[whbrink]

Greetings,
We have a late 1970's Carrier central air conditioner, that we seldom have used since buying this property 2 1/2 years ago.
I recently noticed that our air conditioner would start up and abruptly shut off, with the inside unit in the garage making a "clunk" noise after I heard a buzzing sound coming from the unit. After having my local utility out, they advised that I may need to replace the "contactor" (HN51KC024 - 24 volt coil single pole).
To that end, I went out to the Condenser and removed the access panel, then using a Volt Meter, verified that I have 240 v at the input connectors on the Contactor, and 24V coming from the Thermostat control wires (brown and blue). The brown 24 volt supply wire is connected directly to the "23 terminal" on the right side of the Contactor, while the other control wire (blue) is connected to the "T1" connector on the Condenser Logic circuit board. Then, a Purple wire on the "T2" Logic board connector, connects to the "23 Terminal" on the Contactor.
A third wire "Black" connects from the "T3 terminal" on the Logic board to the "11 terminal" on the Contactor.
While I am standing outside, next to the compressor and the air conditioner turns on, the Logic board appears to make a buzzing noise out of a small shiny component that appears to be relay. I also am not measuring any voltage out of the "T2 terminal" on the logic board when the system is trying to engage the condenser fan. Should there be 24V there as well?
When I push the center (spring loaded) connector on the Contactor, the Condenser fan turns on.

Do you think the Contactor is defective and should be replaced or the Logic board? Or is the logic board making a buzzing noise because the Contactor is not operating?

Sorry for the lengthy explanation - thanks, Bill

[wmproop]

If you have 24V coming to contacter and its not kicking in,, it stands to reason,power coming in ,coil not closing the contacts,NEEDS REPLACING.as long as you are sure there is 24 V coming to the contacter