Honeywell Lyric T5 - a/c compressor starts then immediately stops


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Old 08-11-22, 04:16 PM
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Honeywell Lyric T5 - a/c compressor starts then immediately stops

I have a Honeywell Lyric T5 thermostat that is replacing a Braeburn 5000 5-2 (model BRAE500). I have a gas furnace in the attic and a Carrier compressor out back. Attic access is not possible right now so I can't grab the model but I do know it's a high-efficiency gas unit. The Carrier in back is your standard 15 year old suburban unit. The model number on the stickers has long bleached out. No heat pumps.

The system functioned normally with the Braeburn thermostat. It is powered by AA batteries. The wiring was as follows:
Wire > Thermostat terminal
R > Rh with jumper to Rc
G > G
W > W
Y > Y

The wiring on the Honeywell Lyric T5 is the same, with the addition of the blue common ground to C

Wire > Thermostat terminal
R > R (with ‘Rc’ switch in the up position)
G > G
W > W
Y > Y
B > C

The heat works fine, as does the recirc fan. However when the cooling system is engaged, the compressor begins to start up and then almost immediately shuts off. The compressor works fine with the original thermostat. The compressor also works fine if I jump Y to R.

Any suggestions would be appreciated, thank you!
 
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Old 08-11-22, 04:54 PM
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Welcome to the forums.

I'm a little lost. If attic access was restricted.... how did the blue wire get connected ?

​​​​​​​B > C
If you didn't go up to the furnace how do you know C is on B ?
And if B = C .... that means you have a Trane furnace..... is that correct ?

 
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Old 08-12-22, 07:20 AM
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Thanks for the welcome!

The light blue wire was the only other wire in the wall and the number of wires lined up with what I know about the system (non-heat pump) so I took the chance it was connected and it was.

In retrospect I should have grabbed my voltmeter before wantonly hooking it up but alas it properly powers the thermostat which it turn properly operates the furnace and fan.
 
 

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