By SunTouch® - A Division of Watts Water Technologies, Inc.
Installation Guide
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General Safety Instructions 1. This unit should be installed, opened, and serviced only by qualified personnel. 2. To avoid electrical shock, do not open the front cover while power is connected to the PM-824 or any controlled equipment. 3. Limit input voltage to 22-28 VAC/VDC. 4. Replace fuse F1 only with a 2 Amp, 32V or 250V, 3AG fast-acting fuse. |
Moisture Sensor Mounting & Termination
The remote PM-824 precipitation and moisture sensor may be mounted in several different ways depending on the application and installation environment.
Proper sensor placement is important for accurate snow and ice detection and reliable snow melting system operation.
The PM-824 operates on safe 24 VAC/VDC power and is designed to withstand outdoor weather conditions, including temporary water immersion.
For roof and gutter deicing applications, the sensor head may be mounted inside the gutter against the fascia board using a 1-inch C-style conduit clamp.
Allow part of the sensor grid to remain exposed to snowfall. This allows the sensor to activate when snow begins falling and remain active while melted snow continues dripping from the roof edge during freezing conditions.
The sensor may also be mounted near the top of a downspout using a 1-inch conduit hanger and mounting plate.
As melted water flows through the gutter and downspout, the moisture reaching the sensor helps maintain proper system activation.
Do not lay the sensor directly in the gutter.
Constant water immersion may corrode the precipitation grid and reduce detection reliability during windblown snow conditions.
The sensor cable is pre-installed but may be shortened if necessary.
Strip the outer insulation and shielding carefully, then terminate each conductor according to the color code printed on the circuit board.
The bare drain wire must be connected to the terminal labeled “Shield”.
Secure a cable tie around the cable inside the enclosure to provide strain relief between the enclosure gland and the cable connection.
If additional cable length is required, contact the manufacturer for proper extension recommendations. Incorrect cable types may result in erratic system operation.
Selecting a Mounting Location for the PM-824 Enclosure
The rubber boot extending from the bottom of the PM-824 enclosure contains the temperature sensor.
For accurate temperature detection, the PM-824 must be mounted outdoors away from furnace vents, dryer vents, or other artificial heat sources.
When powered, the PM-824 precipitation grid will remain warm during operation. This is normal and helps continuously melt snow and evaporate moisture from the sensor grid.
Power & Activation Indicator
A yellow indicator lamp located on the base of the PM-824 displays operational status.
- If the lamp is OFF, the PM-824 is not receiving power
- If the lamp remains steadily ON, the PM-824 is powered but not activated
- If the lamp is FLASHING, the PM-824 has activated the snow melting system
Even after snowfall stops, the indicator may continue flashing while the Delay-Off drying cycle remains active.
Preseason Snow Detection Testing
Testing the PM-824 before the winter season is strongly recommended.
To perform a test, use clean water and, if outdoor temperatures are above the activation point, a can of electronic component cooler spray.
Clean the precipitation grid and allow it to dry completely before testing.
Apply power to the PM-824 and drip water onto the precipitation grid. Spray the temperature sensor with the component cooler until the activation temperature is reached.
Once both moisture and temperature conditions are met, the PM-824 should activate and the internal relay should engage.
After testing, allow the precipitation grid to dry completely.
To clear the Delay-Off timer, place the override switch into the “Standby/Reset” position and then return it to “Automatic”.
Need Indoor Monitoring & Control?
The optional PM-DP display panel provides convenient indoor monitoring and control compatibility for the PM-824 snow melting controller system.
The PM-DP offers simple installation, easy operation, and quick visual confirmation of snow melting system activity.
Fine Adjustment for Efficient Operation
The PM-824 is factory preset with the TEMP and DEL adjustments centered at approximately 39°F (3.9°C) and 30 minutes of Delay-Off time.
The sensitivity control is preset to maximum sensitivity.
Depending on local weather conditions and installation environment, fine adjustment may improve performance and operating efficiency.
- Increase the trigger temperature if the sensor does not activate during wet snowfall conditions
- Lower the trigger temperature if unwanted activation occurs during cold rain conditions that do not freeze
- Reduce sensitivity in areas exposed to blowing snow or snow falling from roofs and trees
- Adjust the Delay-Off cycle to improve melt-off performance while reducing unnecessary run time
Always make adjustments in small increments to maintain reliable system operation.
Use care when reinstalling the enclosure front cover.
Ensure the gasket is properly seated and not pinched or rolled. Do not overtighten the cover screws.
Manual Override Switch Operation
An override switch located on the side of the PM-824 provides additional operating and testing functions.
- Automatic: Allows normal sensor-controlled operation
- Manual On: Activates the controlled equipment manually
- Standby/Reset: Prevents activation, clears active delay timers, and opens the load relay
To prevent excessive operating time, Manual On mode automatically returns to Automatic mode after approximately 40 hours, even if the switch remains in the Manual On position.
To restart Manual On operation, switch the unit back to Automatic and then return it to Manual On.
If the override switch is placed into Manual On for less than two seconds and then returned to Automatic, the controller will execute a single Delay-Off cycle.
This feature can help clear frost or hail buildup without leaving the system continuously energized.
The Standby/Reset position may still be used to cancel the Delay-Off cycle.
External Control & Monitoring Operation
An external control and monitoring jack is included on the PM-824 controller.
The optional CS-1 control and monitor cable may be used to access these functions.
- Connecting Black to White activates Manual On mode
- Connecting Green to White activates Standby/Reset mode
- The Red and Orange leads connect to the internal monitoring relay
The internal monitor relay is rated for 24 VAC/VDC at 400 mA and closes together with the load relay for external monitoring applications.
| Pin | Color | Function |
| 1 | Green | Standby/Reset |
| 2 | Black | Manual On |
| 3 | Orange | Deice On Monitor |
| 4 | Red | Deice On Monitor |
| 5 | White | Return |
Precipitation Grid Maintenance & Replacement
It is recommended that the PM-824 be powered down and the precipitation grid cleaned with clear water at least once every four months.
Heavy buildup may be removed using a non-metallic scouring pad such as Scotch-Brite or an equivalent product.
Over time, minerals and corrosive elements left behind from evaporated moisture may eventually damage the precipitation grid rings.
The precipitation grid can be replaced by installing a new MG-3 Moisture Grid Assembly.
Refer to the Moisture Sensor Mounting & Termination section for additional replacement information.
The PM-824 enclosure may be mounted using the base conduit hub attached to a properly sized freestanding conduit or by using the mounting holes located in each corner of the enclosure.
Do not drill holes through the enclosure for mounting.
Drilling through the enclosure may allow water intrusion and create potential electrical shock or fire hazards.
A weatherproof conduit body or junction box should be installed below the PM-824 enclosure for safe termination of power and load wiring connections.
Always use care when reinstalling the enclosure front cover.
Ensure the front cover gasket is properly seated and not pinched or rolled. Do not overtighten the cover screws.
Setting the Configuration Switches and Adjustments
The PM-824 includes several adjustable operating modes and configuration settings for customizing snow melting system performance.
The Trigger Temperature (TT) can be adjusted from 34°F to 44°F using the Temperature Adjust control.
When ambient air temperature falls below the trigger temperature, precipitation is interpreted as snow. When temperatures remain above the trigger point, precipitation is treated as rain.
- The SNOW switch activates the controller during snowfall conditions
- The RAIN switch activates the controller during rainfall conditions
The DEL configuration switch controls the Delay-Off drying cycle timer.
This drying cycle allows the heated surface to continue operating after precipitation stops, helping evaporate remaining moisture and reduce refreezing conditions.
The LD configuration switch controls the Delay-Off timing range:
- LD OFF = 30 to 90 minute range
- LD ON = 2 to 6 hour range
The Delay-Off timer restarts each time new precipitation is detected.
As long as precipitation continues, the PM-824 remains active and then continues operating through the programmed Delay-Off cycle once precipitation ends.
All Sensor Modes provide a two-minute relay closure to reduce cycling of external controllers.
In Controller Mode, Delay-Off timing can be adjusted using the Delay Adjust control.
Use the Forced Manual On area only for testing purposes.
Do not leave the Delay Adjust control near the Forced Manual On range during normal operation.
The Low Temperature Cutoff (LTC) option is commonly used with snow melting systems that have limited heating output capacity.
When enabled, the sensor will not activate if precipitation is initially detected below 15°F.
However, if the system has already activated and precipitation continues while temperatures fall below 15°F, the LTC setting is ignored to prevent refreezing conditions.
This allows melted moisture to continue evaporating safely from the heated surface.
The PM-824 precipitation sensor is sensitive enough to detect very small amounts of snow or rain.
In locations exposed to wind, condensation, or drifting snow, nuisance triggering may occasionally occur.
Proper sensor placement is the best solution, although the Sensitivity control may also be adjusted when necessary.
The highest sensitivity setting requires approximately three seconds of continuous moisture detection before activation.
The lowest sensitivity setting requires approximately four minutes of continuous moisture detection before activation.
Light drifting snow or trace moisture may evaporate before activation occurs at lower sensitivity settings.
For best reliability, begin with the highest sensitivity setting and make small adjustments only as needed.
Power must be cycled for configuration switch changes to take effect.
Recommended Switch Settings by Function
| Function | Trigger | LD Off | LD On | LTC | DEL | RAIN | SNOW |
| Snow Sensor without LTC | TT > AT | 2 Min | 2 Min | OFF | OFF | OFF | ON |
| Snow Sensor with LTC | TT > AT > 15°F | 2 Min | 2 Min | ON | OFF | OFF | ON |
| Snow Controller without LTC | TT > AT | 30-90 Min | 2-6 Hr | OFF | ON | OFF | ON |
| Snow Controller with LTC | TT > AT > 15°F | 30-90 Min | 2-6 Hr | ON | ON | OFF | ON |
| Precipitation Sensor | Not Used | 2 Min | 2 Min | X | OFF | ON | ON |
| Precipitation Controller | Not Used | 30-90 Min | 2-6 Hr | X | ON | ON | ON |
| Rain Sensor | AT > TT | 2 Min | 2 Min | X | OFF | ON | OFF |
| Rain Controller | AT > TT | 30-90 Min | 2-6 Hr | X | ON | ON | OFF |
Typical Wiring
The PM-824 sensor supply voltage operates within a range of 22-28 VAC/VDC.
The supply input leads labeled IN A and IN B are not polarity sensitive and may be connected to either polarity when using a DC power supply.
A standard 24VAC 20VA HVAC-style transformer provides sufficient power for both the PM-824 controller and the optional PM-DP indoor monitoring and control panel.
The PM-824 load leads do not directly supply power to the connected equipment.
Instead, the internal relay functions like a switch or thermostat, allowing the controller to switch a separate voltage source for the connected load.
This design allows the PM-824 to operate on one voltage while controlling equipment operating at a different voltage without requiring an additional relay or contactor.
For example:
- The PM-824 may operate from 24VAC while controlling a 12VDC contactor coil
- The PM-824 may also provide a dry-contact closure for boiler control systems
The following wiring diagrams illustrate several common connection methods for integrating the PM-824 with snow melting equipment.
For clarity, the grounding conductor is not shown in the diagrams.
PM-824 Specifications
| Dimensions | 4¾ in x 7 in x 2¾ in (120 x 178 x 70 mm) |
| Weight | 2 lb (0.9 kg) |
| Configuration Modes | Snow Only / Rain Only / Snow or Rain |
| Delay Settings | 30 to 90 minutes / 2 to 6 hours |
| Low Temperature Cutoff (LTC) | Prevents operation below 15°F ambient temperature |
| Operation Modes | Automatic / Standby-Reset / Manual |
| Operating Temperature | -40°F to +185°F (-40°C to +85°C) |
| Enclosure Rating | NEMA 3R |
| Supply Power | 22-28 VAC/VDC, 15VA maximum, 5VA typical |
| Trigger Temperature | 34°F-44°F (1.1°C-6.6°C) field adjustable |
| Load Contact Capacity | 30A @ 24 VAC, minimum 100,000 operations at full load |
| Monitor Contact Capacity | 24 VAC/VDC, 400mA, 10W total |
Key Features & Benefits
- Designed for low-voltage hydronic and battery-powered systems
- Automatic activation helps reduce deicing operating costs
- Reliable rain and snow detection technology
- 24 VAC/VDC operation with only 20 VA required
- Full 30A @ 24VAC control capacity
- Replaceable remote precipitation sensor
- Easy installation with full access to electronics
- Multiple operating modes in one controller
- Adjustable trigger temperature settings
- Selectable Delay-Off cycle from 30-90 minutes or 2-6 hours
- Adjustable sensitivity control for local weather conditions
- Selectable low-temperature cutoff protection
- Smart Manual-On function for temporary activation cycles
- Professional-grade design for residential and commercial snow melting systems
General Safety Information
Warning: Disconnect all power sources before servicing or installing this equipment.
Installation must comply with all local electrical codes and applicable national electrical standards.
Improper installation may result in property damage, equipment failure, electrical shock, or personal injury.
- Read all instructions completely before beginning installation
- Only qualified personnel should install or service the controller
- Do not energize the system until all wiring has been verified
- Follow all manufacturer recommendations for sensor placement
- Verify voltage compatibility before connecting power
PM-824 Snow & Ice Sensor Controller Overview
The PM-824 controller monitors moisture and temperature conditions to automatically activate connected snow melting systems during snow and ice events.
The controller is commonly used for:
- Snow melting driveways
- Walkways and sidewalks
- Outdoor ramps
- Commercial entrances
- Hydronic snow melting systems
- Electric snow melting systems
The system improves safety while helping reduce unnecessary operating costs by activating only during appropriate weather conditions.
Moisture Sensor Mounting Guidelines
Proper sensor placement is critical for accurate snow and ice detection.
- Install the sensor where snowfall exposure is unobstructed
- Avoid mounting near roof drip lines or artificial heat sources
- Do not install near exhaust vents or dryer outlets
- Position the sensor where snow naturally accumulates
- Ensure the sensor remains accessible for inspection and maintenance
Improper sensor placement may affect snow melting system performance.
Power and System Operation
The PM-824 controller includes visual indicators for monitoring power and activation status.
When moisture and temperature conditions meet activation requirements, the controller automatically energizes the connected snow melting system.
System functions may include:
- Manual override operation
- Adjustable Delay-Off timing
- Adjustable activation temperature settings
- Remote monitoring compatibility
- External control integration
Preseason System Testing
Before winter operation begins, inspect and test the complete snow melting system.
- Verify all wiring connections are secure
- Inspect sensors for debris or damage
- Confirm proper controller operation
- Check system activation functions
- Verify ground fault protection operation
Routine preseason testing helps ensure reliable operation during snow and ice conditions.
Wiring and Configuration
All wiring must comply with local electrical codes and manufacturer installation requirements.
Verify all voltage settings, activation parameters, and configuration switch settings before energizing the system.
Typical configuration adjustments may include:
- Activation temperature settings
- Delay-Off timing adjustments
- Manual override operation
- Sensor sensitivity adjustments
- External monitoring connections
Improper configuration may affect overall system performance and reliability.
PM-824 Controller Specifications
- Automatic snow and ice detection
- Compatible with electric and hydronic systems
- Weather-responsive operation
- Adjustable activation settings
- Designed for outdoor snow melting applications
- Professional-grade installation design
Helpful Resources:
- SunTouch How-To Videos
- SunTouch ProMelt Specifications Guide
- SunTouch ProMelt Installation Manual
- EMF - Electromagnetic Fields Information
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