With the compressor off, a technician compares the pressure of an air-cooled condenser with the pressure given on the PT chart for that refrigerant and temperature. The system pressure is considerably higher than the pressure indicated on the PT chart for that refrigerant and temperature. This indicates that:

With the compressor off, a technician compares the pressure of an air-cooled condenser with the pressure given on the PT chart for that refrigerant and temperature. The system pressure is considerably higher than the pressure indicated on the PT chart for that refrigerant and temperature. This indicates that:

• A. The system has noncondensable gases in it.
• B. The refrigerant charge is low.
• C. The condenser is blocked.
• D. The compressor is faulty.

Answer: (A)

Noncondensable gases in the condenser prevent heat from being rejected efficiently, so the system can’t condense the refrigerant at the expected rate. The PT chart shows the expected high-side (condensing) pressure for a clean condenser and proper charge at a given temperature. If the measured condenser pressure is significantly higher than that chart value, it means something is hindering heat transfer, with noncondensables being the classic cause. The noncondensables take up space and form an insulating layer, raising the head pressure even though the temperature environment is the same. A low charge would not typically push the pressure higher than the chart; a blocked condenser could, but the diagnostic cue most consistent with the higher-than-expected pressure in this scenario is the presence of noncondensable gases. A faulty compressor would be evaluated when the unit runs, not just from a static off condition.

Noncondensable gases in the condenser prevent heat from being rejected efficiently, so the system can’t condense the refrigerant at the expected rate. The PT chart shows the expected high-side (condensing) pressure for a clean condenser and proper charge at a given temperature. If the measured condenser pressure is significantly higher than that chart value, it means something is hindering heat transfer, with noncondensables being the classic cause. The noncondensables take up space and form an insulating layer, raising the head pressure even though the temperature environment is the same. A low charge would not typically push the pressure higher than the chart; a blocked condenser could, but the diagnostic cue most consistent with the higher-than-expected pressure in this scenario is the presence of noncondensable gases. A faulty compressor would be evaluated when the unit runs, not just from a static off condition.