Replace older Honeywell chronotherm

[jasonpowell]

My antique chronotherms have separate wires going to clock terminals for the clock in the thermostat.  These are in addition to the wires for y, w, & r furnace terminals.  
my presumption is that these clock wires should be capped, taped and left in the wall.  Anyone have a different conclusion?

[jasonpowell]

Ok,  I've connected the white "clock" wire (I'll call it CW) to M5.  Then I took the following voltage meter readings at the site of the thermostat without any wires attached to the Nest backplate:  CW to R = .16; CW to W = 28; CW to Y = 15; R to W = 28; R to Y = 16; and W to Y =4.

[CoolingWizard]

Those reading tell that M5 is not a common.   Move the white and gray wires to the #1 screw of the 40 VA input at the bottom.  We are looking for 24 volts between CW and R.  The .16 show they are both the same side of the transformer.  If the #1 to White to R does not show 24Volts, move down to the #2 screw and try again. 

The AC Cooling Wizard

The AC Cooling Wizard

[jasonpowell]

You wrote:  "We are looking for 24 volts between CW and R. The .16 show they are both the same side of the transformer. If the #1 to White to R does not show 24Volts, move down to the #2 screw and try again. "

With CW attached to post #1 the readings were as follows:  CW to R = .003, CW to W = 28, CW to Y = 9.5, R to W = 29, R to Y = 8 and W to Y = 8.

With the CW attached to post #2 the readings were:  CW to R = 29, CW to W = .01, CW to Y = 7, R to W = 29, R to Y = 8, W to Y = 8. 

Presuming the later was getting the correct results I connected the wires to the Nest backplate and the Nes t began displaying.  However, I heard an unsettling sound at the furnace that sounded like it was trying to start, stop and retried.  Upon opening the front I saw and heard some sparking at the starter as indicated by the yellow line in the attached photo.  I shut the furnace off to be safe. 

 

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[jasonpowell]

Well, nothing has worked but I do want to thank you for your valiant effort to assist me.  All my best to you.