July 2016 Tech Challenge – Answer
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A residential split heat pump system, in the cooling mode @ 86° F. outdoor ambient, utilizing R-410A, has a customer complaint of no cooling. The system has TXV metering device’s on the indoor and outdoor coils with check valves. The symptoms at the home confirm that the compressor and indoor blower are running continually. What are the “possible causes” (note: there is only one problem intended) with the following measured conditions on this field service check sheet?
Note: Cooling Mode. Condenser = Outdoor Coil Evaporator = Indoor Coil
Field Service Check Sheet
| Compressor Discharge Temp. | 112 deg. F. |
| Condensing Press./Temp. | 295 psig / 94 deg. F. |
| Condensing Outlet Temp. | 88 deg. F. |
| Condenser Sub cooling | 6 deg. F. |
| Condenser Split | 8 deg. F. |
| Entering Feed Device Temp. | 87 deg. F. |
| Evaporator Press./Temp. | 101 psig / 32 deg. F. |
| Evaporator Outlet Temp. | 36 deg. F. |
| Evaporator Superheat | 4 deg. F. |
| Compressor Inlet Temp. | 48 deg. F. |
| Total S. H. | 40 Deg. F. |
| Ambient Temp. | 8 deg. F. |
| Room/Box Temp. | 86 deg. F |
| Compressor Volts | 240 V. |
| Compressor Amp. Draw | Low |
Answer: The problem appears to be restricted air flow over the evaporator (indoor coil) possibly caused by a dirty air filter. The low air flow is not allowing the 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 result. The amperage draw is low due to the low load.
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