HVAC Diagnosis: It's NOT Just a Clogged Air Filter!

A routine service call for an AC that's not cooling quickly reveals a problem much deeper than a dirty filter. What started as a simple diagnosis turned into a critical lesson on the importance of airflow and static pressure.

In this video, we arrive to find the system shut down because the wet switch inside the emergency drain pan was triggered, a clear sign of a condensate drainage issue. The initial suspect was a clogged air filter from recent construction, and while the filter was part of the problem, it was only masking a larger, more serious issue.

The real culprit was a severely clogged secondary heat exchanger and a dirty evaporator coil. The proof was in the numbers. By placing static pressure probes at the high limit switch orifice and just after the filter, we measured a staggering 0.7" w.c. (inches of water column) across the heat exchanger. This dangerously high static pressure confirms a major airflow restriction.

UPDATE: See just how clogged the secondary heat exchanger was in our follow-up video short!

➡️ https://youtube.com/shorts/g1UTg2R_InY

This blockage is exactly why the system was freezing up in cooling mode. Left unaddressed, this same issue would cause the furnace to constantly overheat, trip the high limit switch, and eventually enter a hard lockout during the heating season. The only remedy is an immediate, thorough chemical wash of the evaporator coil to restore proper function as well as cleaning the secondary heat exchanger.

This is a perfect example of how what looks like a simple maintenance issue can be a symptom of a major, performance-killing problem hidden deep inside your HVAC system.
🔧 Key Takeaways:

A triggered wet switch in the emergency pan often points to restricted airflow and a frozen coil.

Construction dust is incredibly fine and can clog internal components even with a filter in place.

High static pressure is a system killer, causing issues in both heating and cooling modes.

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Видео HVAC Diagnosis: It's NOT Just a Clogged Air Filter! канала Nelson's HVAC, LLC