Heating, ventilation, and air conditioning (HVAC) systems can be complex and mysterious to homeowners. So when there’s an issue, finding the cause is often way beyond the DIYer’s scope. When a Miami homeowner was tired of living with temperature imbalances throughout his home, he called the team at Ask This Old House for help, and building engineer Ross Trethewey showed up to help.
How Experts Troubleshoot an AC System
- Determine the Load
If the HVAC system isn’t operating correctly, a load calculation needs to be performed to determine how much heating and cooling the home needs. This can typically be done with the home’s plans, but if they’re not available, a measurement of each room’s volume needs to be taken. This includes checking the ceilings, windows, walls, doors, and registers, as well as the insulation in the walls and ceilings. - Preliminary HVAC System and Exterior Inspection
Next is an HVAC system inspection. The goal here is to locate the air handler and condenser unit rating plates to determine if the system is sized correctly for the home, using the load calculation performed earlier. A pro will also look for roof ventilation and standard vents to get a better idea of the home’s layout and functions. - Perform a Leakage Test
A pro will close all of the exterior openings (windows, doors, and vents), shut off any HVAC or combustion systems, and install a blower door. The blower door depressurizes the home and allows the technician to test each space for leakage. The readings provided during these tests will help the technician determine how much outdoor air is pulled into the living space. - Measure Supply Air Volume
To determine the amount of supply air coming from the supply registers, the technician will use a tool called a “flow hood” to measure the amount of air being supplied to each room, both with their interior doors opened and closed. These measurements are taken in each room to find balancing issues. - Test Static Pressure
Testing the actual air handling unit is important as well. To do this, the technician will install a meter in the unit to measure the airflow at the air handler. - Smoke Test
Finally, a smoke test is performed. Theatrical smoke is introduced into the HVAC system. The duct system is then observed, helping the technician pinpoint the location of any leaks. - Testing and Inspection Findings
After the entire test and inspection process is complete, the findings are reported to the homeowner. The technician will typically suggest solutions at this point, as well.
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Assistance provided by: Comfort Dynamic, Inc.
