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Technical Services Manager
Gulf Coast District
This month, I will be covering how to properly wire a 38MU/40MU for 24V operations and setting up the DIP switches.
I hate to say this, but the install manual is poorly written and many people get confused on why the unit does not operate on start up. Most of the confusion is understanding the DIP switches.
Many contractors are using this equipment with an Ecobee or similar type thermostat. The system can be configured several ways. When you wire this system for 24V, wire it like any other multi stage system using 18/8 wire. The part that trips people up is properly setting the DIP switches.
The indoor unit has 2 DIP switches that will need to be set and the outdoor has one.
The indoor DIP switch SWl-1 and SWl-4 will need to be turned on. The wiring diagram shows the correct location.
The outdoor unit has 1 DIP switch which needs to be turned on, SWl-2. Turning on the DIP switches tells the unit to look for 24V inputs instead of the communications RS-485.
Set the switches correctly and you should not have any problems making the system run on 24v.
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Company | Web Address | Description | |
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![]() | Aladdin Metal Products | www.aladdinmetalproducts.com | Curb Adapters and Roof Curbs |
![]() | Aprilaire | www.aprilaire.com | Indoor Air Quality Products |
![]() | Autani | www.autani.com | Building Automation and Controls |
![]() | Bard | www.bardhvac.com | Heat Pumps,Gas/Electric, and Wall Mounted Air Conditioners |
![]() | Bryant | www.bryant.com | Commercial, Industrial, Residential Heating & A/C Products and Controls |
![]() | Carrier | www.commercial.carrier.com | Commercial and Residential Heating & A/C Products |
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DXair | www.dxair.com | Pool dehumidification systems | |
First Company | www.firstco.com | Fan Coil Units | |
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Gree | www.greeusa.com | PTACs | |
Hayes Fluid Controls | www.haysfluidcontrols.com | Hose Kits and Control Valves | |
iAire | www.myiaire.com | Commercial Air Purification using ionization with energy savings | |
IslandAire | www.islandaire.com | PTACs, Vertical Units, Water Source Heat Pumps | |
i-Vu | www.commercial.carrier.com | Building Automation and Controls | |
Magic Aire | www.magicaire.com | Fan Coil Units | |
Micro Metl | www.micrometl.com | Roof Curbs, RTU Accessories, & ERVs | |
Modine | www.modine.com | Gas-Fired Unit Heaters, Duct, Furnaces, Hot Water Cabinet Unit Heaters, Makeup Air, and Dedicated Outdoor Air Systems | |
Network Thermostat | www.networkthermostat.com | Internet Thermostats, Wifi Themostats, Ethernet Thermostats | |
![]() | Payne | www.payne.com | Residential Heating & A/C Products |
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Warren Technology | www.warrenhvac.com | Electric Heaters | |
Wilo Pumps | www.wilo-usa.com | Pump Systems for HVAC and Water Supply and Sewage |