No Display Only Clicking After Install....yep another one

No display, only clicking after install.
Not seeing much succes in other “no display and clicking” threads.
Any help provided will be appreciated !
Vince

Trane-XL16i heatpump with supplemental coil. 2-yrs old.
Old Thermostat Honeywell TH4210. 2-yrs old.
7-wire includes C-wire.
Battery backup.
Replaced batteries because friggin Rayovacs were leaking.
Saw corrosion on 2 Ic’s, not near the batteries, likely for the LED. I brushed corrosion off and thats when the LED partially failed, but A/C worked.
3wks later later 100% failed when I switched from A/C to heat.

7-wire mapping from TH4210 manual:

E-Blk-Emergency coil relay
Aux-Wht-Aux heat (coil supplement) relay
Y-Yellow-Compressor
G-Grn-Fan
O-Org-Ht/Cool-Valve. Energized in cooling.
R-Red-Power, secondary side trfmr
C-Gray-Common, secondary side trfmr

Followed Wyze app pinout mapping.
No display just clicking.
Tested: Rc to 6-wired pins 27v +, Rc to Common 1.5v, .
Not sure if C is supposed to have any volts being a common wire.
I’ve not tested anything at the air-handler controls, because system worked with the old stat untill it crapped out.

Tried these tests based on stuff I read from web sources.
Sucess with no face plate:
Jumped Rc to G…fan ran. Jumped Rc to Y…compressor ran.
No success: after face plate installed.
Removed: Wht, Blk, Org, but clicking didn’t start immediately.
2- separate jump tests : Rh to Rc. Y1 to W1.

Calling our amazing expert @speadie because I am totally HVAC ignorant :sweat_smile:

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Resolved*
Issue was with C-wire to controller board in the airhandler.

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Glad you got it figured out. Was going to say, R(c) to C should be the highest voltage of everything, usually it’s directly across the secondary of the transformer, while all the other R(c) to W/Y/G pins have a load in between them that drops the voltage slightly.

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