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Weathermatic SMARTLINE 20 Station Indoor/Outdoor Controller | SL1620

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Free Shipping on Orders over $149
Sale Price $408.43
Our Price $701.89
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20-zone controller with permanently-mounted modules.

Features & Benefits of the SL1620 Controller

  • Internal 120VAC/230VAC transformer with plug and play pre-installed 6' line cord (removable for conduit-wired installations)
  • Four (4) program controller with 20 zones permanently mounted
  • 4-zone hot-swappable modules (Indoor/outdoor rated)
  • Large backlit LCD display
  • 2 run modes: Standard mode runs user input zone run times; Auto Adjust mode requires SLW Series On-Site Weather Station to calculate weather based run times that override user input zone run times
  • Rain/Freeze sensor bypass/active button located on face panel displays sensor status with tri-color LEDs (red indicates sensor is prohibiting irrigation; orange indicates an extended rain delay after weather station rain sensor permits irrigation; green indicates normal operation)
  • 4 programs: A, B, C; program D can operate concurrently
  • 8 start times per program
  • Nonvolatile memory and real time clock/calendar circuit to retain programs as well as correct date and time - with no battery required
  • Zone run times settable from 1 min. to 9 hrs. 55 min. with operation countdown displayed in hours, minutes, and seconds (zone run times overridden by weather based calculated values in Auto Adjust mode)
  • Watering day selections of custom days of the week, odd/even, or interval days
  • Omit settings: omit time of day window, omit day(s) of week, and omit up to 7 calendar dates
  • Seasonal % adjust by program, by month for simple year round water budgeting (monthly percentages overridden in Auto Adjust mode)


  • Input: 120VAC/60Hz @ 400mA for 3 valves
  • Output: 28VAC, 1.0A maximum
  • Fuse: 1.0A, slow blow
  • Dimensions: 9-1/8" W x 10-1/2" H x 4" D (23,2 cm x 25,7 cm x 10,2 cm)

Auto Adjust Features

  • ZIP Code input (5 digit) or Latitude input (+/-60 degrees from EQUATOR) establish location of site for solar radiation calculation
  • Sprinkler type input allows selection for zone sprinkler type (SPRAY, ROTOR, DRIP, BUBBLER) with preset precipitation rate or specific input of the zone precipitation rate (.2 - 3.0" per hour)
  • Plant type input allows selection for zone plant type (COOL TURF, WARM TURF, SHRUBS, ANNUALS, TREES, NATIVE) with preset crop factors or specific input of the zone crop factor (10 - 300%)
  • Soil type input allows selection for the soil type (CLAY, SAND, LOAM) and slope (0 - 25 degrees) for the purpose of automatically calculating a run/soak period to virtually eliminate run off
  • More/Less is settable by zone (-50% to +25%) for the purpose of fine tuning Auto Adjust run times to accommodate factors like shade, wind, and sprinkler inefficiencies

Advanced Functions

  • Fault review displays all faults, including open and shorted zones
  • Diagnostic test function using on-board multi-meter displays transformer voltage; milliamp measurement for each zone
  • Built-in valve locator function for locating hidden valves by simply listening for the audible chatter of the solenoid created by a unique electrical frequency (patent pending)
  • Review menu displays accumulated ET deficits by zone (in inches) and corresponding zone run times for the next available watering day
  • Review menu displays maximum run time and minimum soak time used during Auto Adjust mode
  • Review menu displays temperature readings (daily high/low) for previous 5 days
  • Review menu accumulates total run times by zone from the last reset date
  • Rain delay of 1 - 7 days may be selected (to pause and automatically resume operation)
  • SLW Weather Station extended rain delay programmable from 0 - 99 hours
  • Run/Soak cycles allow setting of maximum run time and minimum soak time by program for use in Standard mode only
  • Zone-to-zone delay programmable for 1 min. - 3 hrs. to accommodate slow closing valves and recharging of water supply
  • Master valve timing sequence with zone-valve programmable by "On Delay" (1 sec. - 1 min.; 2 sec. default) and "Off Delay" (1 sec. - 3 min.; 5 sec. default) to allow for line fill and slow-closing valves
  • Master valve/pump start operation assignable On/Off by zone
  • Clear program function to selectively delete an individual program
  • Clear all function to delete all programs
  • Backtrack stored program feature allows contractor to easily store a default program and retrieve the saved program in the event a customer improperly reprograms the SL800
Product Tag:
Top of the Line
Product Type:
Controller (AC)
Enclosure Type:
Max Station Run Time (HRS):
Light Commercial, Residential
Enclosure Type:
SmartLine 1600
Freeze Sensor Compatible:
Power Source:
AC Powered
Number of Programs:
Start Times Per Program:
Sensor Compatible:
Rain, Freeze
Rain Sensor Compatible:
Controller (AC)
Residential and Light Commercial
Enclosure Type:
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Browse 9 questions Browse 9 questions and 17 answers
Will this system shut down the station that it detects isn't running properly? I live on a hill and don't want to risk a landslide from the constant flow of water from a broken pipe or irrigation head.
So the whole system won't stop, just that station it detects as faulty.
angela on Apr 23, 2014
BEST ANSWER: I don't know about this particular device, but most systems will turn a zone on and off regardless of the conditions downstream from a vave, so a broken pipe or sprinkler head will stop flowing when the controller tells it to do so. But a defective valve can stay open; in my experience, this usually results in a continuous slow flow, so it's an annoyance and expense, but not dangerous.
SL 1620 keeps flashing off off off , nothing I do will stop this, how do I fix this?
Doug C on Jul 21, 2014
is the product easy to wire into an existing system?
A shopper on Jun 2, 2013
BEST ANSWER: Yes, very easy to wire, just make sure you label or mark the existing wires for the zones so as to not get them confused.
I replaced another brand of controller that was on an existing system with this one and don't regret it at all.
Does this product have a manual single station and manual all stations feature?
Fred B on Jun 1, 2014
BEST ANSWER: Yes. You can pick a station to run manually for X number of minutes (at least 1).

You can also select manual mode for all stations where you can pick how long in 10 second increments.

What you cannot do is, for instance, run stations 1, 4, and 7 manually. Though, you can set up a program to run those stations and then launch that program manually.

IMHO, these control panels are the best out there. I had to replace my 1624 with a 1620 last summer, and even given that (which was frustrating) I'd still recommend the Weathermatic control panels over any others.

The features and control you get over your system with them compared to others is WAY worth any added cost.
In the installation guide, it mentions SLM modules. The way I read the manual, it seems as if these are not needed for the SL1620 unit. I just wanted to verify that no other items are needed when I purchase this to replace an existing controller. Can someone verify that? Or post a pic of the internal layout of the 1620?
Mark M on Mar 24, 2014
BEST ANSWER: Yes sir you do not need any modules it is a fixed 20 station controller.
When you say "concurrentLY" does that mean one station right after another?
A shopper on Apr 28, 2018
whats the diffrence between the 4800 and the 1620 other than the amount of stations?
A shopper on Jul 11, 2014