When your thermostat set to cool but ac not turning on becomes your reality on a hot BC day, it is frustrating and confusing. The good news is that many causes are simple to diagnose and fix at home. This guide explains why your thermostat set to cool but ac not turning on situation happens, what to check first, and when to call Eco Pro Heating. Whether you live in North Vancouver, Burnaby, Chilliwack, or elsewhere in BC, these steps apply to central air conditioners, ductless mini splits, and heat pumps. If your thermostat set to cool but ac not turning on persists after the basics, professional help is the safest path.
Start here when you see thermostat set to cool but ac not turning on on your display. Confirm the mode is Cool, the setpoint is lower than room temperature, and the fan is on Auto rather than On. Fan On moves air without cooling, which can make the system seem like it is running when it is not. If you use a smart thermostat, temporary glitches or Wi Fi drops can also cause the thermostat set to cool but ac not turning on issue. Reboot the thermostat and its app, or perform a manufacturer reset.
Tip: Remove batteries for thirty seconds on battery models, then reinstall. For smart models, use the reset option in settings.
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If your thermostat set to cool but ac not turning on remains after checking settings, inspect power. Look for a tripped breaker labeled HVAC or AC and fully flip it Off then On. Outside, open the service disconnect near the condenser to make sure it is seated. On mini splits, inspect outdoor wiring for damage. Repeated breaker trips during a thermostat set to cool but ac not turning on event suggest a failing capacitor, shorted wiring, or compressor issues that need a technician.
Still nothing? Repeated breaker trips suggest an overloaded circuit, faulty wiring, or a failing capacitor that needs immediate attention.
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Low batteries can cause a thermostat set to cool but ac not turning on scenario because the thermostat cannot reliably send a cooling call. If the screen flickers or lags, replace the batteries with fresh name brand cells, wait one minute, then recheck. Some models lose schedules when batteries die, which can prolong the thermostat set to cool but ac not turning on headache until you reprogram them.
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Neglected air filters are one of the top culprits behind poor AC performance. If your filter is clogged, airflow drops, coils get too cold, and the system can shut down automatically to protect itself.
How to spot the issue:
Fix:
Pro tip: Don’t just replace filters when it smells funky. In BC's pollen-heavy seasons, check every 3–4 weeks.
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If your AC system can’t drain condensation properly, a float switch may automatically shut it down to prevent water damage.
Symptoms of a clogged drain line:
Quick fix:
Advanced tip: Use a wet/dry vac outside at the drain line exit to suction out sludge if it’s deeply blocked.
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Clicks, hums, or a short buzz followed by silence often point to a failed start capacitor or a compressor that cannot start, both of which present as thermostat set to cool but ac not turning on. Do not attempt to replace capacitors yourself since they can hold a charge. Schedule service if the outdoor fan does not spin, the unit starts and stops within seconds, or breakers trip whenever cooling is requested. These patterns are classic thermostat set to cool but ac not turning on clues that require a certified pro.
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If your room is warm but your thermostat claims it's already 21°C, it may need calibration.
How to check:
What causes bad calibration?
Solutions:
We install and configure smart thermostats throughout BC
During maintenance, the outdoor disconnect can be left open. When that happens, you get thermostat set to cool but ac not turning on even though indoor components seem normal. Open the disconnect box by the condenser, remove and reinsert the pull handle or toggle the breaker Off and back On. A firm seat often resolves a stubborn thermostat set to cool but ac not turning on.
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You’ve checked settings, replaced the filter, reset breakers, and flushed lines—but your AC still won’t turn on.
At this point, DIY ends and it’s time for a trained tech to take over.
Call us if you notice:
We’ll inspect your entire system: wiring, relays, refrigerant levels, motors, and more.
Why does my thermostat say cool but the AC is off?
Most thermostat set to cool but ac not turning on cases are caused by a tripped breaker, a dirty filter that iced the coil, a clogged drain float switch, weak thermostat batteries, or an outdoor disconnect that is not seated.
Will a bad capacitor cause thermostat set to cool but ac not turning on?
Yes. A failed start capacitor prevents the compressor or fan motor from starting, which looks like thermostat set to cool but ac not turning on even though the thermostat is working.
Can low refrigerant be the reason for thermostat set to cool but ac not turning on?
Low charge usually causes poor cooling rather than a full stop, but if icing occurs the system can shut down on protection and appear as thermostat set to cool but ac not turning on. Only a licensed tech should check and correct charge.
How often should I change filters to avoid thermostat set to cool but ac not turning on?
Check monthly and replace every one to three months depending on dust, pets, and pollen. Regular changes prevent icing and airflow faults that trigger thermostat set to cool but ac not turning on shutdowns.
Could the thermostat itself be faulty?
Yes. Failed sensors, miscalibration, or power issues in the thermostat can cause thermostat set to cool but ac not turning on. Battery replacement, reset, or thermostat replacement may be required.
If your thermostat is set to cool but the AC is not turning on, don’t jump to conclusions. Start with the basics:
If none of that works—or if you hear buzzing, see water, or smell burning—it’s time to get professional help.
Eco Pro Heating offers fast, reliable AC service across BC, including repairs, system upgrades, and preventive maintenance. We also help homeowners access rebate programs for high-efficiency heat pumps and smart thermostat installations.
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