APS-4C SC-40C compEnvironmental Technology Inc.’s David Mays shares his insights on specific or unanticipated situations end users encounter with their ETI products. Here he illuminates the tricky mix of APS-4C and SC-40C status lights and system operations.

The Concern

One end-user opened his electric closet door which housed ETI’s APS-4C managing an ETI SC-40C. He saw some lights on, but the indicator LED for snow for the APS-4C was not lit. However, the SC-40C’s lit LED indicated snow. The technician verified voltage on the secondary side of contact reported that it was on and working. Given these observations, the end user thought the snow LED lamp was not functioning. He wondered what it would take to replace it.

The Question

More precisely, he felt that since the contactor is kicking in and the system is operating, could we not also conclude that when the “HEAT” LED is lit then obviously the “SNOW” LED would have been also, unless the system was switched on via over-ride or the timer kept it on?

The Answer

The APS-4C snow light only comes on when its sensors indicate snow. However, the snow light on the SC-40C comes on as it receives a signal from the APS telling the SC-40C to energize the heat cables.

Why does this happen?

The APS-4C sends the signal to the SC-40C whenever the APS-4C is heating.

Imagine if the APS-4C is in a Hold On* time heat cycle: the APS-4C’s snow indicator is unlit because the sensors are no longer indicating snow and it is concluding its Hold On time.

Meanwhile, the snow indicator on the SC-40C will be lit, indicating that it is still getting a heat command from the APS-4C.  Once the APS-4C time runs to zero it will stop heating and the snow light on the SC-40C will go out.  Five seconds after it goes out the heat light will go out as well and the contactor will open.

During this master (APS-4C)–slave (SC-40C) function, the Hold On timer knob on the APS-4C is in control.  The one on the SC-40C is ignored.

  • If the heat cycle is manually started on the APS-4C, the same thing occurs.
  • If the heat cycle on SC-40C is manually started, then the timer knob on the SC-40C is used.
  • If the heat cycle is manually started from an RU-4 remote control, then the timer knobs on both the APS-4C and the SC-40C are ignored and the timer on the RU-4 is in control.

A final note

Even if you manually start the heat cycle on the SC-40C and then manually start the heat cycle on the APS-4C, should you then decide to manually stop the heat cycle on the APS-4C, it will turn off the SC-40C as well.

As always, please contact ETI with your questions or comments!

* Hold On time: the continued heater operation after sensors indicate cessation of the weather event that initiated the (usually) customer-determined heating interval