Spring in New Hampshire has a way of sneaking up on you. One week you're running the furnace, and the next you're reaching for the thermostat to flip on the air conditioning, only to hear nothing. No hum, no cool air, just silence.
Before you assume the worst, take a breath. Many of the reasons an AC won't start after a long winter are surprisingly simple to fix yourself. This guide walks you through what to check first, what to call a pro for, and how to know the difference.
Start here: the most common culprits
1. Your thermostat isn't set correctly
It sounds obvious, but it's the most overlooked starting point. After months of heating mode, double-check that:
- The system is switched to COOL, not HEAT or AUTO
- The set temperature is lower than the current room temperature — if your house is 68°F and you set it to 70°F, the AC has no reason to kick on
- The fan is set to AUTO (not OFF)
If your thermostat is battery-powered, now is also a great time to replace the batteries. A low battery can cause erratic behavior or prevent startup entirely.
2. A tripped circuit breaker
Your air conditioner runs on its own dedicated circuit, sometimes two (one for the air handler inside, one for the condenser outside). Head to your electrical panel and check for any breakers in the middle position or flipped to OFF.
If you find one, flip it fully to OFF first, then back to ON. If it trips again immediately, stop and call an electrician or HVAC specialist; that's a sign of a deeper electrical issue, not something to force.
3. A clogged or dirty air filter
A severely restricted filter can cause the system to overheat and shut itself off before it ever gets going. If you haven't changed your filter since last fall, pull it out and take a look. If it's gray and dense with dust, replace it before you try starting the system again.
As a rule of thumb, 1-inch filters should be replaced every 1–3 months. Thicker 4–5-inch media filters can last 6–12 months.
4. The condensate drain line is clogged
Modern air handlers have a safety float switch that shuts the system down if the condensate drain pan overflows. After sitting dormant all winter, algae and debris can block the drain line.
Check the drain pan (usually located beneath your indoor air handler). If there's standing water in it, the float switch has likely tripped. You can try flushing the drain line with a mixture of warm water and white vinegar, but if the blockage is stubborn, it's worth having a technician clear it properly.
5. The outdoor unit is blocked or dirty
Walk outside and take a look at your condenser unit. After a New Hampshire winter, it's common to find:
- Leaves, twigs, or debris packed into the fins
- Dirt and grime coat the coil
- Landscaping that has grown too close over the winter
Clear away any debris and gently rinse the exterior fins with a garden hose (spray from the inside out if possible). Make sure there's at least 2 feet of clearance on all sides. Never use a pressure washer; the fins are delicate and bend easily.
6. The disconnect switch was left in the OFF position
Your outdoor condenser unit has a dedicated disconnect box nearby — usually a gray box mounted on the exterior wall. It's not uncommon for this to get switched off during fall service or winterization and simply forgotten. Open the cover and confirm the disconnect is in the ON position.
7. The system needs time to wake up
If your power was recently restored after an outage, or if you just switched the system on for the first time, give it 5–10 minutes to stabilize. Many modern AC units have a built-in time delay to protect the compressor from short cycling. This is normal, just be patient before assuming something is wrong.
When to stop troubleshooting and call a pro
If you've worked through everything above and the system still won't run — or if you notice any of the following — it's time to call an HVAC specialist:
- Ice on the refrigerant lines or the outdoor unit — this usually points to low refrigerant or an airflow problem
- Grinding, screeching, or rattling noises when the system tries to start
- A burning smell coming from any part of the system
- The circuit breaker keeps tripping after being reset
- Warm air is blowing even though the system appears to be running
These are symptoms that go beyond routine startup issues and can cause further damage if the system is forced to run.
The best way to avoid this situation next year
A spring AC tune-up, ideally scheduled in April or May before the first heat wave, catches small problems before they strand you without cool air. During a professional inspection, our HVAC specialists will:
- Clean and inspect the evaporator and condenser coils
- Check refrigerant levels and look for leaks
- Test electrical connections and capacitors
- Lubricate moving parts
- Verify thermostat calibration
- Clear the condensate drain line
Think of it like a first oil change of the season for your car. It's a small investment that extends equipment life and maintains high efficiency.
We're local and ready to help
GSMS has been serving homeowners across southern New Hampshire for years, and spring is one of our busiest times for exactly this reason. If your AC isn't cooperating, our team can diagnose the problem fast and get your home comfortable before the heat sets in.
Request Service Online or call us at 603-424-8258 - we're here when you need us.
