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View Full Version : A/c contactor has 24 v on the red wire to grnd and 24 volts on the black wire to grnd


mwattigney1
Aug 4, 2010, 09:26 PM
This is causing the relay to not pull in due to both wires being positive. But the other 25% of the time, the black wire becomes common ground and the relay to work correctly without touching anything. Could this be caused by a faulty circuit board?

wmproop
Aug 4, 2010, 11:11 PM
What are wires tagged to on the other end, in the furnace/airhandler?
One should tie to common,the other to yellow post or yellow wire from the y post in the tstat

NorthernHeat
Aug 5, 2010, 03:06 PM
Something is wired in series with this circuit and is opening.
24V into contactor will read 24 V out of contactor until the output is allowed to go to ground. So a wire is loose or a pressure switch or other safety device is opening not allowing voltage back to neutral/ground.