HVAC Out? 5 Common Causes and Quick Fixes for Each

Problems with your HVAC system can make life uncomfortable at best and intolerable at worst — especially in extremely hot or cold weather.

Fortunately, you can solve several common issues with a DIY HVAC repair. Try the following fixes before calling a technician.

1. Dirty Condenser Coils

The problem: Dirty condenser coils in your air conditioner stop heat from transferring from the refrigerant to the outside air as efficiently. Therefore, you may notice that your AC unit isn't cooling your home as well as it used to. It also forces your AC to work harder, resulting in higher energy bills. Eventually, your AC unit may break down completely.

The fix: Fortunately, cleaning dirty condenser coils is a simple HVAC maintenance task. Start by removing visible debris from the coils with a coil brush and straightening any bent fins with a fin comb. Next, apply a foaming coil cleaner and leave it to stand for around 10 minutes before rinsing with a hose.

When to call a professional: Strange noises coming from your condenser unit could be a sign of an underlying issue. Call a professional to diagnose and repair the issue if you hear unusual sounds or notice visible coil damage.

2. Low Refrigerant

The problem: Refrigerant is the chemical inside your AC unit that removes heat from the air and transfers it outside. Your AC unit requires a consistent refrigerant level, known as a charge, to keep your home cool. Cracks in the refrigerant lines or compressor can allow the refrigerant to escape, potentially damaging the compressor and causing breakdowns.

The fix: Leaking refrigerant requires a professional to fix, but it's easy to check whether you have a refrigerant leak yourself. Leaking refrigerant evaporates, so you won't see any telltale drips. However, it will reduce the temperature of the indoor evaporator coil, causing it to frost over.

When to call a professional: Schedule a professional HVAC repair as soon as you notice signs of a refrigerant leak. Acting quickly can prevent expensive compressor damage. An HVAC technician can repair the leak and recharge the refrigerant to the correct level.

3. Dirty Filter

The problem: AC air filters gather hair, dust and other debris. A dirty air filter forces your air conditioner to work harder to cool your house down, so you may notice hot air coming from the back of the unit.

Your unit may stop cooling air efficiently or even pump warm air into your house, and the extra pressure on your system could increase your energy bills. People with allergies may experience an increase in symptoms as the unit blows out pet dander and other allergens. 

The fix: You can quickly tell if a dirty filter is to blame for your AC problems by hanging a white sheet around 5 inches from the vents. It will turn grey within an hour or two if your filter is dirty. Replacing the filter should solve the issue, and it's worth setting a reminder to replace the filter every three months or so to prevent a recurrence.

When to call a professional: Call an HVAC tech if your AC still isn't working properly after replacing the filter.

4. Pilot Light Is Out

The problem: The pilot light on your furnace ignites the gas when you turn your heater on. Your furnace will stop working if your pilot light goes out because its safety mechanism will prevent any more gas from entering the system.

The fix: You can often relight your pilot light to turn your furnace back on yourself. The method for relighting a pilot light depends on your furnace make and model, so defer to the manufacturer's instructions.

When to call a professional: It's wise to call a professional to check your furnace even if you manage to relight the pilot light, especially if it keeps going out. A pilot light outage can be a sign of a more serious issue with your furnace.

Never attempt to relight your pilot light if you smell gas. Instead, evacuate your home and call your utility company to turn off the gas supply to your house. You should then call an HVAC professional to diagnose the issue.

5. Closed or Blocked Vents

The problem: Closed or blocked vents stop cold air flowing from your AC system into your home. Sometimes, homeowners close their vents deliberately because they think it will allow their system to cool other rooms more efficiently.

However, closing your air vents is never a good idea. It can cause air to back up into the ducts and put pressure on the heat exchanger, increasing the likelihood of leaks and making your AC less efficient. The worst-case scenario is that the added pressure could crack the exchanger and cause a potentially lethal carbon monoxide leak.

The fix: Open all the vents in your home and ensure that there are no objects blocking airflow. You can maximize airflow to certain areas by closing other vents no more than 75%. Never shut them entirely.

When to call a professional: Hire a professional HVAC technician to inspect your system if your AC system isn't distributing cold air effectively.