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.




Kitep wrote:

"Meat Plow" wrote in message
...

Check for 24 volts going out to the outside unit's contactor when cooling
is call for by the thermostat.


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.