Many homeowners believe things about their AC that just aren’t true – and those myths can cost you money and comfort. Let’s clear things up!
“Bigger units cool better.”
Actually, oversized ACs short cycle, wasting energy and wearing out faster. Proper sizing is key for efficient cooling.
“Change filters only when they look dirty.”
Your AC’s airflow drops long before you see dirt. Changing filters every month keeps your system healthy and efficient.
“Turning the thermostat way down cools the home faster.”
Your AC runs at a fixed speed no matter the setting, so setting it lower just makes it run longer.
“Closing vents in unused rooms saves energy.”
Closing vents disrupts airflow, creating pressure problems that strain your system.
“If it’s working, skip maintenance.” Routine maintenance catches issues early and extends your system’s life, saving you from costly repairs.
Key takeaways
- Removing moisture takes run time, so anything that shortens run time costs comfort and money.
- No thermostat setting changes how fast equipment removes heat, only how long it runs.
- A fan makes people feel cooler without removing heat, so one in an empty room is waste.
- Refrigerant is not a consumable, so a system that wants charge every summer is leaking.
Why does extra capacity leave a house cool and damp?
Water leaves the air only once the indoor coil has been running long enough to be thoroughly wet. Too much capacity reaches the setpoint before that, so the temperature drops and the moisture stays. Test it on a 90 degree afternoon: right-sized cooling runs in long stretches, not eight minute bursts. Our guide to sizing the equipment properly covers the load calculation.
Why change a filter that still looks clean?
Pleated media loads through its depth, not just at the surface, so resistance climbs well before a filter looks dirty. The blower answers by moving less air over the coil, which stretches cycles and can frost it. Replace on a schedule and write the install date on the frame. Intervals are in our guide to how often to service a system.
Does setting the thermostat to 65 cool the house faster?
No. A single stage compressor has one capacity, so it removes the same heat per hour at 65 as at 74. The lower number changes only how long it runs. Variable speed equipment modulates, but never above its rating. A house that never reaches its setpoint has a capacity, airflow, or charge problem, not a thermostat problem. The setpoint guide has the numbers.
Does shutting a spare room’s register save anything?
Closing registers does not lighten the blower’s job; it raises static pressure in the ducts, and that pressure forces more air out through seams and joints. Where ducts cross an attic or crawl space, that air is lost outdoors. The closed room still trades heat through its walls, so you never stop paying for it. Balancing, zoning, and duct pressure testing are the real fixes.
Why does a system that seems fine need maintenance?
Because performance drifts rather than fails. A tune-up is measurement: motor current against the nameplate, static pressure across filter and coil, and the drop from return air to supply air, which commonly sits near 16 to 22 degrees and runs lower in humid weather. Numbers outside those bands flag what kills compressors; see what shortens equipment life and Shemtov Systems service agreements.
Do ceiling fans actually cool a room?
No. A fan removes no heat from a room; the electricity its motor uses ends up there as heat. It moves air across skin so perspiration evaporates faster, which is the cooling you feel. Used well it lets you sit at a higher setting, so the compressor runs less. Check the reversing switch too: in summer the blades should push air down.
Is a higher MERV filter always better?
Not always. MERV scores how much of the 0.3 to 10 micron range a filter captures, on a scale of 1 to 16, so a higher number catches finer particles. EPA puts the target at MERV 13. The ceiling is what your equipment can breathe through: whistling at the return, weak airflow, or a filter bowed inward means it is too restrictive.
Does an AC need refrigerant topped up every year?
No. Refrigerant is not consumed; it circulates and returns. A system that wants charge every summer is leaking, and adding a pound a year is not a repair. A proper fix means finding the leak with a detector or a nitrogen pressure test, sealing it, pulling a vacuum, then weighing in the nameplate charge. See air conditioning service in Silver Spring.
Frequently asked questions
My air conditioner is icing over. Can I keep running it?
No. Switch cooling off, run the fan until the ice melts, then look for a loaded filter, closed registers, or low charge. An iced coil sends liquid refrigerant back to the compressor.
Does shading or covering the outdoor unit help it work better?
Very little, and only if the shade never blocks airflow. The condenser pulls air through every side of its cabinet and discharges upward, so keep it clear and never run it covered.
Can I buy refrigerant and top up my own system?
No. Since January 1, 2018 the EPA sales restriction has covered refrigerants such as R-410A, which may be sold only to a Section 608 certified technician or an employer of one.
If one of these myths shaped how you run your system, measurement beats opinion. Shemtov Systems has worked out of Silver Spring since 1981, with NATE-certified technicians, licensed and insured in Maryland and Washington DC, and a 24-hour answering service on 240-355-3333.