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Post insightOversized AC units cause more problems than undersized ones
An oversized AC short-cycles — it cools the air temperature quickly but shuts off before removing humidity. This leaves the home cold and clammy. Per ACCA Manual J, proper sizing accounts for insulation, window exposure, and local design temperatures. A unit 15-20% oversized will have higher energy bills, worse humidity control, and shorter compressor life than a correctly sized unit.
The 20-degree delta T rule reveals most HVAC problems instantly
Measure the supply air temperature and the return air temperature. The difference (delta T) should be 18-22°F in cooling mode. Below 15°F usually means low refrigerant. Above 25°F usually means low airflow (dirty filter, collapsed duct, frozen coil). This one measurement diagnoses 80% of residential AC complaints faster than any other test. Use a probe thermometer, not an infrared gun.
Closing vents in unused rooms increases duct pressure and wastes energy
Residential HVAC systems are designed for a specific static pressure. Closing vents raises duct pressure, which forces air through leaks, increases fan energy consumption, and can cause the evaporator coil to freeze. Per ASHRAE research, homes with closed vents use 5-10% MORE energy than homes with all vents open. The correct approach for zoning is a variable-speed system with zone dampers.
Mini-split lines must be vacuum-pulled for 30 minutes minimum — most installers rush this
Per EPA Section 608 and all manufacturer installation manuals, the refrigerant lines must be evacuated to 500 microns and held for 30 minutes to verify no leaks. Many DIY and budget installers skip this or only pull for 5 minutes. Residual moisture in the lines causes acid formation that destroys the compressor within 2-3 years. Always verify with a micron gauge, not just a manifold.
Clogged condensate drains cause more water damage than roof leaks in summer
The condensate drain on your AC removes 5-20 gallons of water per day in humid climates. When it clogs (algae, dust, debris), that water backs up into the drain pan and overflows — often into ceilings, walls, and floors. Pour 1 cup of distilled white vinegar into the drain access point every 3 months. Install a wet switch (float switch) as backup — it shuts the system off before overflow.
Clogged condensate drains cause most summer AC short-cycling
When an air conditioning system runs for 5 minutes then shuts off repeatedly, the most common cause is a clogged condensate drain triggering the float switch — not a refrigerant or compressor issue. The IRC Section M1411.3 requires condensate disposal systems. Maintenance: pour distilled vinegar through the cleanout tee seasonally. Avoid bleach, which can degrade PVC cement over time.