What to Do Before You Call an HVAC Technician
Something is wrong with your heating or cooling — and your first instinct is to pick up the phone. That is usually the right call. But before you do, it is worth spending five minutes running through a few quick checks.
Some of the most common service calls we receive at CSO Mechanical turn out to be simple fixes a homeowner could handle themselves. Running through this checklist first can save you time and money — and if you do still need a technician, it helps us diagnose the problem faster when we arrive.
Table of Contents
Check the Thermostat
Start here every time. Confirm:
The thermostat is set to the correct mode — Cool in summer, Heat in winter
The set temperature is at least 3-5 degrees above or below the current room temperature
The fan is set to Auto, not On (fan set to On blows air continuously even when not heating or cooling)
The batteries are not dead — low batteries cause thermostats to behave erratically
If your thermostat is programmable or a smart thermostat, check that the schedule is not overriding your manual settings.
2. Check the Air Filter
A clogged air filter is one of the most common causes of HVAC problems in Indianapolis homes — and one of the easiest to fix. A dirty filter restricts airflow, which can cause:
Weak or no airflow from vents
The system to freeze up or overheat
The unit to run constantly without reaching the set temperature
Pull the filter out and hold it up to a light. If you can not see light through it, replace it before calling for service. Filters should typically be replaced every 1-3 months depending on usage and whether you have pets.
3. Check the Circuit Breaker
Your HVAC system runs on dedicated breakers in your electrical panel. If the unit is not turning on at all, go to your breaker box and look for any tripped breakers — they sit in a middle position between On and Off.
Reset a tripped breaker by switching it fully Off and then back On. If it trips again immediately, do not keep resetting it — that is a sign of an electrical issue and a technician needs to take a look.
4. Check the Power Switch on the Unit
Most furnaces and air handlers have a dedicated power switch nearby that looks like a standard light switch. It is easy to bump off accidentally, especially in utility rooms or storage areas.
Make sure the switch is in the On position. Also check that the access panel on the unit is fully closed — many systems have a safety shutoff that cuts power when the panel is open or ajar.
5. Check the Outdoor Unit
If your AC is running but not cooling, head outside and take a look at the condenser unit:
Clear any debris — leaves, grass clippings, or dirt buildup — from around and on top of the unit
Make sure the fan on top is spinning when the system runs
Look for ice on the refrigerant lines or the unit itself — if you see ice, turn the system off and call a technician
Keep at least two feet of clearance around the unit at all times.
6. Check Your Vents
Walk through your home and confirm:
All supply vents are open and unobstructed by furniture, rugs, or curtains
Return air vents (the larger grilles that pull air back into the system) are not blocked
Closing too many vents actually increases pressure on the system and can cause problems — a common misconception is that closing vents in unused rooms saves energy.
7. Check the Condensate Drain Line
Your AC removes humidity from the air and drains it through a condensate line. If that line gets clogged, water backs up and many systems automatically shut off as a safety measure.
Look for standing water near your indoor air handler or a wet spot around the unit. A clogged drain line is a straightforward fix — but it does require a technician to clear properly.
8. Write Down What You Are Experiencing
If you have been through the checklist and still need to call, take two minutes to note:
What the system is doing (or not doing)
When the problem started
Any unusual sounds, smells, or error codes on the thermostat
How old the system is and the brand if you know it
This information helps your technician arrive prepared, which means a faster diagnosis and less time on site.
When to Skip the Checklist and Call Immediately
Some situations do not call for troubleshooting — they call for a phone call right now:
You smell gas near your furnace
Your carbon monoxide detector is going off
You see sparks or smoke near any part of the system
You have no heat in freezing temperatures or no AC in extreme summer heat
In those cases, call immediately. For the gas or CO situations, leave the house first.
Ready to Schedule a Service Call in Indianapolis?
If you have been through the checklist and your system still is not right, CSO Mechanical LLC is ready to help. We serve Indianapolis, Carmel, Fishers, Noblesville, Greenwood, Westfield, Zionsville, Avon, and Plainfield.
Call (317) 372-1608 or visit our contact page to schedule service. Licensed, bonded, insured — and backed by 30+ years of hands-on HVAC/R experience.