I have a Goodman Split Unit Heat Pump that has a chattering Contactor. It is only getting 18 volts to the Contactor, but when you disconnect it, the voltage rises to 28 volts. I have put several Contactors of different brands on it with the same results.
Any suggestions?

I have a Goodman Split Unit Heat Pump that has a chattering Contactor. It is only getting 18 volts to the Contactor, but when you disconnect it, the voltage rises to 28 volts. I have put several Contactors of different brands on it with the same results.
Any suggestions?

Could be a weak transformer, It might show voltage but not enough milliamps/VA. Use a minimum of 40 VA for the transformer. Now loose low voltage wiring can cause this and I have seen thermostats cause this problem also. Good luck.