A/C 24v getting 120v when condenser kicks in
I'm scratching my (sweaty) head with this one.
Last fall I disconnected my A/C unit to accommodate an extension on my house. At the time it was disconnected, everything worked fine.
I reconnected it in its new location. Ran 240V service and a new 18/2 control wire. I connected the control wire just as it was previously. When I turn on the unit from the thermostat everything starts fine but then when the condenser kicks in, the contactor sparks and the condenser stops working. I replace the contactor and nothing changed. I started troubleshooting with a volt meter and found that when the condenser kicks in I get a reading of 100+ volts on the 24V side. I can't find anything shorted out.
Any idea on what might be causing this?
Also, if I hold the contactor in manually the unit runs fine. I'm cooling my house now but there is no thermostat in the loop.