Need AC diagnosis help, please

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Old 07-18-18, 05:49 PM
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Need AC diagnosis help, please

When the unit reaches temp set on thermostat, it shuts off. However, when the temp rises enough to re-start the system, it blows warm air, as if something hasn't quite engaged on the re-start. Need some help figuring out what's failing. Note: when I turn off the AC at the thermostat, and then turn it back on, the unit cools. It's only after it shuts off and then re-starts (maybe 5 to 10 minutes later, that the problem occurs. Thought maybe the capacitor was the problem, but wouldn't that prevent it from working at all? Thanks for any help.
 
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Old 07-18-18, 10:04 PM
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A capacitor is affected by heat. The fan and compressor require more starting energy when hot.

You need to go out and see what the condenser is doing on a warm/hot start. You need to see if the compressor is running and if the fan is moving plenty of air. If you can't determine if the compressor is running although you see the fan turning..... feel the larger/insulated copper line. It should be ice cold if the compressor is running,.
 
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Old 07-19-18, 12:40 PM
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Thanks, Pete. I followed your advice. Here's what I found: When the unit re-starts based on temperature, the fan kicks in fine, but it looks like the compressor doesn't. The unit sounds different, and the copper line is not cold/sweaty, like normal.
 
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Old 07-19-18, 05:54 PM
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Thr next step is to check the capacitor inside the condenser. First make a visual check to see if it's puffed out on the top. That would be a sure sign it's bad. If you're a handyman..... I'd recommend just changing the capacitor. They run around $20 and is good start in diagnosing the problem. Be sure the power is off to the condenser before working inside. You'd need to remove the wiring access cover. You can post a picture or two of what you see there.
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Old 07-20-18, 07:52 AM
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I'll give that a go, Pete. Did a little reading, and it looks like you have to be very careful with stored charge in the capacitor. Gonna look into that further, before swapping it out. I'll let you know how the old capacitor looks when I get in there. Thanks for the help so far!
 
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Old 07-20-18, 11:46 PM
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The caps rarely hold a charge for than a couple of minutes. After confirming power is shut off to the outside condenser.... you can use a screwdriver to short between the tabs to confirm a discharged state.
 
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Old 07-21-18, 10:32 AM
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I was able to get in there before the week of rain hits us, and was surprised by what I found. There's a hard-start resistor in there, and the capacitor doesn't look deformed at all. (of course, I couldn't get a clean shot of the capacitor label, without removing it). I guess the capacitor could still be at fault, even if it doesn't show physical signs, huh? I've attached the photos.
 
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Old 07-21-18, 10:45 AM
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Your pictures are good. I believe the hard start cap is not wired correctly. If you look at the top of the cap.... there are letters.... C, F and H or C, fan, herm. Am I correct ?
Blue = C - com
Yellow = H - herm
Brown = F - fan
 
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Old 07-21-18, 10:56 AM
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I tried, but couldn't see any of the markings for the terminals on the cap. I'm wondering also if the rustiness on the terminals could be a factor. As for the hard-start capacitor wiring, the unit has been wired this way since it was installed, as far as I know. I'll have to remove the capacitor from the bracket to inspect it better.

Another question: I've read that some people don't recommend shorting the terminals on the cap until you remove the wires, to prevent possible damage to other components. What's your take on that, especially since it's an older unit?
 
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Old 07-21-18, 11:25 AM
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Use a Q tip to wipe off top of cap. It looks like the hard start cap is on the blue and brown wire terminals which would mean it's on the fan as usually the yellow wire is the compressor line.

You will not hurt anything by shorting out the caps as long as main power is disconnected.
Older cap rarely hold any charge at all.
 
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Old 08-05-18, 10:43 AM
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Hi, Pete - finally got the thing open again and inspected the capacitor. It had leaked a bit against the back wall, so I'm sure it needs replacing. Of course, when I could finally see the label, it was half faded off! Murphy's law, right? I was able to read enough of the label to find a replacement. Are the Genteq ok, or are the AmRad or PowerWell better? I also took another shot of the wiring between the hot start and cap, since you mentioned that it looked incorrect.
 
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Last edited by flukeslapper; 08-05-18 at 11:16 AM.
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Old 08-06-18, 09:18 AM
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Thought of another question, after failing to find an answer online. Is there an easy way to test the old hard start cap to see if that should be replaced, too? Thanks!
 
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Old 08-06-18, 11:05 AM
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See if there's a wiring diagram on the back of the service door you could post for me. I still think there's a wiring issue there. I believe that hard start cap is wired incorrectly.

I would just change the main cap.
 
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Old 08-06-18, 11:33 AM
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I think you're right! Here's the wiring diagram. It does look like the hard start is wired wrong, based on some other info I've tracked down. If that's the case, what are the odds it's still functional? I'm about to order the Genteq cap to replace the original one.
 
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Old 08-06-18, 02:25 PM
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Great picture!

Yes.... it's wired wrong. It needs to connect to the yellow (C) terminal and the blue (H) terminal.
It will be ok. Just replace the dual cap and wire it correctly.
You're actually lucky it didn't damage the fan motor.
 
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Old 08-06-18, 08:03 PM
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Thanks again for pointing out that hard start wiring issue - I sure wouldn't have caught it myself! New cap's ordered, and we'll see how it goes. Hopefully, I can squeeze a little more life outta the old beast. I appreciate all your help!
 
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Old 08-08-18, 05:05 PM
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Quick follow-up. Completed the swap, and hooked up the hard-start correctly. Not only did it fix the problem, but I'm pretty sure the old condenser is actually running quieter now, too. It stopped making the strange pulsing noise. Thanks again for your help, Pete!
 
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Old 08-08-18, 06:54 PM
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Great news and good job. .......................................
 
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