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HVAC and Plumbing Distributor
Jonathon Pullen

Jonathon Pullen

Technical Services Manager
Gulf Coast Distrtict

Because I was Inverted

For this article, I will explain how to replace the main control board on a 38MARB ductless outdoor unit. The boards are inverted or upside down in most ductless outdoor units. 

The 38MARB board has a heat sink under the board that you cannot see with a refrigerant loop running through the heat sink. At first glance, it looks easy to replace, and it is; however, if you do not know about the hidden screws you could damage the refrigerant loop when trying to remove the board. 

Start by removing power to the unit and confirming with a meter. Remove the top cover and the fan side cover exposing the board, fan, and compressor section. 

 

Then remove the wires from the board (this will help when it is time to flip the board over). Next, find the pigtail for the compressor harness and disconnect.

Next, locate the wiring diagram on the board. Once located, take your finger and move it around the board feeling for round holes under the diagram. There are four screws holding the heat sink to the board and three are under the wiring diagram. It is best to insert a #2 Philips head screwdriver through the thin wiring diagram and remove the screws.

Once all four screws are removed, locate the small plastic clips on the front and back of the board and gently release with a flathead.

Simply lift straight up off the heat sink and lay it to the side where the copper and electrical are located. Finish removing the remaining wires and start the new board installation. Remember to add new heat sink paste to the heat sink. If this is not completed the new board may not last long.

Install the new board, assemble the unit, restore power, and check for normal operation.

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Commercial Parts

 CompanyWeb AddressDescription
Airzonewww.airzoneinc.comCustom and Underfloor Air Handlers
Aladdin Metal Productswww.aladdinmetalproducts.comCurb Adapters and Roof Curbs
Aprilairewww.aprilaire.comIndoor Air Quality Products
Autaniwww.autani.comBuilding Automation and Controls
Bardwww.bardhvac.comHeat Pumps,Gas/Electric, and Wall Mounted Air Conditioners
Bryantwww.bryant.comCommercial, Industrial, Residential Heating & A/C Products and Controls
Carrierwww.commercial.carrier.comCommercial and Residential Heating & A/C Products
Data Airewww.dataaire.comPrecision Air Control for Data Processing Centers
 DXairwww.dxair.comPool dehumidification systems
 First Companywww.firstco.comFan Coil Units
Global Plasma Solutionswww.gpshvac.comAir Purification and Bi-Polar Ionization
 Greewww.greeusa.comPTACs
 Hayes Fluid Controlswww.haysfluidcontrols.comHose Kits and Control Valves
 iAirewww.myiaire.comCommercial Air Purification using ionization with energy savings
 IslandAirewww.islandaire.comPTACs, Vertical Units, Water Source Heat Pumps
 i-Vuwww.commercial.carrier.comBuilding Automation and Controls
 Magic Airewww.magicaire.comFan Coil Units
 Micro Metlwww.micrometl.comRoof Curbs, RTU Accessories, & ERVs
 Modinewww.modine.comGas-Fired Unit Heaters, Duct, Furnaces, Hot Water Cabinet Unit Heaters, Makeup Air, and Dedicated Outdoor Air Systems
 Network Thermostatwww.networkthermostat.comInternet Thermostats, Wifi Themostats, Ethernet Thermostats
Paynewww.payne.comResidential Heating & A/C Products
Rawal Deviceswww.rawal.comContinuous Capacity Modulation and Dehumidification for DX Systems
Renew Airewww.renewaire.comFixed-Plate ERVs
Totalinewww.totaline.comCompressors, Parts, and Supplies
United CoolAirwww.unitedcoolair.comModular All-Indoor HVAC Systems
 Warren Technologywww.warrenhvac.comElectric Heaters
 Wilo Pumpswww.wilo-usa.comPump Systems for HVAC and Water Supply and Sewage