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Tong Ngo

Technical Service Manager • North Georgia

Ductless Commission/Testing In Heat Mode

Have you ever installed a mini split in the summertime? During the commission the AC would work well, but in heat mode unit will not run at all. To know the reason why the unit will not run in heat mode, we must know what each T’s sensor does.

  • T1: Indoor room temperature
  • T2: Coil temperature of indoor heat exchanger middle
  • T2B: Coil temperature of indoor heat exchanger outlet
  • T3: Coil temperature of condenser
  • T4: Outdoor ambient temperature
  • T5: Compressor discharge temperature
  • Td: Target temperature
  • Ts: Set Point Temperature

In this situation, we know the unit works well in cool mode.  In heat mode, the unit will not run at all.  In heating operating range, the unit will not heat if the outdoor temperature exceed 86 degree. 

The day the tech tried to commission this unit.  The outdoor temperature was over 90 degrees.  The unit was on a black roof and in direct sunlight.

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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