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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 852
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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Breaker trips on my 2twr3042a1000A. It tripped once about a

Customer Question

hi breaker trips on my 2twr3042a1000A. It tripped once about a week ago and I reset it and it worked. Now it won't reset. i suspect the start capacitor on the compressor (or a bad compressor). Any ideas?
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: about a week.
JA: Do you plan on doing the work yourself?
Customer: yes. I've replaced the fan capacitor on it a couple of years ago so replacing a capacitor is within my skillset. (I'm a master plumber with some AC experience).
JA: Anything else we should know to help you best?
Customer: do you know the sequence that this heat pump starts up? it's a Trane with emergency heat strips. I'm assuming that the compressor comes online first, then the condensor fan. If the compressor can't start, then maybe the capacitor is bad.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: yes. i checked both. when the thermostat calls for cooling, it instantly trips the breaker on the condensor/heat pump. the interior evaporator fan works with no problem.
Submitted: 2 months ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 months ago.

Hi I'm Brian and I'm here to help!

You could be right and it could be a start or run capacitor but the breaker tripping instantly could point to another issue. Do you have a multi-meter, specifically an ohm meter, and knowledge of its use?

Thanks,

Brian

Customer: replied 2 months ago.
I do have an ohm meter (and an amp probe).
Customer: replied 2 months ago.
the compressor start capacitor doesn't "look" burnt or exploded like the fan start capacitor looks a couple of years ago. There looks like a little bit of smoke (possible) stain under the resistor that is on top of the capacitor, but I'm not sure.
Expert:  Brian HVAC Guy replied 2 months ago.

Ok great! I'll help diagnose this. First of all, to answer your question, on a Trane 2TWR (XR13), the condenser fan comes on as soon as the compressor comes on which is as soon as the contactor is energized.

On a Trane unit, the start capacitor is a round plastic encased capacitor and usually has a resistor across the top of it. It can be difficult to tell if they fail because they don't bulge like the metal ones do. Without having a replacement start capacitor to try, the only way to diagnose the difference between it being just a start cap and a short is to take some measurements with your ohm meter.

First, TURN OFF THE POWER to the outdoor unit!!! Next short all the capacitor terminals to ground (unit casing is fine) with the blade of a screwdriver. Now, locate the common, start and run wires to the compressor and disconnect them from their connection spots. The common wire should be a fat black wire, the run wire should be a fat red wire and the start wire is usually a skinnier purple wire attached to the run capacitor (sometimes a dual run capacitor on most Tranes). When you get those disconnected, measure the resistance of each wire to ground and each wire to each other wire and let me know what you read. When measuring from wire to ground, use the highest resistance scale, when measuring from wire to wire use the lowest resistance scale.

Customer: replied 2 months ago.
Okay. Will do. I'm not at home right now to try this, but I'll get to it later today. Should the wire to ground readings be infinite ( or high) resistance? And the wire to wire should have continuity?
Expert:  Brian HVAC Guy replied 2 months ago.

It depends on your meter and how high a resistance scale it has. A cold compressor could measure as low as 1 meg ohm to ground and still be relatively ok. If any wire measures anywhere in the Kohm range to ground, either your compressor is shorted or there is a burnt wire at the motor terminal box that has shorted to the compressor casing or there is a skinned wire shorting to the unit casing somewhere.

The wire to wire measurements should be about 4 or 5 ohms from start to common, 1 ohm or so from run to common and the sum of those two readings from start to run.

Customer: replied 2 months ago.
Thank you very much. This is a big help. I'll check this out before I purchase a new start capacitor.
Expert:  Brian HVAC Guy replied 2 months ago.

If the resistance checks are all ok then wire it back up and yes, order a new start capacitor and relay. You can use a hard start kit in place of the start relay and capacitor, it's a two wire start cap and relay in one and hooks up to the compressor run capacitor where the start and run wires connect. A Kickstart KS-1 or Supco Super Boost spp8 will work good. You remove the existing start cap and relay to install either of these.

Customer: replied 2 months ago.
sounds good. the unit is 10 years old and probably could be replaced with a more efficient one, but if I can keep it going a little longer I'll be in good shape. Thanks for all the advise. i like talking to pros!
Expert:  Brian HVAC Guy replied 2 months ago.

You're very welcome. I'll keep an eye out for your next post if you have further questions when you get to working on the unit.

Thanks,

Brian

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