Why Your North Las Vegas AC Runs But Won’t Cool Below 80 Degrees

It is July in North Las Vegas. The thermometer outside reads 112. Your AC has been running for six hours straight and the house is still 81 degrees. The unit is on, it’s blowing air, but it cannot seem to pull the temperature down. This is one of the most common HVAC complaints we get across the Las Vegas Valley, and it has several distinct causes, only some of which require a refrigerant charge.

The Most Common Causes, in Order of Frequency

The most frequent cause we find is dirty evaporator or condenser coils. The evaporator coil (inside the air handler) absorbs heat from the return air. The condenser coil (in the outdoor unit) rejects that heat outside. Both are heat transfer surfaces. When they are coated in dust, pet dander, and debris, heat transfer efficiency drops. The unit runs but cannot move heat fast enough to overcome the load. In North Las Vegas, condenser coils in new construction areas also accumulate desert particulate and construction dust faster than in established neighborhoods.

The second most common cause is low refrigerant from a slow leak. A system does not consume refrigerant. If refrigerant is low, there is a leak somewhere. Low refrigerant reduces the system’s capacity to absorb heat. The symptoms are a unit that runs constantly, suction line that is not cold to the touch or is icing over, and a house that stays 5 to 10 degrees above setpoint on hot days even though the system seems to be running normally.

The third cause, which most homeowners do not consider, is an undersized system or an incorrectly designed duct system. North Las Vegas has seen rapid residential construction growth. Some homes in newer developments were sized from load calculations that used optimistic assumptions about insulation, infiltration, and window efficiency. An undersized system for the actual heat load of the home will never cool the house to setpoint on a 112-degree afternoon regardless of its condition.

What Happens When the Outdoor Temperature Exceeds the System’s Design Day

Most residential HVAC systems in the Las Vegas Valley are sized to maintain a 75-degree indoor temperature when outdoor temperature is 105 to 110 degrees. On days that exceed the design temperature, the system loses the capacity to keep up. A system that holds 75 at 108 degrees may only hold 79 or 80 at 113. This is not a malfunction. It is physics. On the hottest days of the year, any system that was correctly sized for design day will be running at or near its capacity limit.

If your system cannot hold temperature on days below the design temperature, or if it loses capacity to cool at all, that is worth investigating. Call (702) 840-5163 or visit our contact page. See our gallery.

What a Diagnostic Visit Covers

When we arrive for an AC diagnostic in North Las Vegas, we measure refrigerant pressures, calculate superheat and subcooling to confirm charge, check condenser and evaporator coil condition, measure system static pressure, check supply airflow CFM, and verify compressor amp draw. This takes 45 to 90 minutes. The findings determine whether the problem is refrigerant, coil cleanliness, airflow, equipment condition, or load versus capacity mismatch. We explain what we found and quote the repair before doing anything. No surprises.