Ask an Expert: Diagnosing Technical Failures on Your HVAC Unit

Anyone who’s ever looked into making a minor repair on their air conditioner or furnace will tell you: HVAC units are complicated! Compressors, motors, fans, drain lines—there’s a lot going on in your home’s system. Today we talked to HVAC repairman Chris Tinney, to address the more technical side of repairs and find out more about some exciting new products that are just starting to infiltrate the market.

Young repairman fixing an industrial air conditioning compressor.

Let’s jump right in. We’ve heard that you’ve installed solar-powered HVAC units before, and we’re dying to hear all about them. Can you tell us more about those?

They’re Lennox products. Whenever they get above 17 or 18 SEER, on a Lennox, at least, they’re solar-ready. Essentially, that means that if you have solar panels and you’ve got a hookup for it, you can add the solar power to the actual unit itself.

They do run dead quiet, and they’re very efficient. The problem is, you go from a circuit board of about maybe six inches long to a board that’s about two and a half feet. So if that board ever fails, then it’s a huge issue. In my experience, if you have a part that’s going to fail or can fail, it needs to be small, and pretty readily available—universal equivalents are necessary—because a lot of times you can’t go to a manufacturer and get the exact piece.

Essentially, every time one of those boards fails, you have to call the supply house, then the supply house calls the manufacturer, the manufacturer sees if the supply house has any in stock—and 95 percent of the time, when it’s one of those boards, they don’t. So you end up waiting while they order the board and have it shipped—probably a week at minimum.  But with a traditional HVAC unit, a repair person can be in and out of the house in about an hour and a half.

It sounds like you end up doing a lot of repairs. What would you say is the most common kind of repair you see?

Capacitors—that’s 95 percent of the time. And capacitors are common because when it’s really hot out, they overwork, and they swell—that’s what gives the compressor and the fan juice to kick on. If that fails, nothing is going to work. I have six drawers on my truck [filled with repair supplies]. I have a whole drawer dedicated to just capacitors.

Okay, if capacitors are such a common problem, how can a homeowner diagnose that issue? What are the signs that a capacitor is out?

The outdoor unit’s not running—it will just sit there and hum. The contactor on the unit—even if the unit’s essentially dead, it will still send the signal from the inside to the outside. And what that will do is, even if there’s no power, the unit will sit and hum really quietly.

In normal cooling mode, if the compressor’s not cooled off, it can get above 130 degrees Fahrenheit. Once it hits around 110 or 120, it will just shut off. The fan will quit, and the compressor will overheat, and everything will shut down.

What would you say is something that homeowners can do to limit problems before they happen?

  • Unplug your power, and clean your outdoor coil. Those things are like giant vacuum cleaners. If you mow the grass while it’s running, or if there’s a lot of dirt near it, or if you have dogs that like to hang out by it—which they do—it will get so covered in dirt and grass and hair that it won’t pull the air through like it’s supposed to, and cool off the compressor, resulting in the compressor overheating.
  • Pour bleach or vinegar down your HVAC drain line. A pretty common problem is clogged drain lines. If you do not have a drain safety, and the unit is in your attic, it will flood and just destroy the house. If it’s in a closet, it will destroy your floor. Without a drain safety, if it’s in a closet and you pour vinegar down it regularly, you can really prevent that damage. Cleaning out your drain is a piece of cake. If you have one of those CO2 shooters, you can blow out your drain, or if you have a wet vac, you can suck it out.
  • Use filters. Depending on how many dogs or cats or people or how open the house is, use filters. Don’t buy the mesh kind. Always get pleated—you can go as cheap as you want as long as it’s pleated. And it should have the metal on the back. The metal will essentially keep the system from sucking that filter in if it gets too dirty.

In the summer time, if it’s you and one other person in your home, changing the filter every two months is acceptable. If you have a pet, drop it down to monthly. It all varies depending on how dirty your house is, how open it is, and how many pets your have—but essentially, your filter should never be black when you change it. If anything, change it as soon as you see that it’s a light gray. The dirtier your filter, the harder it’s working. The harder it’s working, the less time it will last, which will hurt the compressor and mess up fan motors.

Pesticide around your outside units is a pretty good idea, too. Ants, lizards, spiders, and snakes will crawl in and affect your unit’s performance.

Service technician checks utilities

What about smart HVAC systems; have you ever seen one of those?

There are smart HVAC units, and they usually require a smart thermostat. Usually, those units will have a large circuit board as well. You can have the safety switches without having a board. The normal ones are about a four by six, and the bigger ones can go up to ten inches—that’s huge. But they work really well.

So essentially, having all the controls on the system makes it a more complicated unit, which in turn makes it more difficult to repair?

Yes, when it fails, it’s never going to be an easy fix. The higher the efficiency, the smarter the unit. You get a 14 or 15 SEER, you get the basics. You’ll have the safety switches, which are good to have. Essentially, that helps a repair person diagnose the unit.

What advice would you give a homeowner who is about to buy a new AC, furnace, or heat pump?

Stick to the name brands. Always get the warranty. If you don’t go to the right place, you can spend almost $10,000 for a new system. If you pay $10,000 for a new system and it breaks down, and you don’t have it warrantied, then you still have to spend more money to fix it. Get the warranty—a lot of companies will give you a year warranty for their labor. Call them out—say, “hey, this thing made a weird noise, come and check it out for me.”

Empowering homeowners to get their HVAC units repaired—we’re totally on board with that. Thanks for talking with us today, Chris.

Thanks for having me!

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