaserefertoChapter7.1forinstructionsonaccessingthereturnairlters.
The GreenWheel®Mediacanbecheckedvisuallyforexcessivedirtbuild-up.Ifthere
is residue build-up on the GreenWheel media, it can be vacuum-cleaned, in place, as
necessary.SeeChapter7FforaccesstotheGreenWheelforcleaning.Checkitand
vacuumcleanasnecessary.Alsochecktoseethattherubberdrivebeltisproperly
engaged on the GreenWheel and drive motor pulley.
B. Cabinet Panels/Indoor Grilles may be cleaned with a sponge and warm, soapy
water or a mild detergent. Do not use bleach, abrasive chemicals, or harmful
solvents.
C. If the Indoor Coils becomes clogged or dirty, it may be cleaned by careful
vacuumingorwithacommercialevaporatorcleaningspray.DONOTuseasolvent
containingbleach,acetone,orammablesubstances.Turnoffpowerbefore
cleaning. Be careful not to wet any of the electrical components. Be sure the unit
has dried before restarting. See Chapter 7.3 for instructions on cleaning the indoor
coils.
D. Outdoor Coils. Periodically inspect the outdoor condenser coil and the cabinet
air reliefs for dirt or obstructions. Remove foreign objects such as leaves, paper,
etc. If the condenser coil is dirty, it may be washed off with a commercial solvent
intendedforthispurpose.TURNOFFPOWERBEFORECLEANING!Besurethatall
electrical components are thoroughly dry before restoring power. See Chapter 7.4 for
information on cleaning the outdoor coils.
D. Condensate Lines. Each Scholar III™ air conditioner or heat pump has one
condensate line. The condensate line for the indoor and outdoor drain pans are tied
together and the condensate is discharged either through the base of the unit into a
oordrainoroutofthebackoftheunitatthebottomoftheunit.
5.1 FUNCTION AND DESCRIPTION OF PRIMARY COMPONENTS
A. Compressor. All Scholar™ units use a fully hermetic scroll compressor to minimize
soundlevelsandmaximizeefciency.Scrollcompressors,likeseveralothertypes
of compressors, will only compress in one rotational direction. The direction of

Scholar IIITM (M&S) 8/09-1 15700 - 15 HVAC Equipment
rotation is not an issue with single-phase compressors since they will always start
and run in the proper direction. However, three phase compressors will rotate in
either direction depending upon phasing of power. Since there is a 50-50 chance
of connecting power in such a way as to cause rotation in the reverse direction, it
isimperativetoconrmthatthecompressorisrotatingintheproperdirectionat
theinitialeldstart-upofthesystem.Vericationofproperrotationismadeby
observing that the suction pressure drops and the discharge pressure rises when
thecompressorisenergized.Analternatemethodofvericationforselfcontained
system with small critical refrigerant charges, where the installation of gauges may
be objectionable, can be made by monitoring the temperature of the refrigerant
lines at the compressor. The temperature should rise on the discharge line while the
suction line temperature decreases. Reverse rotation also results in a substantially
reduced current draw when compared to tabulated values.
There is no negative impact on durability caused by operating three phase
compressorsinthereverseddirectionforashortdurationoftime,usuallydened
as less than one hour. However, after several minutes of operation the compressor's
internal protector will trip. The compressor will then cycle on the protector until
the phasing is corrected. Reverse operation for longer than one hour may have a
negative impact on the bearings.
 Thecompressor,reversingvalveandcoil,andtheSchraderttingsarelocatedbehind
the hinged control box.Seegurebelow.
B. Indoor Blower and Motor. All Scholar III air conditioners and heat pumps use an
electronically commutated (EC) blower motor and a single blower. The motor speed
iscontrolledbyapulsewidthmodulatorlocatedintheelectricalboxandidentied
asIBM.Themodulatorsarefactorysetforproperairowfordesignrequirements.
Should the modulator need adjustment, use the following procedure.
 Onthefaceofthemodulator,thereisanadjustmentdialwithaslotinthemiddle.
 Usingaslottedscrewdriver,gentlyturnthedialclockwisetoincreasetheairowand
counterclockwisetodecreasetheairow.Whilerotatingtheadjuster,anumerical
owindexislockedonthedisplay.Afteradjustment,thedisplayshowsfanRPM.
COMPRESSOR
SCHRADER
FITTINGS
REVERSING
VALVE
CONDENSATE
TUBING

Scholar IIITM (M&S) 8/09-1 15700 - 16 HVAC Equipment
C. Outdoor Air Mover. The outdoor air mover is an axial fan with an asynchronous
external rotor motor on the 2, 2½, 3, & 3½ heat pumps and all air conditioners.
Scholar III heat pumps, models VAIA & VAISA 48 & 60 use two blowers with
electronicallycommutatedmotors(ECM).Oneoftheblowersoperatesafullspeed
anytime the compressor is on. A fan cycle switch on the second blower cycles the
blower on & off to maintain proper refrigerant pressures. The switch closes at 400
psig and opens at 245 psig.
 Eachblowermotoriscontrolledbyapulsewidthmodulator,identiedinthecontrol
boxbyOFM1andOFM2.Themodulatorsarefactorysetforproperairowfor
design requirements. Should the modulator need adjustment, use the following
procedure.
1. In the middle of each modulator there is a blue dial with a slot in the middle.
 2. Usingaslottedscrewdriver,gentlyturnthedialclockwisetoincreasetheairow
 andcounterclockwisetodecreasetheairow.
 ReadthesettingbywatchingtheLAMPashes.TheLAMPcontinuouslyashesout
thecurrentsetting.Afterapause,theLAMPashesoutthetensdigit,thentheunits
digit of a number (percent) between 1 and 99. If the lamp stays on, the setting is
100%.Longashesrepresentthetensdigit,andshortashesrepresenttheunits
digit.Asettingof23%willashtwolongs,andthreeshorts.TheLAMPfeaturecan
be used to record an air balance setting, or to precisely set the signal to the ECM
motor without using a meter.
 Theoutdoorcoils,lterdrier,highpressureswitch,lossofchargeswitchoutdoor
orice,defrostsensorarelocatedbehindthemiddlefrontdoor.
OUTDOOR
ORIFICES
DEFROST
SENSOR
FILTER DRIER OUTDOOR
COIL
LOSS OF
CHARGE
SWITCH
HIGH
PRESSURE
SWITCH
VENTILATION
DUCT

Scholar IIITM (M&S) 8/09-1 15700 - 17 HVAC Equipment
D. Indoor/Outdoor Coils.Thecoilsareconstructedoflanced,aluminumns
mechanicallybondedtoried,seamlesscoppertubes.
E. Filter Drier-Thelterdrierperformstwofunctionsintherefrigerantcircuit.First,
it removes foreign particulate matter, e.g. dirt, scale, solder particles from the
refrigerant to protect the compressor and other components in the refrigerant system
with small openings or close tolerances. Second, it absorbs any moisture in the
refrigerant with desiccant granules.
F. High and Low Refrigerant Pressure (Air Conditioner) or Loss of Charge
(Heat Pump) Switches & Optional (Heat Pump Only) Indoor Coil Freeze
Stat. These switches render the compressor and outdoor fan motor inoperative
whenever the limits of the high or low pressure switches are exceeded or indoor
coil freeze up. In the event of high pressure, the Scholar IIITM unit will turn off and
lockout.Thehighpressureswitchopensat610psigandresetsat420psig.
The system has a High Pressure Switch (HPS) that indicates a high system pressure.
Whenthisoccurs,thesystemwillrunforvesecondsthensetaHighPressure
Lockout.Thislockoutconditionshutsthesystemoffandashesthe“A”indicatoron
thePLCquicklyatarateoftwicepersecond.
The Low Pressure (air conditioner) or Loss of Charge (heat pump) switches are
designed is designed to guard against the operation of the system in the event
of a loss of refrigerant. If the Pressure (air conditioner) or Loss of Charge (heat
pump) switch opens for more than eight minutes, the system will turn off and a
LowPressureLockoutfaultwillbeindicatedbyaslowashingonthe“A”LED.The
intervalfortheashisoncepersecond.
In cold weather the pressure in the refrigerant system is low prior to operation.
When the Scholar III™ unit starts in the heat pump mode during cold weather, low
pressurecouldcausethesystemtolockout.Toguardagainstnuisancelockouts,the
Scholar III unit will not shut off if the Low Pressure Switch (LPS) comes on during
thersteightminutesofoperationandtheswitchhasnotcycledmorethanthree
times in an hour. In other words, the compressor will start and operate for eight
minutesevenwiththeLPSswitchopenthreetimesbeforecausingalockoutonlow
pressure.
Both switches open at 40 psig and close at 60 psig.
The high and low pressure switches are resettable at the wall thermostat or by
turning power off and then on to the Scholar IIITM unit. A fault LED located on
thePLCindicatesthatalockouthasoccurredandwhetheritisduetohighorlow
refrigerantpressureorindoorcoilfreeze-up.TheLEDwillashoncepersecondfor
lowpressureorindoorcoilfreezeuplockoutandtwicepersecondforhighpressure
lockout.
G. Metering Devices. The Scholar III uses a thermal expansion valve on the indoor
(cooling)circuitandaxedoriceontheoutdoor(heating)circuit.

Scholar IIITM (M&S) 8/09-1 15700 - 18 HVAC Equipment
H. Reversing Valve. Thereversingvalvereversestherefrigerant’sdirectionofowin
a heat pump, allowing the heat pump to switch from cooling to heating or heating to
cooling.
I. Exhaust Air Ventilation Blower is used to exhaust classroom in the GreenWheel
ERV and Power Vent ventilation options. The blower can exhaust up to 450 CFM
ofairfromtheclassroom.Inthestandardconguration,boththeexhaustandthe
intakeventilationblowersarecontrolledbyasinglespeedcontroller.Thisspeed
controller permits the motor speed to be adjusted for the correct cfm of ventilation
air. As an option, a second motor controller may be factory installed to allow
independentcontroloftheintakeandexhaustairblowers.Thisallowspressurization
oftheclassroom.Allventilationoptionshaveanintakeairblower.
J. Intake Ventilation Air Blower is used to introduce outside air into the classroom.
Inthestandardconguration,boththeexhaust(GreenWheelERVandPowerVent
only)andtheintakeventilationblowersarecontrolledbyasinglespeedcontroller.
This speed controller permits the motor speed to be adjusted for the correct cfm
of ventilation air. As an option, a second motor controller may be factory installed
toallowindependentcontroloftheintakeandexhaustairblowers.Thisallows
pressurization of the classroom.
K. Electric Resistance Heat is installed above the indoor blower outlet. Electric heat
iseldinstalledonallScholarIIIunits.Electricheatcanbeusedwiththefreeblow
plenum or with ducted air distribution options. The heaters are available in nominal
kWof5,10&15kWforoperationon208/230v.1Ø,208/230v.3Ø,and460v,3Ø.
The model number of the heat pump or air conditioner indicates the power supply
andkW.
L. Electric Resistance Heat Controls. Included with the electric heat assembly are
temperature switches designed to turn power off to the heaters if the temperature
istoohigh.Therearetwotypesoftemperatureswitches.Therstisanauto-reset
type that turns power off to the heater if it senses a temperature of 145°F. When
the temperature drops to approximately 105°F, power is restored to the heaters. This
auto-reset switch is in the low voltage circuit.
The second type of switch is a one time limit switch. If it senses a temperature of
300ºF,poweristurnedofftotheelements.ThisswitchdoesNOTresetwhenthe
temperature drops and must be replaced when it activates.
The number and location of both switches is determined by the power supply and the
kWoftheheaters.
M. Hot Water is installed above the indoor blower outlet as shown in the hot water
plenum. A diverter valve is a factory installed option with the hot water coil only. Hot
water heat is factory installed in the freeblow or the ducted plenums and is plumbed
from the top right side of the plenum. As a standard safety feature, each hot water
coil has a protective 24 volt freezestat embedded within it to trigger at 35°F and to
turn the unit off.

Scholar IIITM (M&S) 8/09-1 15700 - 19 HVAC Equipment
N. Programmable Logic Controller (PLC) Microprocessor. The Scholar IIITM heat
pump uses a factory installed PLC microprocessor to control the operation, the safety
switches and function options. LED’s show operational status and provide assistance
withdiagnosisiftroubleshootingiseverrequired.Variouscontrolfunctionsareeld
selectable. The PLC is also capable of communicating to other Scholar III unit PLC’s
to allow run time leveling and does not require additional equipment installed in
the Scholar III unit. The PLC microprocessor provides improved reliability because
of the reduction of components, the components utilized are more durable and the
controlboxwiringhasbeensimplied.Pertinentstatisticaldataaboutthelifeofthe
refrigeration system can be accessed through the PLC.
The PLC microprocessor provides for the following control and operation functions:
• Anti-Short Cycle Timer - Prevents the compressor from destructive short
cyclingduetomomentarypowerinterruptions.Oneofthreetimeintervalscan
beeldselected.
• Defrost Timer (heat pump only) - Adjustable defrost control that is based
upon both time and temperature. The time interval is adjustable from 30 to 90
minutes.
• BAS Control - Provides 24 VAC coil to control operation from Building
Automation System (BAS). Note - an additional BAS control relay can be added
when 120 or 240 VAC coils are required.
The unit control system is factory wired to operate upon an input signal from any
appropriate 24 VAC control thermostat or DDC control system. If unit shutdown
is desired during unoccupied periods of the temperature controlled space, it may
be accomplished by the following: the controls contractor must provide a set of
contacts(24VACpilotduty)betweenterminalsE1andE2.Whentheeldsupplied
contacts between E1 and E2 are closed the system will shutdown.
Location
The PLC is located in the unit control center. The control center is located behind a
panel in the lower right portion of the cabinet.

Scholar IIITM (M&S) 8/09-1 15700 - 20 HVAC Equipment
 OntherightsideofthePLCthereisasmalldoor.Behind
the door is a three position micro switch and two control
adjustments- an anti short cycle timer and a defrost
timer.Eachcontrolcanbeadjustedbyturningtheknob
withasmallatheadscrewdriver.Theindicatoronthe
knobisthegapbetweenthetwoprotrusionswiththe
hollowcentersontheknob.(Seedrawingbelow).For
bothcontroltimers,turningtheknobclockwiseincreases
thetimeperiod.NOTE:ScholarIIIairconditionersdonot
have the defrost function.
The micro switch has three positions – RUN, TERM &
STOP. The switch should be in the RUN position during
normal operation. Term is for operation from a remote terminal. Stop is no output/
non-operational.
The Anti-short Cycle Timer (ASCT) is located to the far left of the switch. The
anti-short cycle timer prevents the compressor from destructive short cycling by
allowing the compressor to restart only after a selected time interval has passed
from compressor shutdown. The timer begins when the compressor turns off. The
time interval is frm 3 seconds to eight minutes in one minute increments. The three-
second setting is used only for factory testing and should NEVER be used when
installedinaclassroom.Selectthedesiredtimeintervalbyrotatingtheknobtothe
desired setting. The Marvair® factory set point is 3 minutes.
The Defrost Timer (DFT) (heat pump function only) is located next to the three
position micro switch. The defrost control is based upon both time and temperature.
The DFT initiates a defrost cycle whenever the outdoor coil temperature is 28°F
or below and the selected time interval from the previous defrost cycle has been
exceeded.SelectthedesiredtimeintervalbyturningtheDFTknob.Whenturned
completelytotheleft(counterclockwise),thetimeintervalbetweendefrostcycles
is30minutes.Whenturnedcompletelytotheright(clockwise),thetimeintervalis
90minutes.Theknoballowssettingthedefrosttimeanywherebetween30and90
minutes, i.e., mid-way between the 30 and 90 minutes is 60 minutes. The Marvair®
factory set point is 30 minutes.
PLC Inputs & Outputs
The PLC has inputs located along the bottom
of the controller and outputs along the top of
the controller. An input is a signal to the PLC
from either the thermostat, sensors in the
Scholar III™ heat pump or air conditioner,
or a customer supplied input, e.g., DDC. An
output is a signal from the PLC to the heat
pump, air conditioner or to the thermostat.