HVAC Repair Desk
117 plain-English guides, written for homeowners

Too hot? Too cold? Let's figure out why.

Pick what your system is doing. We walk you through the safe checks first, then explain what a fix should cost if you need a pro.

Find my problemBrowse all guides
A smart thermostat with a glowing ring on a living room wall, with a sofa and window behind it
68°Set to 72°, running for 2 hours.
Why is it not catching up?

What's happening right now?

Start with the symptom, not the jargon.

Four checks before you call anyone

Plenty of service calls end with a reset breaker or a new filter. These take five minutes and need no tools.

  1. Check the thermostatSet it to Cool or Heat and a few degrees past the room. A blank screen usually means dead batteries.
  2. Check the breakerA tripped breaker stops the outdoor unit or the furnace cold. Reset it once. If it trips again, leave it off.
  3. Check the filterA filter clogged solid chokes airflow. Hold it to the light and replace it if you cannot see through it.
  4. Look for ice or waterFrost on the copper line or water around the indoor unit points to an airflow or drain problem.

Browse by topic

An outdoor air conditioner with its service panel removed and hand tools laid out on the grassRepairs35 guidesSymptom-first guides to capacitors, compressors, flame sensors and more.A new outdoor heat pump on a concrete pad beside a modern wood-sided homeInstallation & Replacement63 guidesSizing, efficiency, brands and real install costs before you sign.Hands sliding a clean pleated air filter into a furnace, with the old dusty filter beside itMaintenance & Service13 guidesFilters, coils and tune-ups: the cheap habits that prevent breakdowns.
A bright room with sheer curtains moving in the airflow and potted plants by the windowIndoor air qualityHumidifiers, purifiers, UV lights and duct sealing. 5 guidesA thermostat glowing orange in a dark hallway on a hot summer nightEmergency HVACNo cooling in a heat wave, no heat in a freeze: the first hour.

Know the price before the quote.

Cost factors, typical ranges from published sources, and the questions that make a contractor's quote easy to read.

A clipboard with an estimate, a pen and a calculator resting on a new outdoor AC unit

Fresh guides

All 117 guides by topic
Close-up of frosted copper refrigerant lines on an air conditioner evaporator coilRepairs · 8 minAC Freezing Up: Causes of a Frozen AC Unit and How to Fix ItA white PVC condensate drain line and a small condensate pump beside an indoor air handlerRepairs · 11 minAC Refrigerant Leak: Signs, How Leaks Are Found, and AC Recharge CostA clipboard with an estimate, a pen and a calculator resting on a new outdoor AC unitCost guide · 9 minAC Replacement Cost: Typical Prices, Cost Factors and How to Read a QuoteA dual run capacitor and a contactor wired inside an outdoor AC electrical panelRepairs · 8 minAC Short Cycling: Why Your AC Turns On and Off Frequently

Questions we hear most

Why is my AC freezing up?

An AC freezes when the indoor evaporator coil drops below 32 degrees F and the moisture it pulls from the air turns to ice. The two main causes are not enough warm air moving across the coil, from a dirty filter, closed vents, a dirty coil or a weak blower, and low refrigerant from a leak. Running the AC when it's cool outside can also do it.

How much does it cost to replace a central air conditioner?

Most published cost guides put a central AC replacement with existing, usable ductwork somewhere around $4,000 to $8,000 installed, with reported national averages close to $6,000. Higher-efficiency variable-speed systems, new ductwork, electrical upgrades or a hard install can push the total past $12,000.

How much does an AC tune-up cost?

Most national cost guides put a standard central AC tune-up at roughly $70 to $200, with reported averages around $130. Ductless and multi-zone systems, hard-to-reach equipment and peak-season bookings tend to cost more. Repairs, parts and refrigerant are billed on top.

Do I need a dehumidifier in my crawl space?

You need one if the crawl space is sealed and still reads above 60 percent in humid weather. In a vented crawl space over open dirt, fix the ground and vents first, or the dehumidifier just dries outdoor air.

What qualifies as an AC emergency?

A burning or electrical smell, smoke, sparking, a breaker that trips again after one reset, water coming through a ceiling, or no cooling when someone in the home is at high risk from heat. A system that is cooling poorly or making a new noise can usually wait for a daytime appointment if you switch it off.