Rheem Touch-screen clicking noises

[AlexGB]

I wonder if anyone can educate me on these new generation thermostats.

I have a Rheem 400-series touchscreen stat that was installed with my RGFD Contour furnace. I've always noticed that when it cycles on or off there's a noticeable, though not annoying, "click". My first question -- is this because new stats no longer use the little mercury-filled bulb, like the 20 year old Honeywell round that was here with the old furnace?

And what replaced the mercury switch, a mechanical switch that makes the clicking sound?

Third question -- and the one that's really puzzling me during this cold snap -- why do I hear TWO rapid clicks each time it cycles on or off when the outside temps are below 20F or so? As far as I can tell, the burner and blower are operating at about the same level as when it's warmer outside, and I see the same uppercase "H" on the furnace display.

The manual doesn't explain any of this, so thanks in advance for your insights.

[cdjones91]

cdjones91,

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[BaldLoonie]

Relays replaced mercury bulbs so clicking is typical of about all digital stats except a few that use triacs.

Not sure why the modstat clicks twice. If you have the H appearing, that means the furnace is receiving the modulate signal so the firing rate should be varying. Since the inducer runs on high on all but the 40% rate, it may be a bit hard to tell what level it is firing it just by looking & listening. Airflow would vary, that may be the only way to tell.