Rooftop Unit Troubleshooting Tips
If you’re standing on a step stool, peering into the vents and scratching your head wondering why on earth the inside of your building is the same temperature as the 90-degree weather outside, there could be something wrong with your rooftop unit. In this guide, we’ll provide some potential rooftop unit troubleshooting tips to diagnose the issue quickly.
Power
There are several reasons why your RTU might be turning on and off unexpectedly or won’t turn on altogether. If you’re having electrical troubles, check out some rooftop unit troubleshooting tips to help you restore power:
Faulty Electrical Connection
Faulty electrical connections can occur upon installation or later down the line due to normal wear and tear, corrosion, overheating, moisture, dirt, animals and using non-OEM components to make repairs, to name a few.
Tripped Circuit Breaker
Sometimes, it’s as easy as flipping the circuit breaker switch on and off again. If your circuit breaker continues to trip, this could indicate a more significant electrical problem that needs to be addressed by an HVAC technician.
Blown Fuse
If flipping the circuit breaker switch doesn’t work, the problem could lie with the fuse. However, if your fuse continually blows, it could indicate a more significant electrical problem, as mentioned above.
Dirty Air Filters
Dirty air filters can cause your rooftop unit to overheat. When this happens, it trips the limit or pressure switch, cutting off power to the machine before it causes damage to other electrical components.
Drainage Issues
If your unit doesn’t receive regular maintenance, the drain line or condensate pan can become backed up or clogged with dirt, debris, algae or mold. Sensing this, your rooftop unit will automatically shut itself off to prevent further damage.
Extreme Weather
If there’s a storm raging outside your window or you're currently experiencing record highs and your AC has just turned off, the two are likely related. Power surges caused by lightning strikes, downed power lines, hail damage and extreme heat can all cause your rooftop unit to turn off.
Airflow & Temperature
Is the AC on, but you can’t feel any air coming out, or rather does it seem like it’s pushing around a bunch of warm air, making your building feel hot and stuffy? Let’s take a look at a list of common culprits and some rooftop unit troubleshooting tips:
Dirty Air Filter
If you’re looking at your energy bills thinking, “That can’t be right,” unfortunately, dirty air filters are likely what caused them to skyrocket. Without regular cleaning as recommended by the manufacturer, plugged-up air filters can result in reduced airflow, poor indoor air quality, an increase in utility bills and even damage to RTU components like the heat exchanger and blower motor as the system overheats.
Dirty Evaporator & Condenser Coils
The rooftop unit has to get its air from somewhere and unfortunately, the great outdoors isn’t known for its Febreze freshness or bleach-like cleanliness. Over time, evaporator coils can become clogged with dust, dirt, pollen and other airborne debris when the blower motor sucks in outside air.
To prevent the reduced efficiency and poor indoor air quality caused by dirty coils, it’s important to schedule biannual checkups with your HVAC service technician, who will conduct regular cleaning as per their maintenance checklist.
Blocked Ductwork
If it’s been a hot minute since you’ve changed the air filters or had an HVAC technician look at your RTU, you might be dealing with a severe case of blocked ductwork. Other factors like animal infestations, chronically blocked vents or damaged ductwork might be causing little to no airflow.
Defective Blower Motor
If you feel like the air has become stagnant in your building or some rooms are warmer or colder than others, a faulty blower motor might just be the root of all your problems.
Refrigerant Leak
Another reason your RTU may not be blowing out the cool air you expect is that it's low on or has completely run out of the very thing that makes the magic happen: refrigerant. Now, refrigerant operates in a closed-loop system, meaning you should never have to add more refrigerant like you would gas to a car unless there’s a leak caused by exterior damage, improper installation, corrosion or loose connections.
Note: If you suspect a refrigerant leak, call an authorized service technician immediately, as refrigerant can pose a significant health risk to those not properly trained in its removal and disposal.
Faulty Thermostat
If your rooftop unit is having trouble holding at its setpoint, a faulty thermostat might be the culprit. A thermostat that cannot accurately detect temperature might heat your building up or cool it down too much, causing it to short cycle or sometimes even shut down the system completely.
Noises
Mechanical machinery is known to make a twang or two on initial startup or when it switches between heating and cooling sequences. That said, if it starts to sound like someone is banging on the pipes with a wrench or you notice other unusual noises like squealing, rattling or whistling, it’s time to give your best friend, the HVAC technician, a ring.
- Loose components – If you’re hearing a rattling noise, it’s likely that something has pried itself loose and is now trying to make a run for it. Common RTU components to come loose are brackets, panels, mounts, belts and fans.
- Damaged fan blade – A fan blade can cause a variety of noise issues, depending on how it's been damaged. For example, it can create a rattling or banging noise if it strikes other RTU components as it spins. Or it might have become misaligned or warped, ensuring a loud whirring is heard by all.
- Leaking refrigerant – A hissing or whistling sound is not a good sign and usually indicates that a leak is present. If you suspect a leak, shut off the AC immediately and call an authorized HVAC technician.
- Defective motor or belt – The constant friction belts endure causes them to wear out over time. A worn belt might emit a high-pitched squealing.