Dehumidifier Compressor Not Running: Causes and Fixes

What stops a compressor from starting

A dehumidifier's compressor is the heart of the moisture removal system. When it stops running, the unit may still blow air but it won't remove humidity. There are three main reasons: the compressor's thermal overload protection has tripped, the start relay has failed, or the control settings are preventing it from running. In many cases, the fix is simple and you can do it without opening the unit.

Thermal overload is a safety feature. When the compressor gets too hot, a bimetallic switch inside the overload protector opens the electrical circuit, cutting power to the motor until it cools down. This can be triggered by running the unit in a very warm room, by a blocked air intake, or by a failing motor. The start relay, meanwhile, gives the motor an extra kick at startup. If that relay is worn out, the compressor may hum but never actually start. And your control panel could be holding the compressor off if the humidity setpoint is too high, or if a timer or mode like "fan only" is engaged.

Before you troubleshoot any internal parts, rule out external factors. Check the power cord and outlet. Make sure the bucket is seated correctly and the float switch is not stuck. Some units will not run the compressor if the bucket is not in place. Refer to Dehumidifier Won't Turn On for a broader startup checklist.

Thermal overload: why it happens and how to reset

Thermal overload is the most common reason a compressor stops on its own. The compressor motor is protected by a thermal overload protector, which is a small device that opens the circuit if the motor temperature exceeds a safe limit. This is a normal protective action, not necessarily a sign of a breakdown. The unit may restart automatically after it cools down, which can take 15 to 30 minutes, but the exact reset time varies by model.

What causes the compressor to overheat? Often, it is running in an unusually hot space. If the air around the dehumidifier is above the recommended operating range, the compressor has to work harder to condense moisture. Another cause is restricted airflow. If the air filter is clogged or the intake is blocked, the condenser coil cannot shed heat, and the compressor temperature rises. A dirty coil can have the same effect.

To reset the overload, turn off the unit and unplug it. Wait for the compressor to cool down completely. In most cases, the thermal protector will reset itself once the temperature falls. If the compressor still does not start after a few hours, the overload protector itself may be defective, or the motor may be drawing too much current. In that case, you may need to have a technician check the motor windings.

Preventing overload starts with keeping the air filter clean and giving the unit plenty of clearance around its intake and exhaust. The EPA notes that the key to mold control is moisture control, and a dehumidifier that cannot run properly will leave you with excess moisture. Follow the maintenance steps in Dehumidifier Filter Maintenance and Where to Place a Dehumidifier for Best Results to keep airflow unrestricted.

Start relay: the common failure that prevents startup

The start relay (or start capacitor and relay assembly) provides the extra voltage needed to start the compressor motor. When the relay fails, the compressor may hum for a second and then go silent, or it may never attempt to start. A relay can fail due to age, electrical surges, or prolonged thermal stress. It is a small, inexpensive part, but opening the sealed refrigeration system is not something most homeowners should do without training.

How to tell if the relay is the problem: If the fan runs but the compressor does not come on at all, and you have already reset the thermal overload and checked the controls, the relay is a likely suspect. You may hear a clicking sound when the unit tries to start. Some relays are located near the compressor on the side of the unit and can be visually inspected for burn marks or a swollen capacitor.

Replacing a start relay requires disconnecting the electrical components and often removing the cover that protects the compressor. If you are not comfortable with electrical work, call a professional. If you do decide to replace it yourself, turn off and unplug the dehumidifier first. The new relay must match the original part number, as the wrong rating can damage the compressor.

Newer dehumidifiers may use a solid-state starting circuit instead of a relay. These can also fail, but they are even harder to diagnose without a meter. If your unit is still under warranty, check the warranty coverage before opening it up. See Dehumidifier Warranties for what to look for.

Control settings that keep the compressor off

Sometimes the compressor is fine, but the control settings tell it to stay off. The most common cause is a humidity setpoint that is higher than the current room humidity. If you set the dehumidifier to 60% and the room is already at 50%, the compressor will not run. Lower the setpoint or use the continuous mode. The CDC recommends keeping indoor humidity below 50% to prevent mold, so a setpoint around 45% is reasonable.

Other settings to check: timer functions may have turned the compressor off after a certain number of hours, even if the fan continues. Some units have a "fan only" mode. If the display shows a fan icon, you may be in that mode. Also, some dehumidifiers have a "dry clothes" or "turbo" mode that changes compressor behavior. Read your owner's manual, or see Humidity Setpoints by Room for guidance.

Another control-related issue is the compressor delay feature. Many modern units introduce a 3- to 5-minute delay before restarting the compressor after it has cycled off, to protect it. If you just turned the unit on after it was running, you may need to wait a few minutes. This is normal. If the compressor still does not start after the delay, check other causes.

If your unit has a digital display, try resetting it by turning the unit off and on, or unplugging it for a few minutes. Some error codes can be cleared with a reset. See How to Reset a Dehumidifier for common reset procedures.

Low temperature and defrost mode

Many compressors stop running when the air temperature is too cold. According to ENERGY STAR, frost can form on the condensing coils when the air temperature drops below 65°F, and this frost can cause the compressor to cycle on and off repeatedly without removing moisture. Some units have an anti-frost sensor that shuts the unit off entirely below a certain temperature.

If your dehumidifier is in an unheated basement or garage, a compressor-based unit may simply not run reliably during the cold months. The compressor may start briefly, then shut off as frost builds on the coils. The unit's defrost cycle is designed to handle this. Some models use a hot-gas valve to warm the coils periodically. For more on defrost behavior, see What Is Auto Defrost on a Dehumidifier and Why It Is Important.

If you are seeing the compressor rarely running in a cool space, the best fix is to look for a dehumidifier rated for low temperature. Some desiccant dehumidifiers work well in cold spaces because they do not use a compressor at all. The choice between compressor and desiccant depends on your climate. See Compressor vs Desiccant Dehumidifiers for Cold Rooms and What Is an LGR Dehumidifier and When Do You Need One for more.

Other common causes to rule out

Before you suspect the compressor itself, confirm that the unit has power and that the fan is actually running. If the fan is not spinning at all, the problem may be with the fan motor, not the compressor. See Dehumidifier Fan Not Spinning. A full bucket or a stuck float switch can also cut power to the compressor. The bucket-full shutoff is designed to prevent overflow, and it isolates the compressor. Empty the bucket and make sure the float moves freely.

A tripped circuit breaker or a dead outlet is another possibility. If the unit was plugged into a ground fault circuit interrupter (GFCI) outlet and it tripped, the compressor will not run. Reset the GFCI and see if the unit starts. If the compressor still does not run, and the unit is less than a few years old, the problem could be a failed compressor motor, which is not worth repairing on most portable units. At that point, consider a new model. Our guides, such as Best 50 to 99 Pints Dehumidifiers in 2026 or Best Basement Dehumidifiers 2026, list models that are known for reliable compressor operation.

What to pick for your use

Questions

Why is my dehumidifier fan running but the compressor is not?

This is typically caused by a tripped thermal overload, a failed start relay, or a control setting like a high humidity setpoint or timer. Check the setpoint first, then wait for the compressor to cool down if it was overheated. If neither works, the relay may need replacing.

How long does it take for a dehumidifier compressor to reset?

Most thermal overload protectors reset within 15 to 30 minutes after the compressor cools down. If the compressor does not start after a few hours, the overload protector itself may be faulty, or there may be another issue.

Can low temperature cause a dehumidifier compressor to not start?

Yes. According to ENERGY STAR, frost can form on the condensing coils when the air temperature drops below 65°F, which can cause the compressor to cycle on and off or shut down. Some units have an anti-frost sensor that stops the compressor.

How do I know if the start relay is bad?

If the fan runs but the compressor hums or does not start at all, and the thermal overload is not the issue, the start relay is a likely suspect. You may hear a click when the relay tries to engage. A visual inspection for burn marks or a swollen capacitor can help, but replacement usually requires professional help.

Can a dirty air filter prevent the compressor from running?

Yes. A clogged filter restricts airflow, causing the condenser to overheat and the thermal overload to trip. Cleaning or replacing the air filter is a simple first step. See our filter maintenance guide for details.

Should I try to repair the compressor myself?

If you have experience with electrical appliances and the compressor is not the part that is faulty, you can replace the relay or capacitor. But if the compressor motor itself is dead, it is usually more cost-effective to buy a new dehumidifier. Always unplug the unit before opening it.

What humidity setting should I use to keep the compressor running?

Set the dehumidifier to a lower value than the current room humidity. The CDC recommends keeping indoor humidity below 50% to prevent mold. If the room is already below your setpoint, the compressor will not run, so lower the setpoint to force it on.

Is it worth replacing a relay on an old dehumidifier?

If the unit is only a few years old and in good condition, replacing a relay can be a cheap fix. But if the compressor has other issues, such as noisy operation or weak cooling, it may be time to consider a new model. Check your warranty first.