Why Your AC or Furnace Isn't Working: A WNC Troubleshooting Guide

There's never a good time for your HVAC system to quit. The AC runs all day but the house won't cool, the furnace kicks on and blows cold air, or you walk outside to find your heat pump encased in ice. Before you panic — or pay for a service call — some of these problems have simple causes you can check yourself.

At Comfort Pros, we'd always rather help a Brevard homeowner fix a five-minute problem than charge them for one. This guide walks through the three most common HVAC complaints we hear, what usually causes each, and the point at which it's time to call a professional.

In this guide

• Why is my AC not cooling?
• Why is my furnace blowing cold air?
• Why is my heat pump frozen outside?
• When to call a professional
• Frequently asked questions

Why is my AC not cooling? (Running but blowing warm air)

When your AC runs constantly but the house stays warm, the cause is usually one of a few things — and some you can check in minutes:

• A dirty air filter. This is the number-one culprit. A clogged filter chokes airflow, so little cool air actually reaches your rooms. Check it first, and replace it if it's dirty.
• Thermostat settings. Make sure it's set to "cool" and the fan is on "auto," not just "on" (which blows unconditioned air between cycles).
• A blocked or dirty outdoor unit. Weeds, leaves, or debris packed around the outside condenser stop it from releasing heat. Clear a couple of feet around it.
• A tripped breaker. If the outdoor unit isn't running at all, check your breaker panel.

If the filter is clean, the thermostat is right, and the unit is clear but you're still blowing warm air, the likely causes are low refrigerant or a failing component — and those need a professional. Our AC repair team can diagnose it quickly.

Why is my furnace blowing cold air?

A furnace that runs but blows cool or lukewarm air is a common winter complaint. Start with the easy checks:

• Thermostat fan setting. If the fan is set to "on" instead of "auto," it blows air even when the furnace isn't actively heating — so you feel cool air between cycles. Switch it to "auto."
• A dirty filter. Just like with AC, a clogged filter restricts airflow and can cause the furnace to overheat and shut off its burners, leaving only the fan running.
• Pilot light or ignition. On older units, a pilot light can go out. Newer units use electronic ignition that can fail and needs professional attention.
• Thermostat batteries. Dead batteries can cause the system to behave erratically — an easy fix worth ruling out.

If the basics check out and your furnace still won't heat, it could be a flame sensor, ignition, or gas-supply issue — all of which call for a pro. Our heating repair team handles these safely.

Why is my heat pump frozen outside?

Seeing ice on your heat pump in winter can be alarming, but a little frost is actually normal — heat pumps run a defrost cycle to melt it off. It becomes a problem when the unit is encased in ice and can't clear itself. Common causes include:

• A blocked defrost cycle. If the defrost cycle isn't working, ice builds up instead of melting away.
• Restricted airflow. A dirty filter or blocked outdoor unit can lead to freezing.
• Low refrigerant. This causes the coils to run too cold and ice over.
• Drainage issues. Water pooling and refreezing around the unit.

If your heat pump is lightly frosted, give it time to run its defrost cycle. But if it's buried in ice, turn it off to prevent damage and call a professional — running a frozen heat pump can harm the compressor. Keeping up with regular HVAC maintenance is the best way to prevent freezing in the first place.

When to call a professional

Many HVAC hiccups come down to a dirty filter, a thermostat setting, or a blocked outdoor unit — all things you can check yourself in a few minutes. The ENERGY STAR maintenance checklist is a good reference for the simple upkeep that prevents most of these problems.

But some issues aren't DIY territory. Anything involving refrigerant, electrical components, gas, or a unit that won't respond to the basic checks should be handled by a licensed technician — both for your safety and to avoid turning a small repair into a big one. If you've run through the checks here and your system still isn't working, a quick system diagnostic will pinpoint the real cause fast.

Frequently asked questions

Why is my AC running but not cooling?

The most common reasons are a dirty air filter, a thermostat set incorrectly, or a blocked outdoor condenser. If those all check out and it's still blowing warm air, it's likely low refrigerant or a failing part, which needs a professional.

Can a dirty air filter really stop my AC from cooling?

Yes — it's one of the most common causes. A clogged filter chokes airflow so little cool air reaches your rooms, and it can even cause the system to freeze up. Checking and replacing the filter is always the first thing to try.

Why does my furnace blow cold air sometimes?

Usually it's the thermostat fan set to "on" instead of "auto," which blows air even between heating cycles. A dirty filter causing the burners to shut off is another common cause. If neither fixes it, the ignition or flame sensor may need service.

Is it normal for my heat pump to ice up in winter?

A little frost is normal — heat pumps run a defrost cycle to clear it. But if the unit is completely encased in ice and can't melt it off, turn it off and call a professional, since running it that way can damage the compressor.

Do you offer AC and heating repair across Transylvania County?

Yes — we're based in Brevard and serve the whole county. See our Transylvania County page or our local Brevard HVAC page for everything we cover.

Still not working? We're here to help.

If you've tried the simple checks and your AC or furnace still won't cooperate, don't sweat it — or freeze. The team at Comfort Pros gets Western North Carolina homes back up and running fast, with honest diagnostics and no unnecessary upsells.

Call us at (828) 393-0024 for fast, friendly service, or request help online. As a local, AAA-rated, family-owned team, we'll figure out what's wrong and fix it right — upfront pricing, no surprises.