Contactor Replacement

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Old 07-17-18, 02:34 PM
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Contactor Replacement

So recently I decided to get two long unused air conditioning units (both central) up and running. I got one of them to work in a matter of hours just by checking every switch.... the other one will not turn on. The blower works and the switches are all turned on except for the contactor. When I manually forced the contactor on, the condenser unit finally turned on but as soon as I let go it immediately goes back off (even though the thermostat is on and blower is blowing air). I donít think itís clogged because it looks/feels ok. Does this mean I need to replace the contactor? If so what do I get? The contactor it uses currently is no longer made by Honeywell (RB424A 1032). Thank you
Martin
 
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Old 07-17-18, 03:08 PM
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While it's possible that the contactor is bad, you really should check to see if there is 24VAC across the coil terminals (usually on the side of the contactor). When the thermostat calls for cooling it sends 24VAC through a cable that runs from the house to the outside unit. This 24VAC may pass through one or more switches (low pressure, high pressure) and/or a time delay relay before it gets to the contactor. If there is no 24VAC across the contactor coil, then the problem is likely somewhere else. Also, some systems have a float switch in the condensate system. If the condensate drain plugs up so that the condensate doesn't drain properly, the water builds up, the float rises, and it activates a switch which turns off the 24VAC going to the outside unit. This is to prevent the condensate pan from overflowing and causing water damage.

Note that you can turn off the 240VAC to the outside unit (there should be an electrical disconnect box nearby) before checking for the 24VAC at the contactor. Since the 24VAC comes from the house, the outside unit doesn't need to be powered to check for the 24VAC. Turning off the power to the outside unit makes it safer to check for the 24VAC (no high voltage present).
 
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Old 07-17-18, 08:17 PM
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Thank you so much for your help. Unfortunately I donít have a voltage meter on me currently but I will get one ASAP. I tried running the AC by manually forcing the button down and running the fan. So far there have been no obvious problems and it is cooling well. No water seems to be leaving the system though which is somewhat odd. Will check the voltage as soon as possible
 
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Old 07-17-18, 09:56 PM
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Hopefully you get the issue fixed quick. No condensate could mean your drain is plugged and your pan is filling up with H20 which unless you can visualize the pan you might find out when a wet spot occurs on your ceiling (happened to me ). Also, you risk damage ($$$) to your compressor if one of your safety switches is the reason the power is being interrupted.
 
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