22 Simple Heating and Air Conditioning Fixes

Updated: Jan. 10, 2024

Even a beginner can solve common furnace and air conditioning problems — and save money!

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Woman Adjusts Thermostat
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Fixing Heating and Air Conditioning

When your heating and cooling system isn’t working properly, you might throw up your hands and call for help, thinking the solution must be outside your skill set. You might be surprised to learn the most common furnace and air conditioning problems are simple to resolve.

Here are 22 easy furnace and air conditioning fixes that take minutes or less and can save you a wad of cash.

Meet the Expert

Tim Adams is the service manager at Standard Heating & Air Conditioning in Minneapolis.

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Check Filter
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Check Your Filter

A dirty filter causes your system to work harder, resulting in premature failure of parts. A dirty filter can also cause a shutdown.

How often your filters need changing depends on many factors. Do you live in a high-traffic zone? Do you have pets? Do you leave the windows open? Write the date on your filter to help keep track of when it needs to be changed. Don’t forget about changing furnace filters in the summer. They’re also for the A/C.

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Start At The Thermostat
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Start at the Thermostat

Most thermostats have a switch so you can set the system to “heat” or “cool.” Make sure yours is set to the proper function.

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Replace Thermostat Batteries
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Replace Thermostat Batteries

If your thermostat doesn’t seem to be working, try changing the batteries. They typically need to be replaced annually. After you’ve replaced the batteries, your thermostat might revert to its default settings and need to be reprogrammed.

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Run A Quick Power Test
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Run a Quick Power Test

To see if the furnace is getting power, set your thermostat to the “fan” position. If you don’t hear the fan turn on, there’s a good chance there’s no power to the furnace. If there’s power, check the furnace itself.

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Technician Repairing Gas Furnace Using Digital Tablet
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Check Inside the Furnace 

New furnaces have fault codes, like cars. Check for codes or flashing lights, then look in your owner’s manual or online to diagnose the problem.

If you can’t decipher the code or don’t want to bother with it, send a video to the repair technician. It’s helpful for the tech to know what the problem might be before coming out.

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Check The Circuit Breaker
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Check the Circuit Breaker

A breaker can trip without fully moving to the “off” position. Flip it “off,” then back to “on” to be sure that’s not the issue.

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Dirty Drainpipe From Air Conditioning
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Make Sure Water Can Drain

High-efficiency furnaces collect water as a by-product of combustion. In cooling mode, your A/C collects water from the air. In either case, that water needs to drain away. If not, your furnace will leak water or just shut down.

First, make sure water is dripping from the end of the tubing when the system is running. If you don’t see drips, clear the line by blowing through it with your mouth. Don’t use a compressor; too much pressure can blow connections apart.

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Clean The Igniter
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Clean the Igniter

Hot surface igniters are the most common ignition system on modern furnaces. They take the place of standing pilot lights and electronic igniters.

Clean the dust off the hot surface igniter by leaving the igniter in place and blowing air through a straw. This part breaks really easily; don’t even touch it. In fact, when you replace the furnace cover panels, do so gently to avoid breaking the igniter.

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Check Condensate Pump
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Check the Condensate Pump

If you have a condensate pump, listen closely to make sure it runs. If not, try resetting the GFCI outlet that powers it. If that doesn’t work, you may need a new pump (about $60).

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Check The Safety Switch
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Check the Safety Switch

Furnace cover panels often activate a safety switch when the panel is removed or left even slightly ajar. Check to see that the panel is fully closed.

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Is Gas Valve On
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Check to See if the Gas Valve Is On

Find the gas line for your furnace, then locate the valve. The valve handle should be parallel to the gas line. If it’s perpendicular, there’s no gas going to the furnace.

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A Humidifier Can Cause Your Furnace Filter to Clog

If you use a portable humidifier, always fill it with distilled water. Non-distilled water can cause a calcium buildup on your furnace filter and completely clog it in a matter of days. The buildup is white, so a white filter will still look clean when it’s actually clogged.

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Check Airflow
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Check Airflow

On the outside of your house, you may have a couple of PVC pipes sticking out of the wall. One points downward (furnace air intake) and one points horizontally or upward (furnace exhaust). Drifting snow, ice buildup or nesting animals can block one or both of these pipes, causing a high-efficiency furnace to shut down.

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Check For Power
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Check for Power

A furnace has a power switch nearby, often right on its housing. It looks just like a light switch. Check to make sure this switch hasn’t inadvertently been switched to the “off” position.

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Can Your Furnace Breathe
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Can your Furnace Breathe?

Your furnace room is likely supplied with a “makeup air” duct. It’s a large, flexible, insulated duct that probably drops into a bucket. This duct supplies your house with fresh air to replace oxygen lost in combustion.

Because furnace rooms often double as storage areas, it’s easy to inadvertently block that duct. If it’s blocked, kinked or squashed, it can cause your furnace to shut down, because there’s no oxygen for combustion and it won’t ignite. Typically, this isn’t a big problem in old, drafty homes. But in new super-insulated homes, it can be an issue.

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Clean Pilot
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Clean the Pilot

A dirty pilot can cause the flame sensor (or thermocouple) to get a false reading indicating the pilot isn’t lit. Clean it off with a blast of air. Direct air to the exact spot with a drinking straw. Newer furnaces have hot surface igniters instead of pilots and electronic igniters.

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Check For Blocked Registers
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Check for Blocked Registers

Have you noticed large temperature swings in certain rooms or an unusually short furnace cycle time? Make sure there’s nothing blocking the air returns.

Returns pull air out of the room and back to the furnace, while supply registers blow air into the room. You can check the return airflow by holding a piece of paper against the return register. The paper should stick to the register. If it doesn’t, there’s an airflow problem.

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Adjust The Damper
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Adjust the Damper

If your heating ducts also serve as air conditioning ducts, they likely have dampers that require adjusting for seasonal changes. The seasonal settings should be marked on the duct.

Two-story homes often have separate supply trunks to serve the upstairs and downstairs. To send more warm air downstairs (winter setting) or more cold air upstairs (summer setting), adjust the damper handle on each supply trunk.

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Check Drain Line
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Does It Seem Like the A/C Isn’t Working?

Condensation in your A/C attracts dust. When the condensation flows out the drain line, that dust can plug the line.

Check the end of the drain line to see if water is coming out. If not, blow the line clear. Usually lung power is sufficient. Compressed air may cause something unseen to come apart. Also, remove the cap from the evaporator coil and clean out the tube with your finger.

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Check For Mice and Other Pests

Your condenser unit has an access panel behind where you’ll find the wiring and connections. Because this is an outdoor unit, it’s often an appealing residence for critters. After shutting off power at the breaker, remove the access panel and check for broken or chewed wires. Replace them as needed.

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Check Fuses In Disconnect Block
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Check Fuses in the Disconnect Block 

These fuses are typically located in a box mounted to the house near the condenser. Set your multimeter to the lowest Ohms value and touch the red and black leads to opposite ends of each fuse. If you get a numerical reading, the fuse is good. But a zero, a minus symbol or an infinity symbol (∞) indicates a blown fuse. 

Take your old fuses along to the home center to verify that the new ones match. Replacing a fuse can get you up and running again quickly. But if your unit regularly blows fuses, there’s some­­thing else wrong with your system.

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Investigate Condenser Unit
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Investigate Your A/C’s Condenser Unit

Is your A/C blowing air, but not cold air? Does the condenser seem louder than usual? If it’s working too hard, it may just shut off. The condenser coil, located inside the outdoor unit, is probably dirty.

To clean the condenser coil, spray it off. Don’t use high pressure. Put your thumb over the end of the garden hose or use a sprayer nozzle. More pressure than that can bend the fins.

The cleaning schedule for condenser coils, like the timing of filter changes, depends on environmental conditions. Cottonwood seeds can blanket your condenser coil in a day. Make a habit of cleaning the coil regularly.