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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22682
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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My stat is dead (reads any temp it feels like!) I want to

Customer Question

My stat is dead (reads any temp it feels like!) I want to replace it with a newer smart stat. If I follow the rewire advice I just need to know I won't blow out my circuit board.
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: Several weeks and it's been 110 plus degrees
JA: Do you plan on doing the work yourself?
Customer: yes. Ian a general contractor and am confident I can do the required work.
JA: Anything else we should know to help you best?
Customer: No, I just have concerns about damaging my furnace if I don't use the darn evolution stat.!
JA: Did you check the furnace's filters?
Customer: N/A
Submitted: 1 month ago.
Category: HVAC
Expert:  BillyHvac replied 1 month ago.


My name is Billy.

The letters in the thermostat should be relatively the same. Can you tell me what terminals are currently used in the old thermostat? And have you obtained new thermostat yet?


Customer: replied 1 month ago.
bought an new stat but returned it when I saw my wiring was A B C D not the usual RGYW
Expert:  BillyHvac replied 1 month ago.


In the furnace they are other terminals available. The wires would need to be changed inside the furnace...and possibly the ac depending on how it is wired into furnace. Can you access the furnace?

Customer: replied 1 month ago.
there are no other wires but the condenser wiring seems to be parallel to the stat wiring.? the stat wire is only using 4 wires.
Customer: replied 1 month ago.
I can access furnace but not to easily
Expert:  BillyHvac replied 1 month ago.

Ok, The stat wire is using only 4 wires but how many are in the cable?

In the furnace we usually have a choice of wiring r,g,y,w,c......or abcd with a communicating thermostat

Some systems are dedicated and we dont have a choice.

However you can get a communicating Carrier thermostat that uses a,b,c,d and is wifi.

Just Google Carrier (or Bryant) wifi communicating thermostats. These will be a direct changeout with the a,b,c,d terminals.


Customer: replied 1 month ago.
I'll try but I'm still leary of harming my furnace circuit board. Should I be concerned?
Expert:  BillyHvac replied 1 month ago.

Your board has a 3 amp fuse to protect low voltage shorts.

AND you turn power off when swapping thermostats. The only damage on an infinity unit would be blowing the 3 amp fuse next to the led light on the circuit board..

Customer: replied 1 month ago.
Thanks I'll try it.
Expert:  BillyHvac replied 1 month ago.

Plus if you have issues just return here...once you rate service (5 star system) you have 30 days of follow up.