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View Full Version : Replacing an electric motor inside of an outside A/C unit. Do it yourself job?


bordelond
06-11-2007, 04:28 PM
I don't know how much more stuff I can have break on me ... now it's our home's A/C unit.

Long story short: the problem is reliably diagnosed and isolated to an overheating electric motor motor that turns the fan on the outside unit when the compressor is engaged. I would like to replace either the electric motor or the entire motor/fan assembly myself, as I cannot afford the ramped-up charges for A/C services in this area (here in SE Louisiana, they know we need it :mad: ).

Is this the kind of repair a do-it-yourselfer can accomplish reliably?

MrFloppy
06-11-2007, 05:01 PM
I recently replaced my indoor motor which had seized a bearing due to dirt/dust. It wasn't hard to do, my local HVAC retailer had the motor in stock. I think there are several popular motor 'sizes' and he had mine. It isn;t something you can get in Home Depot or Lowes. At least not here in Maryland.

If it is the fan motor on your condensing unit and not the compressor, it shouldn't be too hard. Remove the motor and take it to a HVAC supply house. Assuming that you don't have some rare exotic motor, you should be able to get a direct replacement.

Put it all back together in reverse order.

Remember to turn off the power to the indoor and outdoor units.

bordelond
06-11-2007, 05:39 PM
Thanks, Mr Floppy. I'll be needing an outside fan motor. Hoping the fix is as accessible as yours was ... but some preliminary research is revealing that the wiring may be a showstopper for me.

brossa
06-11-2007, 07:48 PM
I replaced the seized fan motor on our outdoor A/C unit last summer. After yanking the circuit breaker and confirming that the power was off, I pulled the old motor and took it to the heating/cooling shop that installed the A/C when the house was built. The guy there told me that it was something that I could probably do myself (since I had diagnosed the problem, pulled the motor, and copied the wiring diagram from the inside panel of the unit), and referred me to the local electric motor place, where they pulled a generic replacement for me. I had to cut the motor's driveshaft down to fit, and I couldn't thread the new motor's wiring back through the conduit that the old motor used, so I just cable-tied it in place. I also had to wire in an additional capacitor, which involved some modification to the junction box inside the unit. This was preceded by a lot of internet research, but I'm sure I saved a buttload of money, and now I know more about air conditioners. But be aware that the wiring may indeed get a bit hairy if the new motor is not a 1:1 replacement for the old one. The folks at the motor place were well-informed and were able to answer all of my questions about the wiring, to the point of helping me draw out a wiring diagram for the new motor - 'the yellow wire goes to ....., the blue to ...., etc.'

One final note: be careful around the capacitors!

danceswithcats
06-11-2007, 08:46 PM
Yes, you can do it, but there are some things which can skunk you. In addition to the above advice, take along the manufacturer/model/serial/tonnage of the condensing unit from which the fan motor comes. That will assist the counter folks in correctly matching the HP/rotation/everythingelse of your existing motor. Getting the fan blade off can be a challenge. I've had to use pullers and/or torch to get the old blade off, and you also want to carefully examine the blades for cracks near the root. A fan blade thrown will often damage/puncture the condenser coils and can also dmage the motor bearings.

Around here, the best sources would be WWGrainger or Johnstone Supply, but like many of the other outfits where I go, they won't sell to the public. Good luck.

Drum God
06-11-2007, 09:16 PM
One final note: be careful around the capacitors!


I just wanted to re-emphasize this one. The capacitors inside can KILL you. Even with the power turned off at the breakers, the capacitors store a lot of punch and can cause your continuing life functions not to continue. Don't touch stuff without testing to make sure it won't kill you first.

raindog
06-12-2007, 01:53 PM
I just wanted to re-emphasize this one. The capacitors inside can KILL you. Even with the power turned off at the breakers, the capacitors store a lot of punch and can cause your continuing life functions not to continue. Don't touch stuff without testing to make sure it won't kill you first.
And how would bordelond go about testing it?

I think there are many projects that are decent DIY projects. (and I've given advice on a few here) We don't know bordelond's experience level, but it seems that he isn't experienced in this area. I don't know what "ramped up" means but you're paying as much for the techs experience and knowledge as you are for his time.

To begin with, the capacitor may kill, but it's pretty unlikely. Instead, you'll get a mini bolt of lightning when it disharges into your body. :eek: Highly unpleasant, and something you won't soon forget, but pretty unlikely to kill.

To 'disable' the capacitor, short out across the terminals with a screwdriver, while holding the handle. (no part of your hand should be touching the shaft) THE POWER MUST BE OFF FROM THE DISCONNECT BEFORE DOING THIS, AND CHECKED WITH A VOM.

But there are many ways to mess this up if you have little experience. To begin I hope "reliably" diagnosed means an experienced tech did this and not your brother in law who works maintenance down at the plant. I alos hope it means you didn't screw the aforementioned tech out of a repair that you called him to diagnose and repair.

If you have the wrong RPM, HP, rotation, frame size etc you will have bigger problems. If you bend the blades when removing the fan, or beat the shaft trying to remove the blades (thereby "mushrooming" the shaft and making the removal impossible) you will have bigger problems. If the new motor has a different MFD rating than the old capacitor the motor may not run. If the old capacitor is part of a dual capacitor you will need to change the dual capaicitor, or know how to wire in the new one. (which will be different now if you isolate the capacitor)

I'm not saying "don't do it." There are a lot of people who have some background that lends itself in a practical way to home repairs like this. But if you have NO experience there remains the chance that your repair won't work, cause additional damageto the unit (like to the compressor that relies on the fan!), or damage to you.

bordelond
06-12-2007, 02:17 PM
To begin I hope "reliably" diagnosed means an experienced tech did this and not your brother in law who works maintenance down at the plant. I also hope it means you didn't screw the aforementioned tech out of a repair that you called him to diagnose and repair.
My father is an experienced appliance repairman, and has performed plenty of A/C repairs on my parents' home. He was never an HVAC tech by trade, but he was trained years ago on refrigeration, wiring, and several other applicable disciplines.

I already have an appointment with my in-laws' regular HVAC guy -- his cost to come out and visit was much more reasonable than the first few places I called. I'm dirt cheap, but I know when I'm beat ... gotta go with the pros on this one :(

engineer_comp_geek
06-12-2007, 02:40 PM
To 'disable' the capacitor, short out across the terminals with a screwdriver, while holding the handle.

The proper way to "disable" a capacitor is to short the terminals with a nice, big, fat, juicy power resistor. That way the energy in the capacitor is SLOWLY dissipated, instead of turning your screwdriver into a mini arc welder.

Be forewarned that capacitors can "recover" a bit even after they've been drained.

raindog
06-12-2007, 07:26 PM
The proper way to "disable" a capacitor is to short the terminals with a nice, big, fat, juicy power resistor. That way the energy in the capacitor is SLOWLY dissipated, instead of turning your screwdriver into a mini arc welder.

Be forewarned that capacitors can "recover" a bit even after they've been drained.
That may be true in the lab. I won't disagree.

But in this application however, I will tell you that the standard, common practice is to TURN THE POWER OFF and dissipate the charge with a screwdriver.** With this method the screwdriver is not turned into an arc welder, ever. (for the "ever" part, see below) Occasionally there is a spark, but most often nothing at all.

On the other hand...... Forget to turn the power off and the end of your screwdriver will be vaporized in less than a second, not to mention the sparks, noise etc. It will double your heart rate in the same time span. (Of course.....I've never done that myself......I've just heard about it..... :o )

(** I have removed, and installed hundreds of capacitors. I've seen hundreds others removed by HVAC technicians. I have never seen a power resistor used in the field in HVAC work. (certainly not in residential applications), and, I can tell you that the trade schools train techs using this method)

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