Home Home Improvement AC SOS: 7 Common HVAC Issues
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AC SOS: 7 Common HVAC Issues

hvac issues

Does your furnace blow cold air while your air conditioner blows warm air? Is your HVAC system always making strange noises? Perhaps your HVAC shuts off randomly or won’t turn on at all.

If so, take some comfort in knowing that these are all very common HVAC issues. Even better, we’re going to help you troubleshoot these problems with the following guide.

Below, we’ve listed the most common HVAC problems along with the instructions on how to fix them. Read on to learn exactly what to do about your particular issue.

Try These Solutions First

First thing’s first. Almost every issue on this list can be solved or prevented by these three maintenance steps. Before you do anything else, make sure these steps are taken care of.

1. Change Your Air Filter

Your air filter traps dust and other particulate matter as the HVAC fan blows your indoor air through it. It must be changed regularly or else it will become full to capacity and clog up your system. This puts extra strain on your HVAC, which wears it out faster and causes lots of other problems.

According to Schneidermechanical.com, you should change your air filter monthly, especially during seasons of heavy use. However, some filters can go a maximum of 3 months before needing changing.

2. Set Your Thermostat

It may seem like your HVAC is on the fritz. But maybe the thermostat is just set incorrectly.

To remedy this, there are 3 things you need to make sure of. You must ensure that:

  • You understand all the features of your thermostat and how to use them
  • The thermostat is set to your desired settings
  • No one else in the house is changing the thermostat settings behind your back

These steps often correct issues like the HVAC turning on/off at inappropriate times.

3. Check Your Furnace’s Fuel Level

If your furnace isn’t warming your house, check the fuel level. It may be that you’re simply out of fuel.

Troubleshooting Other HVAC Issues

Hopefully, the steps above have just solved all of your HVAC problems. If not, find your issue below to learn what to do.

1. High Heating/Cooling Bills

Is your energy bill this heating/cooling season abnormally high? This means that the HVAC system is working too hard.

It may help to lubricate your fan if you know how to do so. Otherwise, your HVAC probably:

  • Has a worn-out component that needs repairing/replacing
  • Has a blockage (possibly a full air filter)
  • Is too old and worn out
  • Is too small for your house

In these instances, you need to call a professional HVAC technician to come and take a look at it.

2. A Constantly Running HVAC

If your fan’s running all the time, this is why your energy bill is high. The same causes/solutions we just described apply here as well.

3. Warm AC Air

If your AC air is warm, check the condenser unit for signs of icing. Deice it if necessary.

The problem could also be caused by a clog or low refrigerant levels. Get professional help for these issues.

4. Your HVAC Randomly Shuts Down

If your HVAC keeps shutting off very soon after it just came on (and doesn’t reach the desired indoor temperature), it’s probably an electrical issue. It means that the system’s auto-shutoff feature kicks in like a circuit breaker to prevent an overload. Call a professional to fix this.

5. Bad Smells

Why does your heater/AC smell like mold, smoke, or urine? It’s probably because there’s mold, burning electrical wires, or dead animals somewhere in the system.

Long story short, a lot of things can cause a lot of smells to come from your HVAC. And all of them are really big problems that require immediate, professional help.

6. Moisture Leaks

Never take moisture leaks for granted. While it may be a harmless condensation leak, it could be a deadly refrigerant leak. Shut the system down and call for emergency HVAC service right away.

7. Weird Noises

Malfunctioning HVACs make lots of weird noises. Here are the most common examples and what to do about them.


If your HVAC is uncomfortably loud, it either needs lubricating or repairing. If lubricating doesn’t work, call it in.

Metal Grinding

This noise is another of those “emergency HVAC repair” situations. It’s exactly what it sounds like: metal components grinding against each other. This could easily spark a house fire, so shut the system down and call it in.

Screeching, Rattling, Clanking, or Any Other Sounds From the Fan

There are 3 main causes of noises coming from your fan:

  • It needs lubricating
  • There’s a loose component
  • There’s debris contacting the fan blade

Thus, your solutions are to remove debris, lubricate the fan, or call it in.

A Loud Pop

If you hear a loud bang or pop whenever the system comes on, it’s your air ducts adjusting to the temperature change. This means that either they’re not insulated well enough or they’re installed improperly.

The good news is that this problem isn’t dangerous, only annoying. The bad news is that you may need your ducts replaced to solve this. First, though, try insulating the ducts.

A Rumbling Furnace

When you hear your furnace rumbling, check if the sound’s coming from the pilot light area. Try resetting the pilot light. If that doesn’t work, get the igniter cleaned or replaced.

Stay Prepared For HVAC Issues With This Guide

Don’t let your HVAC issues get out of control. Resolve them with the DIY fixes in this guide or get professional help if necessary. To make sure you don’t forget these solutions, keep this page bookmarked.

Next, learn what to do about termites in your house or how to tell if you need roof replacement. Find these posts and other important tips on our Home Improvement blog.

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