If your HVAC system is turning on and off repeatedly in short bursts, without improving the temperatures, it might be short cycling.
Most of the time, this has to do with low batteries or loose connections on the thermostat.
However, it can also indicate an underlying issue with the rest of the HVAC system. So in this guide, I’ll walk you through 12 of the most common reasons for short cycling. Let’s go!
What is Short Cycling?
Short cycling is a phenomenon that happens when an air conditioning or heating system is unable to complete a full cooling cycle.
A complete cooling cycle starts when the air conditioner turns on and ends when the thermostat's set temperature is reached, and the unit turns off again.
When a system is short cycling, it can’t achieve a comfortable temperature since the system switches on and off repeatedly without improving the temperatures.
This not only increases energy consumption, leading to higher bills, but it also puts unnecessary strain on the system, causing your filters and equipment to wear down faster.
How To Confirm If Your System is Short Cycling?
Here's how to confirm if your system is experiencing short cycling:
- Switching on and off intermittently: If either your AC or furnace keeps turning on and off repeatedly within a short time frame (in minutes or even mere seconds).
- Keeps running more frequently than usual: Your AC or furnace might be running more often than what you consider normal.
- The system can’t attain the setpoint temperature: Your system is struggling to achieve the setpoint (adjusted) temperature and it takes hours to make a noticeable difference.
- Equipment Turns On Even When the Temperatures are Stabilized: If you haven't altered the temperature settings in your house, and your AC or furnace turns on and off trying to meet a demand you haven't made.
What are the Long-Term Issues with Short Cycling?
Long-term issues with short cycling can lead to increased energy consumption, higher electric bills, and excessive wear on your thermostat and HVAC system.
This extra strain can result in premature component failure and higher maintenance costs, while also negatively impacting the overall comfort of your living space.
Also, the system might not be able to achieve comfortable temperatures since it’s constantly short cycling.
Compressor Protection Feature
The compressor protection feature allows the smart thermostat to prevent the compressor from starting up for a brief moment, safeguarding it from potential damage.
When engaged, the thermostat screen displays “Waiting for Equipment,” or on older models, you may see “Wait,” a flashing “Cool On,” or “Heat On” message.
This feature can help minimize short cycling but only when the system is recovering from a power outage or when the temperature is adjusted manually or via the schedule.
If the “Waiting for Equipment” message persists longer than five minutes, there may be an underlying issue present.
In that case, check out this guide for more information.
Reasons for Short Cycling
There can be several reasons why your HVAC System is short-cycling. It can be due to an issue with the thermostat or the rest of the HVAC system.
First, we'll get into the thermostat and then start tackling the rest of the system.
At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if, in any doubt, it is best to seek the assistance of a professional.
Reason 1. Thermostat Running Out of Batteries
When a Honeywell thermostat's batteries are running low, you will be notified in advance or you may experience screen flickering or glitches.
Because of low batteries, the thermostat might be floating in and out of the system, sending signals intermittently to the heating or cooling equipment.
Therefore, replacing the batteries as soon as possible can help prevent short cycling and maintain the thermostat in optimal condition.
Reason 2. Loose Connections in the Thermostat
Loose connections within a thermostat can lead to short cycling in heating and cooling systems.
To tackle this issue, take out the thermostat from the wall mount and inspect the wiring strip and terminal block to make sure all contacts are secured firmly.
If possible, try removing the wires from the contacts and reinstalling them for good measure. Make sure you have the proper tools and clean the contacts from any dust or debris.
Also, make sure the wiring configuration is correct, with the wires neatly aligned to their corresponding contacts.
James from One Hour Smart Home has a great video on this here.
Additionally, check the thermostat strip on your furnace's control board and confirm the wire connections there are secure as well.
Reason 3. Low Voltage in the Thermostat
Wiring issues can result in reduced voltage, specifically among the R and C wires which provide 24V AC power to your thermostat (for models that don’t run on batteries or use them for emergencies only).
It is essential to test the incoming voltage to ensure your thermostat receives the required 24-30V AC power.
If you have a multimeter and you’re comfortable checking the voltage from the thermostat contacts, you can try this out yourself. Otherwise, it’s best to get help from a professional.
Reason 4. Faulty Indoor Temperature Sensor
Although rare, the indoor temperature sensor in your Honeywell smart thermostat can malfunction or take incorrect measurements, leading to short cycling.
To determine if the sensor is the issue, compare the thermostat's temperature reading with that of a separate thermometer.
If there's a discrepancy between the two readings, your sensor might be to blame.
Placement of the Thermostat
Another potential cause of inaccurate temperature readings is the placement of air vents, windows, or any other equipment (such as computers, or air fryers) that can change the temperature in the immediate area surrounding the thermostat.
This equipment and fixtures can cause the internal temperature sensor to be measured inaccurately, causing short cycling with the thermostat and sending the wrong signals to the rest of the HVAC equipment.
Moving a thermostat to a different location is not the best course of action. Instead, I recommend moving the equipment or blocking the vents that are within the thermostat's immediate vicinity.
Bypassing the Thermostat
To further investigate, you can try bypassing the thermostat entirely. If your furnace or AC runs without short cycling in this scenario, it's definitely the thermostat that’s causing all these issues.
Beyond that, you can try resetting the thermostat.
Reason 5. Clogged Air Filters or Blocked Vents
Restricted airflow into your furnace or HVAC system can cause the temperature and pressure sensors in your HVAC system to toggle on and off repeatedly.
To avoid this problem, change or clean your filters regularly.
Blocked vents can also contribute to this, so when dust, debris, or foreign objects block the intake or return vents, only a fraction of the air can enter your furnace or system.
It's important to check for any obstructions in your vents and remove them as needed.
Reason 6. Dirty Evaporator Coil/ A Coil
A dirty evaporator coil can cause short cycling due to dust accumulation, which restricts airflow, creates low pressure in the refrigerant, and trips the low-pressure switch.
To resolve this issue, clean the coil yourself or get a professional to do it. Also, consider having your ducts cleaned as well.
Reason 7. Low on Refrigerant/ Refrigerant Leak
A refrigerant leak or low levels of refrigerant in your Honeywell thermostat can lead to short cycling.
- In this situation, short cycling occurs when the low-pressure switch shuts off the system when it detects low refrigerant.
- After that, the switch automatically resets when the pressure on the low-pressure side of your refrigeration system returns to normal.
- If there’s a leak or an issue with the compressor, the pressure will stabilize near the sensor again, causing it to run in an endless loop.
- As a result, this creates a short cycling condition.
Topping up the refrigerant from time to time is only a temporary solution so it’s a good idea to address the leak or any other underlying issues with the help of a professional.
Reason 8. Oversized HVAC System
An oversized HVAC system can lead to short cycling issues with your Honeywell thermostat.
- When an AC is too powerful for a home, it cools the area rapidly and unevenly, preventing proper humidity absorption.
- This rapid cooling disrupts the thermostat's ability to maintain a constant temperature, causing the furnace to continuously turn on and off in an effort to reach the desired setting.
To resolve this issue, you can try reducing the blower speed fan, which will decrease the cooling speed and allow the system to run longer, which can help cool the house more evenly.
However, for a more accurate and long-term solution, it's best to consult with a professional HVAC company to perform a heat load calculation and get advice on how to optimize the system.
Reason 9. Dirty or Damaged Flame Sensor
A dirty or damaged flame sensor presents a significant problem as it can directly contribute to your Honeywell smart thermostat's short cycling.
This not only impacts your home's comfort but also affects its efficiency, leading to increased energy consumption and costs.
- To address this issue, it's important to regularly inspect and clean your flame sensor.
- A clean sensor ensures that it functions optimally and detects flames accurately.
- However, if cleaning the sensor doesn't fix the short cycling issue, it may be time to replace it.
- So replace it yourself or consult an HVAC professional if you're unsure about handling the equipment yourself.
Reason 10. Bad Contactor Relay on the Compressor
A bad contactor relay on the compressor can lead to Honeywell thermostat short cycling, as it might be faulty or the contacts might be dirty or blocked.
If possible, you can try checking the voltage on the contactor. You should get 24V AC to ensure it's receiving adequate power.
If you encounter any issues, I highly recommend replacing it or getting an HVAC technician to take a look.
Reason 11. Partially Clogged Drain Line
When the drain line, is clogged up, the air conditioner's float switch – responsible for monitoring possible clogs – turns off the system to prevent overflow and potential leaks.
So if the drain line becomes partially clogged, it might trigger the float switch unnecessarily, resulting in your air conditioner short cycling.
If you find this to be the issue, make sure to unclog the drain pipe using a wet/dry vacuum, drain cleaner, or a tool such as a plumber's snake.
Reason 12. Compressor That’s Failing to Start
Another common example of short cycling is when the fan activates, but the compressor only hums for a few seconds before shutting off.
There can be several reasons but the most being that the compressor is failing to start.
To remedy this, you can try replacing the dual-run capacitor or installing a hard start kit.
However, it could also be an underlying issue with your compressor. In this case, it's crucial to contact a qualified HVAC technician for further assistance.
Apart from the ones mentioned above, there can be several other reasons why your smart or non-smart thermostat is short cycling:
- Damaged Transformer
- Power Fluctuations
- Faulty Control Boards
- Electrical Short
- Bad Condenser Fan Motor
- Dirty Evaporator Coil
- Higher Cycle Rate in Thermostat
If possible, try rectifying these yourself, waiting it out, or getting help from a professional.
As you can see there are more than a dozen reasons why short cycling might occur in your HVAC system. However, most of the time, replacing the batteries or bypassing the thermostat can help you get a firm idea of why this is happening.
So if your thermostat isn’t to blame, it might be your heating or cooling system. If which case, I highly recommend getting the help of a professional.