View Full Version : Identify Circuit Breaker for HVAC
07-10-2006, 06:05 PM
I just purchased an older home and was planning on installing a digital thermostat. I looked at the breaker box and nothing is labeled. Is there an easy way to identify which breaker controls the HVAC unit? Was not sure if I should just have the system running and trip the breakers until the unit goes off. I am assuming it would only be one breaker, is that true?
07-10-2006, 09:02 PM
Turn the main off and youll know itll be dead,get a meter and check voltage to the air handler if you can when the air handler is dead the t stat should be dead,thats just most units i have seen,may be some different,whos to say.Also you can check voltage to the t stat,usually they are 24 volts on c to r,when this is 0 you should be alright to.This is pretty simple but if you think you can mess something up just get a pro,new t stat and install shouldnt be to expensive and also have em to check the system out,bet theyll find something for ya to spend money on.
07-11-2006, 12:03 AM
An a/c condenser is usually 220 volt supply. look at the breaker panel and see if you can locate all the double pole breakers(have outside unit running) you'll be looking for two breakers that have been tied together, so to speak. You'll see some numbers on the swithes such as 30, 40, 20, 15. these are amp ratings for the circuits, now oyu know one of these will be your dryer(30-40) and another will be a circuit for your stove(40) unless you have a welder in the basement the last one would be for the air conditioner.
in most houses the upper 15 amp breakers single pole will be for the furnace,either on the left or right side. if you follow the metal BX cable supplying power to the furnace, up towards the ceiling space(in a basement) you may be lucky enough to find a light switch that powers the furnace, turn this off and you can go about your stat install as this will disable all 120 volt in which disables the 24 low voltage which is what you'll be working on. but always, know how to use a multi meter and be sure to use it!!!
07-11-2006, 06:48 AM
If your knowledge level is this low, you might re-think installing your own thermostat.
07-11-2006, 07:22 AM
First off, why would he kill the 220 line to his A/C to put in a thermostat? Secondly, is it really smart to tell an obviously uneducated homeowner to "get a meter" and start sticking it on live wires to trace?
The EASIEST way to do it is to put the old thermostat to "Fan-On". Verify the furnace blower is running. Then start flipping breakers one by one until the blower shuts off. This would be the furnace breaker.
I agree with idontgetit, if you can't figure something simple like this out, maybe you should just hire a pro to do it for you (and get the equipment cleaned/checked while you're at it).
07-11-2006, 07:50 AM
Was on a call yesterday were renter decieded to change the thermostat, and after I checked unit found door off of York furnace and low voltage on thermostat wired wrong.
Best leave the wiring up to a professional and spend a little now or alot later..
And the rules state no Mr. FIX-IT help.
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