HVAC Controls 1

The common wire is used when you're wiring in a digital t-stat. You'd have to use batteries otherwise.

I was pausing,and play to take notes in this nice video.
today since I am rocky saw that superv and me in trouble call, he replaced an old tstat with dial and mercury inside to a manual modern version, but he did not connect the blue wire to anything even the blue was @ oldtst
red= 24v
blue= common 24v why we need 24 common volts what it is the use of it.
green= fan blower motor fan
yellow= 1st stage cooling = compresor
white= 1 stage heat
O= reversing valve cooling
B= heat pump in heat

thats what happens when your in a mobile office.

lol

Thanks for watching my videos. I talk to myself, too.

Gotta love those RITETEMP pos t'stats

i wish i would've found you 5 years ago when i was in a/c school. i like checking your sites out, my Fiancee' hears me talking to myself and thinks im a nut!

Yup. We'd get lots of those during the first cold snap when I did residential. Sounds like you take care of most of your accounts yourself. Nice gig.

You've gotta love those calls. I don't get calls like that since I'm the one that has changed all of the t-stats in the schools that I take care of.

... So now Joe Homeowner wires it the way he saw in the generic instructions that are with his new t-stat and it works for the summer. But then they switch the t-stat mode switch to HEAT which connects 24VAC in the t-stat to the "B" terminal at the t-stat. But Uh-Oh. Now the Blue wire is connected there, which is now a direct short to transformer common and they blow the fuse and/or 24volt transformer. That mistake always gives you a bunch of residential calls at the beginning of winter! :-]