How to test the AC and heat before you need them
Test AC and heat soon after you move in, so you find problems before you need them. Run the heat in any weather. Hold off on the AC unless it's warmer than about 60°F outside, because cooling in colder weather can damage the compressor. Check each room, the drain line and the shutoff, and report problems in writing.
How to test AC and heat and what a good run looks like
A system that turns on hasn't passed yet. ENERGY STAR's maintenance list has technicians confirm that a system starts, runs and shuts off properly, so copy that. You want a clean full cycle, air moving at every register, and water leaving through the condensate drain when the AC or a heat pump runs in cooling mode.
There's one real limit on the "any season" idea. The American Home Inspectors Training Institute says not to run an air conditioner, or a heat pump in cooling mode, when it's below about 60°F outside. Refrigerant can condense into a liquid in the compressor, and liquid can damage parts built to compress gas. The exact cutoff varies by maker, so check your unit's manual.
In cold weather, test the heat now and put the AC on your calendar for the first warm stretch. You can still look the outdoor unit over without turning it on. A furnace has no such limit, so you can run it on a hot day. It only needs a short run. If you have a heat pump, check its manual first.
How to test AC and heat, step by step
- Check the outdoor temperature
If it's below about 60°F, or below the limit in your manual, test heat only and save the AC for later.
- Look at the filter
A clogged filter can make a good system seem bad. Replace it first so the test is fair.
- Run the heat
Set the thermostat a few degrees above room temperature and let it run for 15 minutes. Walk each room and feel the registers.
- Run the AC
After turning the heat off, set the thermostat below room temperature and repeat the walk. Listen for rattles or grinding at the outdoor unit.
- Find the condensate line
Follow the small pipe from the indoor unit, and confirm water is draining after the AC has run for a while.
- Let each system finish
Confirm it shuts off at the set temperature without being switched off by hand.
- Write it all down
Record the date, outdoor temperature and anything weak or noisy, and take a short phone video of any odd sound.
What you might find when you test an HVAC system
| What you notice | What it may mean | What to do |
|---|---|---|
| Starts, reaches every room, shuts off on its own | Normal | Log the date |
| One room gets weak airflow | Blocked register, dirty filter or an airflow problem | Check both, then call a technician. Airflow faults can cut efficiency by up to 15%, ENERGY STAR says |
| AC runs but the air isn't cold | Dirty coils or a refrigerant problem | Call a technician. Refrigerant isn't a DIY job |
| Water around the indoor unit | Clogged condensate drain | Shut the system off and call. Clogs can cause water damage indoors |
| Keeps cycling on and off, or won't shut off | A controls fault | Call a technician |
| Burning smell, scorch marks or tripped breakers | An electrical fault | Shut it off and book a service call |
| Smell of gas | A possible leak and fire hazard | Leave the house and call your gas company from outside |
AC or heat not working after moving in
Tell the right party the same day, in writing. On a resale home, that may be your home warranty company or the seller's agent. A home warranty is a service contract, the FTC notes, so follow its claim steps and read what it leaves out. On a new build, the FTC says builder coverage of heating and cooling typically runs two years.
Don't open gas parts or sealed refrigerant lines. ENERGY STAR lists gas connections, burners, heat exchangers and refrigerant as technician work. It says faulty gas connections are a fire hazard, and a dirty burner or cracked heat exchanger can make equipment run less safely.
If everything works, set up the routine. ENERGY STAR recommends a contractor check-up each year, for cooling in spring and for heating in fall. Check the filter monthly.
Can you test AC in winter? Common questions
Can I test my AC in winter?
Not by running it, in most cases. Inspectors are told not to run an AC or a heat pump in cooling mode below about 60°F because of compressor damage. Check your manual for your unit's limit.
Can I run my furnace in summer to test it?
Yes, for a short test. Raise the thermostat above room temperature, confirm warm air reaches each register, and let it shut off.
How often should a pro service my heating and cooling?
ENERGY STAR recommends a yearly pre-season check-up by a contractor: cooling in spring and heating in fall. You can inspect, clean or change filters yourself each month.
Sources: ENERGY STAR, ahit.com, FTC, jaspector.com
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.