38MU/40MU Crossover System

249 VAN Launch Kit 249 VAN Consumer Brochure Smart Thermostat Sell Sheet 249 VAN Launch Kit

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This installation was on a 4-story home, and the tech had not yet gone to the basement to troubleshoot the “infinity” water source heat pump, as he was told he by the homeowner. He was in the attic at the infinity furnace above the 4th floor. He was getting his dcv in the proper range on his A and B green plug on the air handler, 3 to 4 vdc. His indoor board ohm reading was in range, 28k to 32 k. The tech ohmed out the A and B thermostat wires on the water source heat pump from the upstairs. His ohm reading was not in range of a normal infinity board. His reading was around 64.4k. The tech then made the long walk to the basement where the “geothermal heat pump” was located. Bingo.

In this article, I will explain how to wire the new crossover system for 24V communication or scenario 3 using a 3rd party thermostat.

There seems to be some confusion when wiring this system for scenario 3. Wire the system like any other multistage system. Wire the system for 3 heat 2 cool if you are using heat strips. The most important part of scenario 3 is setting the dip switches in the units.

First, set dip switch SW1 on the indoor unit. Also, SW1-1 and SW1-4 needs to be turned ON. This tells the indoor unit to look for 24V inputs like any other system.

Disclaimer: The technical statements, information and recommendations contained herein are believed to be accurate as of the date hereof, but Mingledorff’s does not make representations or warranties, express or implied, as to its accuracy, its completeness, or the results to be obtained. The information is being provided for informational purposes only and is intended for use by persons having adequate skill and expertise regarding the proper selection, use and application of the products and recommendations and at their own risk and discretion.

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