During the winter I replaced the thermostat in our house that controls
heating and cooling systems. I have split system with 5 wires coming
to the thermostat. When I was replacing the thermostat I accidentally
did short circuit and heard the air fan for AC on the attic going off
(this was the last time the AC worked).
All breakers are turned on, I have power coming into the coil outside
the house (at least to the breaker) and to the attic fan. There is a
switch on the fan and I have power coming through the switch all the
way to the motor.
From the thermostat there are 3 wires coming into the fan. As I
understand electricity the wires have no voltage and work as a switch
(short circuit turns it ON) and my accidental short circuit should not
cause any damage to the system. However, I can not get the fan or the
coil to work after replacing the thermostat. I even try to switch back
to the old one but no luck either.
How can I test the system and find out what's wrong. Could my short
circuit cause any damage?
It sounds like you shorted out the control transformer. You may have to
replace it or look for a fuse that may have blowen on the transformer or on
a curcuit board.
You will need a meter to see if you are getting 24 volt to the subbase.
The way I learned the wiring of the thermostat is:
Red = Power = 24 volt hot
Green = Go = Blower
White = Snow = Heat
Yellow = Sun = A/C
Blue = Cool = A/C
Your 5th wire could be the Common connection on the subbase.
First thing to check is fuse for 24V AC control voltage.
It is located inside air handler on the logic board. Automotive
blade type fuse.
Rule No. 1, when you work on something like that turn off power first.
Don't mean to reply to Tony, but I don't see gmail posters. It sounds like
to me, that you have independent heating and cooling systems. The thermostat
would have an "RH" terminal, and an "RC" terminal. If this is what you have,
and you didn't remove the jumper, you will have shorted out one or both of
the control transformers, or blown a fuse protecting them
Ok, you guys were 100% right on that. It was the 24V control
So the attic fan is working but the coil outside the house is not. The
way the wires are set up they come from the thermostat (3 wires) to
the control transformer and than 2 wires go to the outside coil. Is
there another transformer on the coil that I could have possibly
shorted ? I don't want to start playing with the coil until I get your
opinion on it.
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