Mitsubishi Electric PAA-A18AA1 User manual

MANUFACTURED FOR:
MITSUBISHI ELECTRIC US, INC.
Air Conditioners
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
SERVICE MANUAL

Table of Contents
1. SAFETY PRECAUTIONS ........................................................................................................ 3
1.1. Before service and electric work .................................................................................... 3
1.2. Devices that use R410A refrigerant .............................................................................. 10
1.3. Before getting started .................................................................................................. 11
1.4. Before servicing or moving the PAA unit - electrical work ............................................... 16
1.5. Before starting the test run ........................................................................................... 18
1.6. To dispose of the PAA unit ........................................................................................... 19
2. INSTALLATION POSITIONS AND CORRESPONDING AIRFLOW DIRECTION ........................ 20
3. SPECIFICATIONS ................................................................................................................. 21
4. INTERNAL PRESSURE DROP ............................................................................................... 22
5. OUTLINES AND DIMENSIONS .............................................................................................. 25
6. WIRING DIAGRAM ................................................................................................................ 28
7. REFRIGERANT SYSTEM DIAGRAM ...................................................................................... 30
8. TEST MODE AND EMERGENCY MODE ................................................................................ 31
9. HUMIDIFIER CONTROL SPECIFICATIONS ............................................................................ 36
9.1. Humidifier ................................................................................................................... 36
9.2. Installation .................................................................................................................. 38
10. ERV (ENERGY RECOVERY VENTILATION) CONTROL ........................................................ 39
10.1. Energy recovery ventilation (ERV) .............................................................................. 39
10.2. Installation ................................................................................................................ 40
10.3. HRV/ERV heating operation for MXZ system ............................................................... 40
11. TROUBLESHOOTING .......................................................................................................... 41
11.1. Cautions on troubleshooting ....................................................................................... 41
11.2. Self-check function, Function Table ............................................................................. 42
11.3. Self-diagnosis action table .......................................................................................... 44
11.4. Troubleshooting by inferior phenomena ....................................................................... 49
11.5. Test point diagram ..................................................................................................... 50
11.5.1. Power supply board ........................................................................................ 50
11.5.2. Indoor controller board .................................................................................... 51
11.6. Trouble criterion of main parts .................................................................................... 52
11.7. Thermistor ................................................................................................................. 53
12. FUNCTIONS OF DIP SWITCH AND JUMPER WIRE ............................................................. 54
13. DISASSEMBLY PROCEDURE .............................................................................................. 55
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 2 © 2022 Mitsubishi Electric US, Inc.

1. SAFETY PRECAUTIONS
• Before servicing the unit, make sure you read all the safety precautions.
• Ensure all the equipment is properly installed per the installation manual.
• Ensure all precautions are followed.
• Carefully read the labels affixed to the main unit.
Symbols used in text:
WARNING
Describes precautions that should be observed to prevent the danger of injury or death to
the user.
CAUTION
Describes precautions that should be observed to prevent damage to the unit.
1.1. Before service and electric work
IMPORTANT
The Environmental Protection Agency of the United States (EPA) and Canadian Provincial
environmental agencies have issued various regulations regarding the introduction and
disposal of refrigerants. Failure to follow these regulations may harm the environment and
can lead to the imposition of substantial fines.
NOTE
The service of the unit is regulated by the mechanical code adopted by the authority
having jurisdiction.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 3 © 2022 Mitsubishi Electric US, Inc.

WARNING
Risks related to PAA unit servicing
• PAA unit must be serviced by a dealer, contractor, or technician with certifications
required by laws and codes.
– Improper service by the user may result in injury or damage to the unit such as water
leakage, electric shock, or fire.
• Be sure the unit is installed in a place that can withstand its weight before servicing.
– Inadequate strength may cause the unit to fall, resulting in injuries.
• In order to prevent the PAA unit from falling during typhoons, hurricanes, earthquakes
etc., be sure the unit is properly secured.
– Improper service may cause the unit to topple and result in injury.
• Prohibit anyone without the proper qualifications from doing repairs. If the air conditioner
must be repaired, consult a dealer, contractor or technician with certifications required by
laws and codes.
– If the PAA unit is repaired improperly, water leakage, electric shock, or fire may result.
• Service the air conditioner according to this service manual.
– If the unit is serviced improperly, water leakage, electric shock, or fire may result.
• Ensure the outdoor unit cover panel is installed correctly. Please refer to the outdoor
unit’s manual for proper installation.
– If the terminal cover panel is not installed correctly, dust or water may enter the
outdoor unit, which could result in fire or electric shock to the user.
• Ensure that the stop valves are opened immediately after connecting, vacuuming and
pressure testing the refrigerant lines when connecting the PAA unit to the outdoor unit.
– Failure to due so may cause the PAA unit or refrigerant lines to rupture because of
high-pressure refrigerant during the furnace's heating operation.
• If the PAA unit is not installed according to the installation manual, which requires a float
switch, condensed water from the PAA heat exchanger will deviate from the specified
path and may cause water to leak on to the heat exchanger of the gas furnace. This
may cause gas, oil, and water leakage from the furnace due to corrosion over time.
Furthermore, this can lead to poisoning, fire, explosion, water leakage, and bodily harm
and damage to property.
• When PAA unit (this product) is supported from the ceiling in a garage or an occupied
area, the product may fall due to insufficient strength of the suspension or support,
or deterioration over time, etc., causing bodily harm and damage to property. In some
cases, it can lead to death. Properly support the PAA unit in these situations.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 4 © 2022 Mitsubishi Electric US, Inc.

WARNING
Electrical risks
• When sizing wire and completing electrical connections during installation, please follow
local codes and standards.
– Inadequate connections and fastening may generate heat and cause a fire.
• Have all electric work performed by a properly qualified electrician in the state where the
electric work is being performed, according to the “National Electrical Code" and local
electrical codes, “Interior Wire Regulations” and the instructions provided in this service
manual, and always use a dedicated circuit.
– If the power source capacity is inadequate or electric work is performed improperly,
electric shock or fire may result.
• Keep the electric parts away from water.
– It might result in electric shock, fire, or smoke.
• Do not reconstruct or change the settings of the protection devices.
– If the pressure switch, thermal switch, float switch or other protection devices are
shorted and operated forcibly, or parts other than those specified by Mitsubishi Electric
are used, fire or explosion may result.
• If the supply cord is damaged, it must be replaced by the manufacturer service
personnel or licensed person.
• Be sure to ground the outdoor unit in accordance with local code. Do not connect the
earth cable to any gas pipe, water pipe, lightning rod, or telephone earth cable.
WARNING
Refrigerant leak risks
• If refrigerant gas leaks during service work, ventilate the room and do not use the
furnace until a technician considers that it is safe to use the furnace.
– If the refrigerant gas comes into contact with a flame, poisonous gases will be
released. When the odor is detected, contact a dealer, contractor or technician
regarding the appropriate measures to prevent the safety limit from being exceeded.
• After completing service work, make sure that refrigerant gas is not leaking.
– If the refrigerant gas leaks and is exposed to a fan heater, stove, oven, or another
heat source, it may generate noxious gases.
• Do not use refrigerant other than R410A.
– Doing so may cause the unit or pipes to burst, or result in an explosion during use,
repair, or at the time of disposal of the unit.
– Doing so may also be in violation of applicable laws.
– The manufacturer, Mitsubishi Electric Corporation, its affiliates and suppliers, cannot
be held responsible for malfunctions or accidents resulting from the wrong type of
refrigerant used.
• When the outdoor unit service valve is left closed after installation/service, or when
the outdoor unit service valve is closed due to operation stop, the volume of the
liquid refrigerant in the A-Coil and refrigerant piping will expand due to the the heating
operation in the gas furnace. This may cause the A-Coil or refrigerant piping to rupture.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 5 © 2022 Mitsubishi Electric US, Inc.

WARNING
Fuel leak risks
• Fuel and combustion gas may flow into the room if the exhaust duct is leaking, there
is a gap due to insufficient fixing of the connection part, or if regular maintenance is
neglected. As a result, fatal hazards such as poisoning and fire explosion may occur, so
regular maintenance is recommended to check for the following:
– Cracked ducts
– Clogged ducts
– Insufficient exhaust capacity or abnormal stop of the exhaust fan of gas furnace
– Gas leak due to gas furnace heat exchanger failure (including corrosion due to poor
installation environment)
– Incomplete combustion due to gas furnace equipment failure (malfunction / parts *
failure)
* Parts refer to piping, valves, electrical wiring, electrical / electronic parts, sensors,
circuit breakers, etc.
– Short-circuit or ground fault due to ignition, tracking or insufficient insulation of gas
furnace parts
– Damage to internal and external wiring of gas furnace
– Deterioration of heat resistance, strength, corrosion resistance, insulation, etc. of gas
furnace peripheral components
– Gas furnace protection circuit malfunction
– Electrical components for electromagnetic noise interference due to normal use over
time, parts failure, and/or installation of nearby electrical devices
– Inadequate confirmation of recalled products from the design / manufacturing year of
gas furnace
– Maintaining an abnormal installation state by overlooking a gas furnace installation
error or a red tag
• If our equipment is not installed, used, serviced, or maintained as described in the
PAA unit installation/operation/service manual, the following problems may occur. In this
case, stop the operation immediately by turning off the power, etc., and ask the dealer or
contractor for an inspection. Otherwise, gas leaks can cause poisoning, fire, explosions,
water leaks, etc., which can cause serious bodily harm and damage to property.
– If the installation or operating environment is out of the warranty range, the control box
may malfunction, and the gas furnace protection functions may also fail and disable.
The effect of the excessive heat generated by the gas furnace can cause cracks in
the A-Coil section resulting in refrigerant and oil leaks. Furthermore, poisoning, fire,
and explosions may occur from this, doing so can cause bodily harm and damage to
property.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 6 © 2022 Mitsubishi Electric US, Inc.

WARNING
Safety guidelines
• Follow all safety codes specified in the region where the service work is to take place.
Wear appropriate protective equipment such as safety glasses, protective clothing, and
gloves during service work such as refrigerant filling, torque wrench use, and unit
transportation. Use a quenching cloth and have a fire extinguisher available during
brazing operations.
– Failure to follow safety requirements can result in injury or death or building damage.
• Do not touch the heat exchanger fins.
– Improper handling may result in injury.
• Never substitute parts or components from other manufacturers when repairing or
replacing components in the PAA unit. Never service or operate the PAA unit if any
parts or components are damaged.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 7 © 2022 Mitsubishi Electric US, Inc.

WARNING
Service guidelines
• Read this manual carefully and follow all warnings and cautions provided with this unit.
Refer to your local building code and the latest National Electrical Code (NEC) NFPA70.
In Canada, be sure to refer to the latest Canadian Electrical Code CSA C22.1. Also,
follow all codes specified by your region.
We recommend installing a CO sensor and ventilation system.
– Failure to follow safety requirements can result in injury, death or building damage.
• When moving and reinstalling the PAA unit, consult the dealer, contractor or technician
with certifications required by laws and codes.
– If the air conditioner is serviced improperly, water leakage, electric shock, or fire may
result.
• Ask a dealer, contractor or technician with certifications as required by laws and codes
to service the accessories.
– Improper service by the user may result in water leakage, electric shock, or fire.
• Pay attention to the unit service location. Refrigerant is heavier than air and locations
such as basements or crawl spaces where refrigerant can accumulate can become
dangerous.
– Inadequate ventilation can lead to poisoning.
• The appliance is not intended for use by persons with reduced physical, sensory or
mental capabilities, or lack of experience and knowledge (including children) unless they
have been given supervision or instruction concerning the use of the appliance by a
person responsible for their safety.
•Do not add UV Lights into the PAA unit cabinet or to the attached ductwork.
•–UV Lights can cause degradation to plastic and insulation parts. Water leakage,
electric shock, or fire may result.
• If the gas furnace is not certified to safety standards (ANSI Z21.47/CSA2.3) by a
nationally recognized third-party certification organization (AGA, UL, CSA, ETL/Intertek,
etc.), or if the gas furnace does not comply with ACCA (Air Conditioning Contractors
Association) Standards and Guidelines (Code), NFPA54 (National Fuel Gas Code),
NFPA70 (NEC: National Electrical Code), and if the equipment is not properly installed,
used, serviced, and maintained in accordance with the building code for each district
(state, county, city, town, etc.), the following hazards may occur even if our equipment is
properly designed, installed, and operated, and serviced.
– If a leak sensor is not installed in the room, there is a risk of poisoning symptoms and
death without noticing a toxic gas leak.
– Gas fuel has an odor, but if you do not notice it, there is a risk that it can cause
poisoning symptoms or an accident, such as a fire or explosion.
– If the safety of gas furnace, gas supply piping, and exhaust duct worsen due to
improper ventilation of the system [ventilation must be in accordance with Law,
Standard or Guideline (Code)], or due to aging deterioration or the influence of the
usage environment, there is a risk of poisoning symptoms due to combustion gas or
igniting fuel gas and causing a fire or explosion.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 8 © 2022 Mitsubishi Electric US, Inc.

CAUTION
Risks related to PAA unit servicing
• When servicing and relocating the PAA unit, do not charge it with a refrigerant different
from the refrigerant specified on the unit.
– If a different refrigerant or air is mixed with the original refrigerant, the refrigerant cycle
may malfunction and the unit may be damaged. Use only recommended refrigerant
specified in ODU manual for system operation (ONLY R410A).
• The PAA unit is designed for indoor installation only.
• The PAA unit must be installed downstream (discharge air) side of the furnace.
• Do not alter the cabinet or braze inside the cabinet. Quench all brazed joints with water
or a wet rag to avoid overheating after brazing.
– It may affect the performance of the PAA unit.
• Do not use leak detection additive.
– ODU and PAA unit parts may be damaged by the refrigerant/additive mixture.
Refrigerant leak risks
• The service (technician) shall ensure there is no refrigerant leakage according to local
regulations and standards.
– Refrigerant leakage will affect the performance of the heat pump.
Service guidelines
• For PAA unit piping connections, use flare connection as the equipment was designed
for. Mitsubishi Electric US, Inc. is not responsible for improper brazing connection done
by the service technician.
– For pipe flaring, use an R410A flaring tool.
– Improper brazing connections may cause damage to the PAA unit.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 9 © 2022 Mitsubishi Electric US, Inc.

1.2. Devices that use R410A refrigerant
CAUTION
Service guidelines
• Use refrigerant piping made of C12200 (Cu-DHP) phosphorus deoxidized copper as
specified in the ASTM B280 Standard Specification for Seamless Copper Tube for Air
Conditioning and Refrigeration Field Service. Ensure that the inner and outer surfaces of
the pipes are clean and free of hazardous Sulphur, oxides, dust/dirt, shaving particles,
oils, moisture or any other contaminants.
– Contaminants on the inside of the refrigerant piping may cause the refrigerant residual
oil to deteriorate.
• Store the piping to be used during service indoors and keep both ends of the piping
sealed until just before brazing. (Store elbows and other joints in a plastic bag.)
– If dust, dirt, or water enters the refrigerant cycle, deterioration of the oil will result in
malfunction of the compressor.
• Do not use a refrigerant other than R410A.
– If any other refrigerant is used, the chlorine in that refrigerant may cause the
refrigerant oil to deteriorate.
– Since R410A does not contain any chlorine, gas leak detectors for conventional
refrigerant will not react to it.
• Use a vacuum pump with a reverse flow check valve.
– The vacuum pump oil may flow back into the refrigerant cycle and cause the
refrigerator oil to deteriorate.
• Do not use the following tools that are used with refrigerants other than R410A:
– Gauge manifold, charge hose, gas leak detector, reverse flow check valve, refrigerant
charge base, vacuum gauge, refrigerant recovery equipment.
• Do not use a charging cylinder.
– It may cause the refrigerant to deteriorate.
• Use liquid refrigerant to fill the system.
– If gas refrigerant is used to seal the system, the composition of the refrigerant in the
cylinder will change and performance may drop.
PAA-A18, 24, 30, 36, 42AA1/BA1/CA1
Specifications are subject to change without notice. 10 © 2022 Mitsubishi Electric US, Inc.