Short cycling is a common issue that can affect the performance of an HVAC system. It occurs when the compressor, the main component of an HVAC system — turns on and off more frequently than it should. This places extra strain on the unit, leading to higher energy costs and uneven temperatures throughout the home.

While short cycling can be an unsavory nuisance, the good news is that it can be avoided by addressing the underlying causes. The only way to know for sure what’s causing your HVAC unit to short cycle is to get a professional inspection, but the culprit is likely one of these 11 causes.

1. Dirty Air Filter

A dirty air filter can cause the system’s blower motor to draw too much current. This may lead to an overload that trips the circuit breaker or causes the compressor to short cycle.

To avoid this, make sure you regularly change your system’s air filter for optimal performance. Ideally, you should change the filter at least every two or three months. Change it more if you have pets or the area where your HVAC system is located is particularly dusty.

2. Improper Unit Sizing

An HVAC unit should be properly sized for the space it’s serving. If the unit is too big, it will turn on and off more quickly than necessary, leading to short cycling. Conversely, if the unit is too small, it won’t be able to keep up with demand and may short cycle as a result.

In either case, getting a new, properly sized HVAC unit is the best solution. A professional contractor can help you determine the most suitable size for your home.

3. Frozen Evaporator Coils

If the evaporator coils in your air conditioner are frozen, it can cause the system to shut down. The solution to this problem is to turn off the system for a while and let the coils thaw out. Then, check for any signs of blocked airflow and clear the blockage if necessary. If the problem persists, contact an HVAC technician to inspect your system for any other underlying issues.

4. Low Refrigerant

Refrigerant is a key component of an air conditioner. If the refrigerant level is too low, it can cause the compressor to short cycle. Low refrigerant levels can be caused by leaks in the system or simply running out due to age.

If you suspect a refrigerant leak, contact a trusted HVAC repair professional to inspect the system and resolve the problem at its source. If there isn’t a leak, the tech can recharge the system with refrigerant to get it back up to optimal levels.

5. Thermostat Miscalibration

A well-calibrated thermostat should sense a space’s temperature and turn it off when it’s reached. However, if the thermostat is miscalibrated, it will think that the room has cooled down before it actually has, causing it to shut off.

This is often caused by incorrect wiring within the unit itself or a malfunctioning sensor inside the thermostat. To fix it, you’ll need to call an experienced HVAC technician to calibrate the thermostat and ensure everything is wired correctly.

6. Bad Contactor

The contactors inside an HVAC system act as switches and help the compressor turn on and off. If one of them is bad, the compressor may short cycle as it struggles to reach its target temperature.

The best way to fix this problem is by replacing the faulty contactor. However, this isn’t a DIY job. You’ll need to call a professional HVAC technician to inspect your system and identify the bad contactor before replacing it.

7. Leaky Ductwork

If your HVAC system’s ductwork is leaking, it can cause an imbalance in the pressure of the air being pushed out from the compressor. This imbalance can lead to short cycling, forcing the compressor to turn on and off more frequently than necessary.

The solution here is to locate and seal any leaks in the ductwork before they cause more problems. This requires specialized tools and knowledge, so it’s best to call an HVAC professional who can get the job done quickly and efficiently.

8. Clogged Condensate Drain

As an air conditioner runs, it collects moisture as condensation, which must be drained away from the system. If this drain is clogged, the moisture can build up and lead to a frozen coil. That, in turn, can cause short cycling.

An HVAC technician can check for a clog in the condensate drain line by disconnecting it from the system and inspecting the end of the line. If there is a blockage, they’ll need to clear it out and reconnect the line, restoring the system to its original performance.

9. Defective Relay Switch

The relay switch inside an HVAC system helps to control the flow of current to the compressor. If it’s defective, the compressor may short cycle as it will struggle to turn on and off correctly.

A professional HVAC technician can inspect your system for a faulty relay switch and replace it if necessary. This is usually done by removing the old relay switch and installing a new one.

10. Blocked Outdoor Unit

An HVAC system’s outdoor unit needs space to vent the heat in the refrigerant. The unit can be blocked by debris or dirt, leading to overheating, which causes the system to shut off. This can happen when leaves and twigs have been left to accumulate around the unit for too long.

To fix this issue, clear away any debris or dirt from the outdoor unit and make sure it’s unobstructed. This can be done with a leaf blower or by hand if necessary. If the issue persists, another underlying problem may be to blame, and you’ll need to contact an HVAC technician for further advice.

11. Low Voltage

If there isn’t enough voltage being supplied to the compressor, it can cause it to short cycle. This can be caused by either an issue with the wiring or a problem with the power source itself, such as a faulty fuse or breaker.

When your HVAC technician suspects low voltage, they usually check the wiring and power source to determine the cause. If the problem lies with the wiring, they can repair it or replace it as necessary. For problems with the power source, they may need to install a new fuse or breaker to get your system running again.

Short cycling can cause a host of problems for your HVAC system, so it’s important to identify and resolve the underlying issue as soon as possible. In most cases, however, you’ll need to call a professional HVAC technician who can accurately diagnose the problem and provide an effective solution.

Our HVAC technicians have served the Tampa area with trusted cooling, heating, indoor air quality solutions, duct cleaning, and solar services for over 30 years. We’re here to help get your system running at peak efficiency. If you’re concerned about short cycling in your HVAC unit, contact Air 24/7 Air Conditioning & Heating for assistance.

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