Compressor not running

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Old 06-28-20, 03:33 PM
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Compressor not running

My compressor (Lennox XC14) stopped running today after running fine up until yesterday.

At first I thought it was the safety switch on the condensate pump since it looked like it was having trouble. Cleaned out the pump, verified it was working, but still no luck. Verified it wasnít a bad safety switch by bypassing it.

When I turn the thermostat to cool, by the time I get outside the unit is quiet and doesnít seem to be trying to start. Maybe the compressor shuts off if the fan doesnít start after some time? If I manually press the contactor switch, then I do hear a hum, but the fan doesnít attempt to start.

I assume this is likely the start capacitor? There are two separate capacitors (the run cap is definitely non-own) so Iím assuming the original was replaced at some point since the manual shows a single cap with three connections. Interestingly the run cap is the one that looks more likely bad (some rust on it).

The fan will move if I push it, but it doesnít spin freely.
 
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Old 06-28-20, 04:01 PM
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Here are some things to try.
1) Turn off the power to the condenser (outside unit). There should be an electrical disconnect nearby.
2) If you have a voltmeter, with the thermostat calling for cooling, check the voltage across the coil terminals on the contactor. They will be the smaller diameter wires and are often on the side of the contactor. You should see 24VAC.
3) If you don't have 24VAC at the contactor, check for voltage where the cable from the house comes into the outside unit.
4) If you have 24VAC at the contactor, the problem is in the outside unit.

Since you mentioned that the fan turns, but not easily, I suspect that the fan motor may be bad (bearings starting to seize). If the fan isn't running, the compressor will overheat and turn itself off to protect the windings.
 
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Old 06-28-20, 04:25 PM
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The fan will move if I push it, but it doesn’t spin freely.
Yes.... that does indeed sound like a motor with worn bearings.
 
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Old 06-28-20, 04:29 PM
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Thanks. Unfortunately, my multi-meter seem to have broken since the last time I used it. Looks like I'll have to replace that before being able to test. The thermostat and is definitely working because the air handler speeds up when the call for cooling happens. I've checked the wiring from the air handler to the outside unit and it looks fine. So, I can't verify, but seems unlikely to be the issue.

The fan moves, but stops immediately when I stop pushing it. We also have a heat-pump and that fan moves much easier and keeps spinning for a bit when I stop. So, yeah it sounds like it's probably a bad fan and I guess it finally reached the point where the capacitor can't get it started anymore.

The unit is a little over 10 years old, so I guess that's not unreasonable for the fan to need replacing. I had to replace the inside coil last summer since it started leaking, so I am hoping to get at least a few more years out of the compressor itself (or it would have been more economical to replace both at the same time).
 

Last edited by JAHMD; 06-28-20 at 04:46 PM.
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Old 06-29-20, 02:08 PM
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I was able to get a technician to come by and he confirmed the high pressure switch had gone off and the fan motor looked like it was starting to seize. I guess he reset the switch and the unit started up again including the fan. He recommended replacing the fan motor, but said it was OK to use while waiting for the part as long as I made sure the fan started up whenever it turn it on. He suggested cooling the house a few degrees cooler than normal and then leaving it off until it got too hot and then turning it back on manually so I could check.

He said the run capacitor was fine, but they replace it when they replace the fan motor as part of being able to warranty the new motor. He said they can replace the fan blade, but said he didn't think that contributed to the issue and it was more likely a power failure or surge.

Any reason to spend extra and replace the fan blade as well?
 
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Old 06-29-20, 02:34 PM
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Normally, unless there is damage to the fan blades (bent or broken), the fan is merely moved from the old motor to the new one. If the fan looks okay and doesn't appear to have any problems (unusual vibration), I wouldn't replace it.
 
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Old 06-29-20, 02:47 PM
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I don't normally replace blades unless they are damaged or badly bent.
 
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Old 06-29-20, 02:53 PM
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Thanks everyone!

This seems like it would be fun and manageable to try to replace on my own, but given they will warranty the work and I have quite a few other projects without any time already I'm going to pay a professional for this one.
 
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Old 07-04-20, 01:48 PM
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Still waiting for a part, but after the technician reset the high pressure switch, the fan did run again for a while before stopping.

I checked after that and it seemed slow to move. I turned on the thermostat, and the fan started to move freely again, but the unit didn't start since the high pressure switch was tripped. Since the fan moved freely again, does that still point to the fan or just the run cap?

Also - it's currently wired with a separate run and start capacitor. Is it better practice to replace with a combined start/run cap or it doesn't really matter?
 

Last edited by JAHMD; 07-04-20 at 03:11 PM.
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Old 07-04-20, 03:19 PM
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I actually prefer separate capacitors. Dual caps are a compromise.

Sometimes a worn motor will start when cool but as it heats up it slows down and once it's hot.... it won't start by itself again.
 
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Old 07-04-20, 04:10 PM
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Thanks. The original unit came with a single from the manual, so I wasn't sure.

It's been over 90 this whole week and things were getting pretty bad inside, so I reset the pressure switch and tried to run it. It started and has been running for about 30 minutes. I'm keeping an eye on it and will turn it off when I can't watch it.

I'm going to order a spare cap (since it's $5). I'm unclear if they are planning on replacing it with the motor which I understand is good practice given how cheap they are. The technician said they would, but the parts department didn't seem to know anything about it. Maybe they have them on hand so don't need to order them. Thanks for all your help and happy 4th!
 
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Old 07-04-20, 04:16 PM
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While you can order a new capacitor, there's no guarantee it will be the correct one. The reason I say that is because the replacement motor (unless it's an exact replacement) may use a capacitor with a different value. Also, often a new motor comes with the corresponding capacitor.
 
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Old 07-04-20, 05:06 PM
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Thanks Bob, that's a good point!

I would have been able to order an OEM replacement fan motor by now, so I'm hoping for what they quoted me it's an OEM part. I'm in the 1-day shipping zone from Supply House, so I can wait and still have the part next day if needed.



 
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