May 2017 Tech Challenge Answer - IE3: Business Tools for HVAC & Plumbing Contractors  

May 2017 Tech Challenge Answer

A commercial rooftop utilizing R-410A with a TXV feed device (and receiver) has a customer complaint of “insufficient cooling.” The symptoms confirm inadequate cooling and the compressor appears to be running all of the time and the thermostat is not satisfied. What are the “possible causes” (Note: There is only one problem intended) with the following measured conditions on this field service check sheet?

Field Service Check Sheet

Compressor Discharge Temp. 236 deg. F.
Condensing Press./Temp. 442 psig / 124 deg. F.
Condensing Outlet  112 deg. F.
Condenser Sub cooling 12 deg. F.
Condenser Split 36 deg. F.
Entering Feed Device Temp. 89 deg. F.
Evaporator Press./Temp. 125 psig / 43 deg. F.
Evaporator Outlet Temp. 52 deg. F.
Evaporator Superheat 11 deg. F.
Compressor Inlet Temp. 68 deg. F.
Total S. H.  25 deg. F.
Ambient Temp. 88 deg. F.
Room/Box Temp. 78 deg. F
Compressor Volts 240 V.
Compressor Amp. Draw  High

And The Answer is…

The problem appears to be a restricted air flow over the condenser caused from a dirty condenser, diverted air flow or condenser fan issue. The condensing pressure/temperature, and condenser split are high to expel the heat gained in the evaporator, superheat and compressor. The high compression ratio is causing recompression, high discharge temperatures and high amperage. The subcooling and superheat are high to normal because the TXV is attempting to maintain a constant S.H. with a lower refrigerant flow caused by the higher compression ratio.

Melissa Broadus

Editor at IE3
Melissa Broadus is editor of IE3 Magazine and its associated websites. She also serves as Director of Communications for ACCA.

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