A/C will not come on unless contactor manually pushed in.


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Old 04-10-11, 09:29 AM
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A/C will not come on unless contactor manually pushed in.

Hello, my problem is just like the title says. My ac does not turn on, the thermostat will click and the blower fan will come on for maybe 15 seconds and then shut off. The 30 year old outside unit will not come on at all, compressor or fan. I checked the contactor today which also looks ancient and discovered if I push in on it the fan motor will start but will stop as soon as I let go. I am assuming the contactor will need replaced but I am not sure that will fix my problem entirely. The A/C worked last season just fine. Any help is greatly appreciated, thanks.
 
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Old 04-10-11, 10:35 AM
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The blower is the indoor fan, is this turning off in 15 seconds?
If it does your problem is probably inside. Do you have a float switch on the drainline?





If you are getting 24 volts to the outdoor unit when cooling demand is applied, check the time delay if you have one and check across the pressure switch(es).
 
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Old 04-10-11, 12:22 PM
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I do not see a float switch. It would be by the drain in the furnace closet correct? Yes the fan will come on for a short period of time when I first turn on the AC and won't usually try again unless I turn it off and then on again on the thermostat or if I flip the breaker. I don't have a working multimeter here currently so I cannot try to see if there is 24 volts at the outdoor unit. I assumed there was since the fan operated when I pushed in the contactor switch.
 
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Old 04-10-11, 12:54 PM
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Some float switches mount to the pan under the evaporator coil, others can install on a Tee in the drain, some install inside the evaporator coil housing.

Pushing in the contactor does not prove low voltage is present. It did prove that high voltage is present.

Does the air handler have a transformer or is 24 volts supplied by the 30 year old outdoor unit?

You probably need a Pro or at least a meter to diagnose this problem.
 
 

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