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dearjimmy65

Diagnosing my Mothers AC problem?

15 years ago

I'm a newbie here so Hello! I'm trying to diagnose a problem with my moms condenser. When my mom turned on her AC for the first time this season she knew enough to listen for the outside unit to turn on. When all she heard was a hum she turned it off. When I looked at it she turned the thermostat to AC and the hum was coming from the condenser motor area. If the compressor was locked up would the fan run? How about if the fan was locked up the compressor should still run? She turned it off. When off I tried to spin the fan blade and it seemed like corrosion was making it tight. As I undid the motor wires I got a slight jolt from a motor wire. Should there still have been power even when the thermostat was in the off position? Maybe that was left over power from the capacitor? It's a 25 year old Trane 2 ton unit with a GE 1/8 HP, 230V, 1550 RPM motor. There wasn't a seperate capacitor on the outside of the motor so I'm assuming it's either before where I unhooked the wire nuts or inside the motor.

Am I correct in thinking that I should have heard the compressor running even though the fan wasn't? The only breaker for the whole AC unit is a double pole. Since some power was getting there to make the motor hum I doubt the double pole breaker would let power to the moter and not the compressor. When my mom turned off the breaker the volts that the wire was reading (used a multimeter to test) went away. I did not try to turn the breaker back on to try it again. My question is are the compressor and motor on the same circuit? If the motor was getting power then the compressor should have too. Is it possible to turn off my own drier outlet(240v) and use pigtails running to the now loose motor to test the condenser motor (230v)? The fan blade is off, the motor spins freely now and I will secure it. Will using a 110v power wire for a few seconds to test the motor burn up the 230V motor. Maybe 110v won't budge a 230v motor. I'm wondering if I could use that to at least test it because that would be safer. Once I find if the motor works then I'll reinstall it and see if turning the breaker on brings things back to life. Thanks for all your help!!!

Comments (12)

  • 15 years ago

    The humming is the compressor running. The condensor fan is bad. Always disconnect all power as most is 220 in a condensor and they usually only break one leg with the relays, keeping the components hot to ground, even when not running. When very economically challenged, I have taken those motors apart and re-oiled them...usually didn't last long though...best to buy a new one and the capacitor for it...newer units will sometimes share a duplex capacitor with the compressor. Always replace it.

  • 15 years ago

    Re-reading your post...don't test the fan motor on 110, it will burn up. Once they start causing trouble, best to replace motor and cap.

  • 15 years ago

    First of all thanks for the input garymunson!

    In another forum someone tried to tell me that the 220v is split between the compressor and the motor with both actually being 110 volts. I don't think that's correct because the motor says 230v right on it! It also says: GE Motors model no: 21A135217P01 HP 1/8 HZ 60 Ph 1 CAP V 230 A 1.85 RPM 1550

    I'm thinking it wouldn't say 230v if it was 110v!!!

  • 15 years ago

    I think what he ment was that a 240vac circuit is made up of 2 - 110vacs lines. If you have a motor that runs on 240volts, then one wire to the motor is 110volts and the other wire to the motor is 110volts and together they make up 240.

  • 15 years ago

    Fluffybunnysui...There are two black wires and one green that was grounded on the motor mount. I assumed one of the black wires was a ground. I marked the ob=ne that shocked me and figured that was the positive. That was the only one I stupidly touched though. I can see how both could be 110v to add up to the 230v. I've not seen it done that way, but thanks for teaching me something!!! Now all I need to two 110v instead of messing with my 240v dryer outlet!

  • 15 years ago

    That's how house power is done, 3 wires from the power company. 2 wires at 110 volts each to the 'common' or 220 across each other. Attempting to get 220 from 2 110 outlets would hinge on picking 2 outlets that were wired on opposite legs of the 220. You seem an intellegent fellow capable of dealing with electricity but since you have already been shocked once, you may want to get a book or two on electrical repair and pay close attention to the parts on safety. 110 volts kills people because the frequency of the 60 cycle ac can disrupt your normal heart rhythm with just a momemtary shock. Many people are killed this way a year. If there is no one next to you with a defibrilator, you're done. You don't have to get 'stuck' holding a wire to die. BE CAREFUL!

  • 14 years ago

    Thanks for the caution garymunson! When I assumed the power was off I relaxed my caution and I touched the end of one of the wires! VERY DUMB!!!! A neighbor with 220v in his shop offered to help me today. I'll wrap the motor with a come along strap with a 2 x 4 included in the strap. That way the vise can grip on the 2 x 4 while also tightening the strap at the same time. I need to be careful because I was unable to remove the fan blade even after an afternoon of lubrication. Are they screwed on and then an allen screw to lock?
    Will I be able to use 220v on the two 110v wires on the motor?
    I thought of a diagnosis to the "hum." What I propose on doing is cap the wires that the condenser fan motor hook up to and flip the power on. If I hear the "hum" then I know it's the compressor and obviously not the fan motor since it's not even there!!! Sound good? Oh...I won't run it long without the fan installed!!! Thanks again for all your insight!

  • 14 years ago

    before changing that motor you can also check the capacitor to see if its weak or just bad. the motor could be fine. to check the cap if you have on your meter a mfd you can check to see if its bad. basically if it says 10mfd anything below i believe 5 or 10% it needs to be replaced. its much cheaper than buying a motor and less of a headache. when taking a motor off besides soaking it with wd40 you can also heat it up with a torch. just make sure you dont use a hammer and mushroom the shaft or you will really have fun.

  • 14 years ago

    myneon...in his first post he mentioned the fan being hard to turn at first, I've never had any long-term success freeing/lubricating them...that's why I got so adament about replacing both motor and cap.

  • 14 years ago

    I found a replacement fan at a local shop. It installed easy, but it looks like the compressor is not working too! I hope it just needs freon. Is there a way to jump the compressor like a car to see if it functions for a short time?

  • 14 years ago

    Jimmy...no on the 'jumping' compressor....you originally said you were hearing a hum when the fan was not turning. The fans are small enough that when stalled they are pretty quiet. I suspect the compressor was the source of the original hum and was running. Are you sure you haven't disturbed the compressor wiring? Many units have a duplex capacitor that starts both fan and compressor, both would have been wired to it. Check your wiring again. Everything has to be on it's particular terminal.

  • 14 years ago

    sounds like your compressor is locked up. it may hum for a short time and then stop and hum again in ten minutes or so when it cools enough to try to start again. You can check your capacitor and then verify you have 240 volts from the output of the contactor inside the control panel (trace the wires back from the compressor to the control panel two wires go to the contactor and one goes to the capacitor, you want to check between the two wires together). If that all checks out you need to get a clamp meter that goes around the wires and checks amps. check one wire at a time. there is a label on the compressor it will have an LRA number this is the Locked Rotor Amps. If your clamp meter reads that number or higher your compressor needs to be replaced

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