AC outside unit is not working

Problems related to residential installations.

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AC outside unit is not working

Post by sormon » Fri Jun 10, 2011 8:45 am

Hi there,
Few days ago I just tried to start my air conditioning and unfortunately i found out that the outside unit (fan and compressor) are not working.
I tried to see if is something wrong with the electrical part but i did not found anything wrong.
Yesterday i took the metal cover out (from the outside unit) and i checked more carefully to see if is something wrong in there and i found out that if i keep pressed with a screwdriver on the contactor the fan and the compressor will start running, as soon i will remove the screwdriver the fan and the compressor will stop.
Can somebody tell me, is the contactor fault or is the capacitor?
Please help if you know, i don't really want to spend $150 to $200 on a technician if i can do the job myself.

paw paw
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- AC outside unit is not working

Post by paw paw » Fri Jun 10, 2011 9:42 am

check the voltage at the terminals on each side of the contacts(not high voltage wires). If you have 24v on the call for cooling,disconnect power and replace contacts, If not check for damaged control voltage wire coming from the house to the out door unit and the wiring connections on the indoor unit , if the wiring is good, check the voltage at the transformer on the indoor unit, this supplies the system with control voltage (low voltage, 24v) to insure you have 24v going to the system, If you have 24v going to the system, it's possible there is a t-stat or low voltage wiring problem. If not check to see if the transformer has a fuse or a reset button, If no fuse or reset, replace transformer.

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- AC outside unit is not working

Post by cascadehvac » Fri Jun 10, 2011 10:52 am

dude there is 240 volts in there!!!!!!!!!!!! stop!!!!!!!!!!!
the contactor should close on 24volts from stat. that is what the other tech is saying. might be contactor, might be thermostat. prolly should just have a tech come out and diagnose. dont electrocute yourself

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- AC outside unit is not working

Post by nomadpeo » Sat Jun 11, 2011 2:54 pm

agree with cascade dude. if you had a voltmeter and knew how to use it, you would have already confirmed whether there is a low voltage signal to the contactor coil. my sense is that you should keep your hands out of it and spend the money on a tech.

there are a couple of observations you can make. is the indoor fan running on a call for cooling ? if it is, that rules out indoor unit power, transformer and probably thermostat. is your unit upflow in a closet or horizontal in the attic. in either case, there could be a float switch detecting drain water backup and killing the signal to turn on the outside unit. horizontal - look at the pan under the unit. is it full of water ? upflow - do you have a device inserted in a tee near the outlet of the drain with wires coming out of it ? in either case, you may be able to find the drain issue and resolove it yourself.

the less likely culprits are thermostat and broken low voltage wires. if you can gain access to the terminal connections on the thermostat, you can jumper 'r' to 'y' (only momentarily) while someone observes the unit outside. if it does not make the unit come on, the thermostat is ruled out. if you have a dog or a landscaper/maintenance person, look at the brown signal wire cable strapped to your freon line for possible weedeater or dog teeth damage.

good luck and stay alive.

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- AC outside unit is not working

Post by specialtyclimate » Sun Jul 10, 2011 8:35 pm

could also be a loss of charge switch or a high pressure switch preventing the unit from starting. doesnt sound like this unit gets annual service.

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