Ruud AC unit - all caps replaced, motor still doesn't start

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Old 07-26-19, 05:47 PM
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Ruud AC unit - all caps replaced, motor still doesn't start

I have a Ruud Achiever series AC that's probably coming up on 16-18 years old. The AC condenser and compressor both finally stopped running so I decided to replace the caps and check everything else. This unit has a 50/5 mfd dual run cap and an 88-108 mfd that's tied to a relay. I replaced both with same value new caps that I checked before installed, to make sure the values were good. I also checked the resistance on the motor leads (while disconnected) and it buzzed out okay - the two lower values added right up to the larger value.

Once reconnected and the cutoff re-engaged I checked the 248 VAC at the contactor. All good. I then engaged the contactor manually. The compressor came on but the condenser did not. I rechecked the wiring. It all looks good - matches the pictures I took of everything before I pulled the bad caps. Not quite sure what to do next.
 
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Old 07-26-19, 05:54 PM
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Welcome to the forums.

The compressor came on but the condenser did not.
The condenser is the entire unit. In it is a compressor and a fan.
Did you mean the fan is not coming on ?

If it wasn't coming on previously.... it could be a bad motor.
Does the fan spin freely ?
Did you try pushing it with a stick after powering it up ?
 
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Old 07-26-19, 06:23 PM
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Yes, the fan motor. It was coming on just before everything stopped. It does not spin freely, but I'm not really sure it ever did. I couldn't try push starting it while I had the manual start on the contactor - too awkward and dangerous. The motor did measure out okay, though.
 
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Old 07-26-19, 06:52 PM
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If it doesn’t spin fully then there’s a problem there that needs to be addressed.
 
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Old 07-26-19, 06:59 PM
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I couldn't try push starting it while I had the manual start on the contactor - too awkward and dangerous. The motor did measure out okay, though.
That's not a manual start..... that is holding the contactor in when you shouldn't be. Set the thermostat to cool and let the contactor be engaged like it should be. If it doesn't spin freely..... the bearings are shot and you need a new motor. A very common problem with fan motors.
 
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Old 07-27-19, 04:19 AM
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Thanks Pete (and for the welcome). I'll give it a try this morning.
 
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Old 07-27-19, 05:59 AM
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A question. The 24 VAC on one side to the contactor coil goes through (according to the schematic) a set of high and low pressure controls. Must the high voltage to the compressor be present in order for these controls to close the circuit, so the 24 VAC can reach the coil? I ask because I wanted to do a step by step - first see if the 24 VAC hits the contactor while the main power disconnect is pulled. That would make it just a bit safer to probe around if I had to. I can do it with high voltage present, but I always err on the side of safety.
 
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Old 07-27-19, 06:14 AM
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Control voltage is sourced off the transformer in the air handler.
 
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Old 07-27-19, 06:16 AM
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Hi, first off itís not a good idea to close that contactor manually, 24 VAC should be present when the air handler is running and the Tstat is calling for cooling, power to the condenser could be off at the disconnect.
Sure sounds like a bad motor.
Geo
 
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Old 07-27-19, 02:23 PM
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Gave the motor blades a shove with high voltage applied. Nothing. Measured the resistances across the motor leads and they're all good. I'm confused.
 
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Old 07-27-19, 02:41 PM
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Yes..... the bearings.... or more precisely.... the top bearing is worn out. When the power is applied... the armature is drawn against the windings and keeps it from turning.

Condenser motor failure is pretty common.
 
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Old 07-27-19, 03:42 PM
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I'll take your word for it, but wouldn't I hear even a hum from the motor in that case? I get nothing. No hum. Nothing.
 
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Old 07-27-19, 07:40 PM
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What is there left ?
You checked the windings.
You checked for the correct applied voltage.
 
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Old 07-28-19, 04:12 AM
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Yeah, I hear you. Well, at least it's still available for purchase.
 
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Old 07-29-19, 12:18 PM
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You're right, Pete. It turned out my next door neighbor was having service done and I asked the guy to take a look when he was done. He checked all my work (new dual and start caps, new contactor) declared all was good. Got the compressor going, no fan. Twirled the blades around some and said the motor was seized up. I ordered the exact Emerson replacement. Will be here on Thursday. I asked him how much a job like that would cost. He said "about $1000". I let him know I could do it myself. A few more days of heat isn't going to hurt me.
 
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Old 07-31-19, 02:01 PM
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Thank you again, Pete. My AC is back up and running, but not in the way I expected. I ordered a replacement motor. My old one was an Emerson K55HXKYE, a 1/8 HP, 1 Amp, 825 RPM job. I ordered the exact Emerson part number. What I got instead was a Genteq. It's 1/3 HP, 1.5 Amp, and 1075 RPM. Both are spec'd to use a 5 mfd cap. I gave it a try since I've been without AC for several days at this point. It started up fine, but I'm not sure if I should be worried about the higher current draw and higher RPM.
 
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Old 08-01-19, 10:27 AM
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I ordered the exact Emerson part number. What I got instead was a Genteq. It's 1/3 HP, 1.5 Amp, and 1075 RPM. Both are spec'd to use a 5 mfd cap. I gave it a try since I've been without AC for several days at this point. It started up fine, but I'm not sure if I should be worried about the higher current draw and

I don't think you'll have a problem. Probably the reason you didn't get an Emerson Motor is that Emerson sold their motors and controls business to Nidec in 2010. The supplier you ordered the motor from may not use Nidec as a supplier.
 
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Old 08-02-19, 07:19 AM
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Thanks @Casualjoe. I've since discovered that the original Rheem part number, 51-100999-01, had been replaced with 51-100998-08. The Genteq equivalent to this is 5KCP39HFBB89S. What I got sent is 5KCP39GGU965S. It sure enough works. I just don't like that I got the wrong motor.
 
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