Outdoor Unit Compressor Doesn't Start (but Fan Runs)

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  #1  
Old 07-16-13, 11:02 AM
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Outdoor Unit Compressor Doesn't Start (but Fan Runs)

Hello, I have a central air split system where everything's working except the outdoor unit's compressor will not start; the fan runs fine.

Is there a short list of things that could be wrong, like:

* Low refrigerant (and thus a leak);
* Compressor locked up;
* Hard start kit needed?

I'd like to know if there is anything else to add to the list and maybe how to test. I have a voltmeter and am a DIY-er.

The system in only 7 years old and I noticed that there's a capacitor with 4 wires on it (two to the fan and 2 to the compressor). I thought only 3 were needed for the fan+compressor(?). I also took photos of the outdoor unit's label, the schematic inside it and the air handler's label if needed.

I don't see any burn wires and the capacitor looks OK too.

Thank you!

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Last edited by tony17112acst; 07-16-13 at 12:37 PM.
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  #2  
Old 07-16-13, 12:30 PM
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Since you have a volt meter check the contactor first, turn on the system and see if there is 24v at the coil and 240 volt at the line terminal. Then come back so we know if the problem is with the compressor / starting components or it's on the control side.
 
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Old 07-16-13, 12:34 PM
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By "line terminal" do you mean 240 volts coming from the wires from the outdoor breaker BEFORE it connects to the outdoor unit?

Also, with the outdoor fan running fine, doesn't that prove it's already getting the 24 volt signal OK?
 
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Old 07-16-13, 12:56 PM
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By looking at the diagram, yes if the fan is running the 240 is present and the contactor is working.
You might have a bad compressor or a failed starting capacitor. You can check both with a multi-meter. Being your not blowing a fuse, check for open circuits on the compressor.
 
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Old 07-16-13, 02:16 PM
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Oh yes you are right. Both compressor and motor get their power together so the contactor is ok. So you don't have any low refrigerant / control issue that is preventing the compressor to turn on and like tomf63 suggests you may have a bad compressor or starting components (relays/capacitor).
 
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Old 07-16-13, 02:51 PM
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Thanks for everyone reply!! I'll be testing the capacitor tomorrow morning, but my digital multimeter only measures Ohms. I'm not sure how to do it.

Now, why is low refrigerant not a possible problem? I was betting that was almost certainly going to be the culprit. Does the compressor/condenser not get any power if there's low refrigerant?
 
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Old 07-16-13, 03:30 PM
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I had a hard time reading the wiring diagram (low resolution), however it appears that there is no "low pressure" switch on your system (not all systems have them). It doesn't mean that you might not be low on refrigerant, just that being low won't prevent the compressor from starting, since the system doesn't monitor the pressure.
 
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Old 07-16-13, 06:39 PM
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It is much cheaper to buy a replacement capacitor instead of a meter capable of measuring capacitance. Check the capacitor for bulging (sign of failure).
 
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Old 07-17-13, 09:37 AM
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OK, I did a rudimentary test to the capacitor with my ohm setting on the multimeter and it looks OK.

HUGE DEVELOPMENT: I went to test the compressor with my multimeter and found the RUN wire was burnt off! Now I'm in trouble! The terminal is a lug or post with a flat flange but the flat flange is burnt off (see photo).

Can anyone recommend a solution? I found products that attach to the connector (QuikLug, Term-Loc) but I don't know if the flange must still be present for these products to attach correctly. Both websites do not explain it. are these good solutions?

Thanks for everyone's input!

P.S. On the compressor's terminals:
I tested Common to Start at .02 Ohms
I tested Common to Run at .05 Ohms
I tested Run to Start at .07 Ohms, so everything looked good there.

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Old 07-17-13, 09:50 AM
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Either of the products you spoke of will work well.
 
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Old 07-17-13, 09:52 AM
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Will they work with half of the stud's flange missing?
 
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Old 07-17-13, 09:57 AM
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Yes,................. ..... ...
 
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Old 07-17-13, 09:59 AM
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OK, thank you.

Also, what would cause this major burning at the Run Connector? I have been reading other cases like this on the internet and it seems like it'll keep happening over and over. I have seen that the QuikLug melted too after installing. I'm scared :-( .
 
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Old 07-17-13, 10:38 AM
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Loose connection is the reason it happens
 
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Old 07-18-13, 09:03 AM
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OK, I used the product QwikLug to attach the wire to the burnt and disfigured stud ...and it started right up!

Thanks everyone for all of the input. I saved hundreds of $$ instead of calling a tech!

I just hope 6 months from now I don't have the same problem due to some underlying issue. But I'm happy to have central air now and will worry about that only if it happens.

-Tony

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  #16  
Old 07-18-13, 10:49 AM
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Great find and fix and thank you for updating us! Job well done!
I actually had to replace the connections at the contactor in my system this year because they were burnt. I'm thinking I might pull the cover off the compressor soon and have a look at those too just to be on the safe side.
 
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