There are some things you should never do to your hvac system. Are you guilty of any of them? Check out the list below to find out—and learn what you can do to give your hvac system the care it needs.

9 things to never do to your hvac system:

1. Ignore any warning or diagnostic lights. Most furnaces have at least blinking lights indicating proper operation when running; many now have digital diagnostic displays for the same purpose. If any warning light goes off, it’s time to call a licensed, qualified hvac service company ASAP.

2. Never change the air filter. This is a biggie and a simple one that most homeowners should be able to address on their own. It should probably be up the list as No 1. This is one of the biggest reasons a system fails to perform in either cooling or heating season. A fresh air filter keeps your system running smoothly and improves your system’s fuel efficiency. Most manufacturers suggest you replace your filter every 30 to 60 days (Err on the lower side if you have pets, children, or live in areas with high pollen or dust.)

3. Rarely clean or service your system. From time to time, as your system ages, it may need to have the blower pulled and cleaned, and/or the evaporator or condenser coils in your a/c cleaned. These procedures can ultimately help your system last longer and definitely help you save on your energy bills along the way. A good cleaning is especially important during the winter for your gas furnace as soot builds up on burners and needs to cleaned regularly.

4. Put off the recommended maintenance. There’s a reason the manufacturer includes an owner’s manual when you buy new heating and cooling equipment. It contains important maintenance guidelines and safe operating instructions for the life of your system.. By following what it says, you can keep your home’s heating and cooling system running smoothly, efficiently, and safely. It will save energy dollars along the way and also help to avoid major breakdowns with big repair bills later. Ideally, you should have your system serviced twice a year. Once, in cooling and again in heating.

5. Never check you’re a/c’s refrigerant levels. Not having the right refrigerant pressures makes for unreliable cooling and reduced efficiency and can also lead to costly repairs. It will take a professional to do this.

6. Run your air conditioner knowing it may be low on charge. Doing so cuts the life of the system—and puts you at risk of having no air conditioning on the most important day of the summer. Your senior’s graduation party with 50 people expected, on a Saturday, or your parents’ 50th anniversary celebration which you planned for the 4th of July. You get the idea.

7. Run your air conditioning in the winter. Air conditioners are not designed to run in low winter temperatures. Doing so can cause damage to the compressor and other working components.

8. Bury the needle. In other words, don’t peg the thermostat down as far as it can go even in the summer when it’s 95 degrees out and feels like a sauna. Doing this doesn’t cool the house better or faster, nor will it ever reach the set point you’re trying to achieve. Trust us, it won’t. You can actually do great damage to the system doing this and ultimately ruin your compressor and bring on its untimely demise. Unless of course, you really just want to replace it anyway.

9. Have an unqualified person work on your system including yourself, Mr. DIY’er. (Keep in mind that you could qualify as “unqualified” if a repair is beyond your skill level.) Take the time to find a qualified contractor. Ask someone you trust for referrals, then do your homework. Check reviews and licensing and insurance information. Your hvac system is the most expensive component replacement in your home besides your roof. Make sure you have someone who is adequately qualified to work on it.

The best way to protect your hvac system is to have a Residential Maintenance Agreement with a qualified HVAC Professional. With an RMA your system will be inspected twice a year. Once in heating; once in cooling to ensure it is functioning properly and at peak performance. And please don’t go on price alone. It costs to run a business so a low price is most likely going to get you a cursory system check at best. You want someone in your home with your best interests at heart. Make sure you have a plan with a company that’s right for you and your system.