July Tech Challenge ANSWER

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A commercial split heat pump system in the cooling mode @ 88° F outdoor ambient, utilizing R-410A, has a customer complaint of no cooling. The system has TXV metering devices on the indoor and outdoor coils with check valves. The symptoms at the business confirm that the compressor and indoor blower are running continuously. What are the “possible causes” with the following measured conditions on this field service check sheet? Note that in the cooling mode, the condenser is the outdoor coil, and the evaporator is the indoor coil.

Note: There is only one problem intended.

Field Service Check Sheet 

• Compressor Discharge Temp. 109° F. 
• Condensing Press./Temp. 295 psig / 94° F. 
• Condensing Outlet Temp. 90° F. 
• Condenser Sub cooling 4° F. 
• Condenser Split 6° F. 
• Entering Feed Device Temp. 88° F. 
• Evaporator Press./Temp. 101 psig / 32° F. 
• Evaporator Outlet Temp. 36° F. 
• Evaporator Superheat 4° F. 
• Evaporator Split 48° F.  
• Compressor Inlet Temp. 48° F. 
• Total S. H. 16° F. 
• Ambient Temp. (Outdoor) 88° F. 
• Room Temp. (Indoor) 80° F. 
• Compressor Volts 240 V. 
• Compressor Amp. Draw low 

 

ANSWER:

The problem appears to be restricted airflow over the evaporator (indoor coil), possibly caused by a dirty air filter or obstruction. The low airflow is not allowing the building heat load to be absorbed in the refrigerant, so the pressures and splits are low, as well as the S.C. and S.H. The refrigerant entering the compressor is barely above saturation and compressor flooding resulting in compressor failure could possibly result. The amperage draw is low due to the low load. 

Cheers.

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Posted In: Tech Challenge