The AprilAire 4655 is a mechanical humidistat designed to regulate indoor humidity levels in residential environments. It is compatible with a wide range of AprilAire humidifier models and is used to control both evaporative and steam humidification systems. As a manual control, it does not rely on digital programming or automation, making it a simple and reliable option for homeowners seeking to maintain optimal indoor air quality.
This article provides a comprehensive overview of the installation process, key specifications, and operation of the AprilAire 4655, based on the manufacturer’s documentation and supporting technical data. It is intended to assist U.S. consumers, DIY enthusiasts, and HVAC professionals in understanding how to properly install and use this humidistat.
Key Specifications and Compatibility
The AprilAire 4655 is a wall-mountable humidistat that operates on a 24 VAC power supply, making it compatible with most residential HVAC systems. It uses a mechanical filament to detect changes in relative humidity (RH), which in turn controls the humidifier’s operation by opening or closing a dry-contact switch.
The humidistat has a humidity setting range of 15% to 50% relative humidity, with an operating differential of approximately 8%. This means that once the desired humidity level is reached, the humidifier will stop operating until the humidity drops by about 8%. The 4655 also supports a maximum load of 5.2 amps, suitable for most residential humidification systems.
The device is compatible with a wide range of AprilAire humidifier models, including:
- 400M, 400MK, 400MZ, 400MKZ
- 500M, 500MK, 500MZ, 500MKZ
- 600M, 600MK, 600MZ, 600MKZ
- 620M
- 700M, 700MZ, 700MKZ
- 720M, 720MKZ
These models include both evaporative and steam humidifiers, and the 4655 is designed to work with either type. The humidistat is also compatible with various AprilAire humidifier accessories and components, such as the 110 Fan-Powered Humidifier, 350 Humidifier Parts, and several 700- and 1100-series units.
Installation Process
The AprilAire 4655 can be installed in two primary ways: wall-mounted or mounted on a return air duct. Both methods require access to a 24 VAC circuit and proper placement to ensure accurate humidity readings.
Mounting Options
Wall Mounting: The humidistat can be mounted on a living space wall. This option is ideal for homes where the HVAC system is not easily accessible or where the homeowner prefers to control humidity from a central location.
Return Duct Mounting: This method involves mounting the device directly on a return air duct. This is generally preferred by HVAC technicians because it allows the humidistat to sample the air in the duct, which is typically more stable and representative of the overall indoor environment.
In both cases, the device must be installed on a dry, non-corrosive surface. It is recommended that the humidistat be placed in a location free from direct heat sources, drafts, or areas with high moisture levels, as these can affect the accuracy of the humidity readings.
Included Components
The 4655 installation kit includes the following items:
- One (1) wall-mount humidistat
- One (1) installation manual
- One (1) safety and installation instructions sheet
- One (1) wiring recommendation sheet
- Two (2) drywall anchors
- Two (2) mounting screws
- One (1) gasket
The gasket is used to create a tight seal between the humidistat and the mounting surface, preventing air leaks that could affect humidity readings. The mounting hardware is suitable for most drywall or duct surfaces, and the installation manual provides step-by-step guidance for proper setup.
Electrical Requirements
The AprilAire 4655 is a 24 VAC control device, meaning it requires a low-voltage power source typically provided by the home’s HVAC system. It does not require a separate power supply and is wired in parallel with the humidifier and HVAC system.
It is important to verify that the humidifier system is receiving power and that the water supply valve is open before testing the device. The humidistat does not provide power to the humidifier itself but rather acts as a switch that closes the circuit when humidity levels drop below the set point.
Safety and Compliance
The AprilAire 4655 is designed and manufactured in the United States and is backed by a 5-year limited warranty. The warranty covers defects in materials and workmanship and requires registration via the manufacturer’s website or by mail. The device is also compliant with all relevant U.S. safety and electrical codes for residential HVAC controls.
Operation and Maintenance
Once installed, the AprilAire 4655 functions by opening and closing a dry-contact switch in response to changes in humidity. When the relative humidity in the space drops below the set point, the nylon filament inside the device contracts, closing the switch and allowing the humidifier to operate. When humidity rises to the desired level, the filament expands, opening the switch and stopping the humidifier.
The device does not require digital configuration or programming. Instead, the user sets the desired humidity level using a physical knob. The humidistat is typically set to a level between 40% and 50% RH, which is considered optimal for most indoor environments.
Initial Setup
For first-time installation, the manufacturer recommends setting the humidistat to a setting of 5 during the first heating season. This allows the system to adjust to the home’s environment and may require minor adjustments during the coldest part of the season. Once the system is calibrated, the humidistat should maintain the desired humidity level with minimal intervention.
Indicator Lights (Digital Models)
While the 4655 is a manual model, some digital versions of the humidistat include indicator lights that provide visual feedback on system status. These lights include:
- Green Light: Indicates normal operation
- Yellow Light: Indicates that the water panel needs to be changed (only applicable to certain models)
- Red Light: Indicates that service is required
The 4655 manual model does not include these lights, but the digital model is available for users who prefer additional feedback and control options.
Annual Shutdown
During the summer months, it is recommended to shut down the humidifier system to prevent mold growth and water wastage. For the AprilAire 4655, this involves setting the humidistat to the “OFF” position and ensuring that the water supply is turned off.
The process varies slightly depending on whether the humidistat is in automatic or manual mode:
- Digital Control in Automatic Mode (Blower Activation Off): No adjustment is necessary.
- Digital Control in Automatic Mode (Blower Activation On): Set the knob to the OFF position.
- Digital Control in Manual Mode: Set the knob to the OFF position.
- Manual Humidistat: Set the knob to the OFF position.
This step helps preserve the humidifier and ensures that it is ready for use at the start of the next heating season.
Troubleshooting
If the humidifier fails to operate or the humidity level does not stabilize, the following steps can be taken:
- Verify Power Supply: Ensure that the HVAC system is powered on and that the humidifier is receiving electricity.
- Check Water Supply: Confirm that the water saddle valve is open and that there is no blockage in the water line.
- Inspect Humidistat Settings: Ensure that the humidistat is set to the correct humidity level and that the control switch is not stuck or damaged.
- Test Humidifier: If the humidifier still does not operate, the solenoid valve or water panel may need to be inspected or replaced.
If these steps do not resolve the issue, it is recommended to contact a qualified HVAC technician or AprilAire customer support for further assistance.
Warranty and Support
The AprilAire 4655 is backed by a 5-year limited warranty that covers defects in materials and workmanship. To register the product, users can either complete the online registration form on the AprilAire website or mail a postcard with the product details to the manufacturer’s address in Madison, Wisconsin.
The warranty does not cover damage caused by improper installation, misuse, or modifications to the device. It is important to follow the manufacturer’s installation and maintenance guidelines to ensure that the product remains covered.
For technical support, users can visit the AprilAire website or call the company’s toll-free number at 800-334-6011. The website also provides digital copies of the product manual, warranty information, and frequently asked questions (FAQs) that may be helpful for troubleshooting.
Conclusion
The AprilAire 4655 is a reliable and user-friendly manual humidistat designed for residential use. It offers a simple and effective way to regulate indoor humidity levels without the need for digital controls or programming. With a 5-year warranty and compatibility with a wide range of AprilAire humidifiers, it is an excellent choice for homeowners looking to improve indoor air quality.
Installation is straightforward, with the device available in both wall-mount and return duct mount options. The included mounting hardware and installation manual make it easy for DIY users or HVAC professionals to complete the setup. Once installed, the 4655 provides accurate humidity control using a mechanical filament, ensuring consistent performance throughout the heating season.
Regular maintenance, including annual summer shutdown and periodic inspection of the water supply and humidifier components, helps ensure the device continues to function effectively. If issues arise, the manufacturer provides warranty support and technical assistance to help resolve any problems.
For homeowners and HVAC professionals seeking a dependable, cost-effective solution for residential humidity control, the AprilAire 4655 offers a proven and reliable option.