Ok, my central air doesn't work, my central heat does. Took the panel off
the unit and found out:
Blue (Rc) - Yellow = 0 volts
Red (Rh) - White = 24 volts AC
The furnace is new, put in last year by a professional installer. The AC is
old, and may or may not have problems of its own (I've not had the house
long enough to need it)
My pal Google tells me there may be a fuse on the board, which I will check
tomorrow. But wouldn't a blown fuse keep anything from working? If the
fuse is good, I'm guessing the board is bad, but with it being new that
seems unlikely. Anything else I should check?
The outside unit is wired to the same screws the blue (Rc) and yellow
thermostat wires go to on the main unit. If I'm getting 0 volts there, I'm
pretty sure I'm getting 0 volts outside. Thanks for the suggestion though.
You will get zero volts a the thermostat , this is normal because the common
side of the control transformer dose not go to the thermostat and to get a
voltage reading you would need to check from common to red RH (or blue RC),
(transformer power), common to yellow (for cooling) common to white (for
heating) common to green (for fan relay)
Checking the two thermostat wires AT the outside unit should show a 24 volt
reading IF the thermostat is calling for cooling..
As a test for cooling, you can bypass the thermostat by jumpering RC to Yellow
which will bring on the outside unit and the indoor fan if set on auto
(Naturally, if set on "on" the indoor fan willl already be running)
Same for a thermostat bypass test for heating only jumpering from RH to white
will bring on the heat (but not the fan right away).
Most thermostats have a jumper wire from RH (red-heat) to RC (red cool) and the
jumper is to be removed IF there is a second transformer in the outdoor unit.
IF you are getting 24 volts at the thermostat it's because you are checking
across an open set of contacts and picking up the common side of the
transformer from the contactor (in series).
Also if you are getting 24 volts, the fuse is not blown.
Thanks, that's pretty much what the guy who came out to check it said. The
Rh & Rc should have been jumpered together at the thermostat with the blue
wire not hooked to anything. People say money can't buy happiness, but it
did for me :)
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.