Carrier AC Compressor Tripping Breaker On Startup.

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  #1  
Old 07-10-19, 01:08 AM
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Question Carrier AC Compressor Tripping Breaker On Startup.

Hello, and thanks for your help in advance.

I have an older carrier AC compressor that just started tripping the breaker when the stat calls for cooling. Started when I tried to turn the AC off, the stat still showed the cooling system as on and would not shut off as normal (I'm not sue if the compressor was still running during this). After about 10-15 seconds I heard the breaker pop. Reset the stat and breaker and tried turning on the AC again. The breaker tripped again immediately but the blower fan on the furnace came on as normal, just no compressor, so no cold air.

I am not well versed in electrical systems but have a meter and am comfortable working on them with some guidance

So far I have checked fuses in the furnace and at the ac compressor. AC fuses are 2 large 15amp fuses. I can not see inside them but they look fine on the outside and where not warm or discolored.
Breaker in house is 30amp and looks ok.
Furnace looks fine and works normally for heat and blowing air.
One thing to note is the AC unit is taxed fairly hard right now as it is the hottest time of year and my older house has poor insulation for the time being.

I was thinking I would try replacing the breaker in the morning and if the problem persists look into replacing the capacitor on the AC unit.
Anything else I could check? Am I going in the right direction?

Any help would be greatly appreciated!

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Last edited by PJmax; 07-10-19 at 04:31 PM. Reason: resized picture
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  #2  
Old 07-10-19, 12:32 PM
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Replaced the breaker with a new 30amp and the compressor came on for about 20 seconds and then tripped the breaker again. Going to open the unit and look for loose wires or other damage that could be causing a short and look at the capacitor at the same time. What should I be looking for or are they any other steps I can take to diagnose exactly what the problem is?
I'm not opposed to calling a repair tech or replacing the unit, just would like to know if its something I can do myself first.

Thanks!
 
  #3  
Old 07-10-19, 12:40 PM
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The breaker now tips immediately on a call for cool again, the AC fan will just start to spin and then shuts off. I hear a pop from the unit, I assume the capacitor hitting the compressor motor to get it going. Will update with any additional info once I look inside the unit.
 
  #4  
Old 07-10-19, 03:12 PM
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Capacitor looks ok and tests ok on an ohm meter.
Checked for short in the compressor motor. I get an infinite reading when checking each terminal to ground and I get a reading of 0 when I check between any of the winding terminals on the motor. I believe that indicates a short in the motor windings and the compressor and or AC unit will need to be replaced. Does that sound correct?

thanks
 
  #5  
Old 07-10-19, 04:27 PM
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Follow up question. Is it possible to replace the motor without replacing the whole compressor or having to rely on a HVAC service? All local HVAC places are booked for several weeks and I have an uncomfortable 1 year old and want to see if I could possibly get this going sooner.

Hopefully someone will respond soon

Thanks
 
  #6  
Old 07-10-19, 04:28 PM
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An older 10 SEER unit from 1998.

No continuity from ground to the compressor wire leads is good. Means no internal shorts. In order to measure the resistance of the windings..... you need a meter with an Rx1 scale or auto setting where you can set it to manual and read very low resistances. You are measuring in the area of 10 ohms so a meter with a high R setting will only show a short.

Your problem sounds like a bad capacitor on the compressor. Change that first.

That looks like it has two caps. A dual section run cap and a single start cap. It may also be equipped with a hard start cap. A picture with the wiring cover removed would be helpful. Turn power off to the outside unit before working on it.

Carrier 38TKB (pdf)
 
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Old 07-10-19, 07:19 PM
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Hello, thanks for the reply!
So you got me thinking maybe I was not using the multi-meter correctly. (very possible, I am not very familiar with its use).
I have the requested picture of the wiring area attached.
Also I have a picture of my meter. When I took the measurements of 0 (actually 0.000 on the meter) I was using the 2m and 200k modes and the meter did jump around wildly before settling on 0.000.
When I took the measurement again using the 200 mode at the 3 O'clock position, I got the following:

Start/Run: 4.3
Common/Run: 1.6
Common/Start: 2.9

This looks a lot like the numbers that would indicate a good motor (as far as my basic research tells me ) as the two lower add up the larger number almost exactly.


With that information, do you think my compressor is ok?
Is there any other tests I can do on the compressor or capacitor to check?

I will have to wait until tomorrow to check with the local HVAC guys about getting a capacitor.

I've also included a picture of the compressor info and the compressor wire leads.

Thanks!

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Last edited by PJmax; 07-10-19 at 07:40 PM. Reason: resized pictures
  #8  
Old 07-10-19, 07:43 PM
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Yes.... the 200 ohm scale was the correct choice. The compressor windings look ok.
The 2M ohms position is 2 megohms which is very sensitive.... even skin will show resistance.

The cap looks ok visually. Is there only the one ?
If yes.... I'd change it.

Just a word of warning..... anytime you remove the plug from the compressor..... wear safety glasses. That seal can rupture if you pull hard enough on the plug/wires.
 
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Old 07-10-19, 08:19 PM
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Wonderful, I did it wrong, best news I've had today

As for the cap, I'm guessing you mean the capacitor?
Sorry, dumb question I'm sure, I just wanted to be clear as the first time I read the post I thought you meant to change the plug that houses the the wire leads on the compressor. I'm thinking you meant to change the capacitor and to warn me that I should have been wearing safety glasses when I disconnected the plug from the wire leads on the compressor?

Thanks so much for your help!
 
  #10  
Old 07-10-19, 08:26 PM
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Oh and yes, only one capacitor that I see, unless there is one in the housing around the fan motor on top. That is the only area with wires leading into it that I have not opened.
 
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Old 07-10-19, 09:19 PM
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That is the only cap. I see the fan wire on it as well as the compressor.
A second cap would only be for the compressor.
Some variations of that series shows a second cap.

Cap = capacitor.
If you notice in my posts...... I always say capacitor in the first post. After that I use cap.
 
  #12  
Old 07-11-19, 12:30 AM
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Thanks for the clarification. Sorry for the dense moment

Will update in the morning if I can get my hands on a new capacitor that quickly.

Thank you!
 
  #13  
Old 07-11-19, 08:22 AM
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AC Motor Start Boost Insurance

Problems with AC compressor starting are a common issue. While there are many causes for the problem, there is a device commonly called “hard start” that can be a big help in many installations. When used along side/parallel with existing motor capacitor as voltage drops during start it switches in as boost.

Hard starts have two wires that usually have spade terminals which are easily connected to existing motor start capacitor and ground.

Look on hard starts as backup insurance, costing less than $20. It make AC motor starting more reliable.

Electrolytic motor capacitors age, become less effective and have to be replaced every few years. A hard starts make a difference but also need replacing every few years so I keep a spare.

While there are many hard start brands and models, most residential AC can use one of these:

https://www.supplyhouse.com/Supco-SP...crease-90-277V

https://www.homedepot.com/p/SUPCO-12...-203566154-_-N
 
  #14  
Old 07-11-19, 09:14 AM
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Put a new capacitor in (different physical size then my old one but same rating) and the fan came on for about 5 seconds and the breaker tripped again. Now we are back to instantly tripping the breaker as soon as the stat calls for cool.

What should I check next?
Would a hard start kit potentially correct the issue by supplementing the capacitor?

Thanks!
 
  #15  
Old 07-11-19, 02:12 PM
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Would a hard start kit potentially correct the issue by supplementing the capacitor?
If there are marginal issues that preclude start even with correct capacitor then a hard start might make the difference. For $10 it is worth the try. Even on well running systems hard starts can occasionally make a difference. Look on it as insurance or booster.
 
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Old 07-11-19, 08:30 PM
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That line of units shows a hard start used in several sub models so it wouldn't be uncommon to be needed..... especially on an older unit.
 
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Old 07-12-19, 01:32 AM
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Had an appointment with a local HVAC service today. The tech initially said the compressor had a short to ground and was bad without really looking into it, I mentioned that I had checked for this and the result was negative. He did the ground test with a meter and found that it was indeed negative for a short to ground. He then measured the amps the compressor was trying to draw at start up which came out to 47 amps. I asked if a hard start kit would make any difference and he agreed to try it. I did not see the output rating on the unit but it was roughly 150% the physical size of my capacitor. He hooked it up to my capacitor and we tested the unit again with the same result, breaker trip at start.

He said my motor/compressor was definitely bad and would need to be replaced or the whole outside unit replaced.

Is there anything else I could try to save my existing unit?

I have 2 local companies giving me a bid on Monday for compressor replacement and for whole unit replacement. The second company will also check and confirm the diagnosis of the first company. Company 1 has ball parked the new unit at 4-6K and the compressor replacement at 2,250 installed. Compressor replacement could also be done much sooner (about 7 days vs. 4-6 wks for whole unit). Do not have any numbers from company 2 yet, they were recommended to me by a family member as being more reasonably priced.

Another family member suggested that I could purchase new unit on ebay for much cheaper and just pay a company to take my old unit out and put a new unit in (or alternatively hook the new unit up myself and then just have them charge it if needed). He had done this a few years ago and said his unit came per-charged and he and a friend (who was familiar with HVAC work) replaced his unit and furnace themselves. He was quoted 10K from a local company and did it for less than 3. This was attractive to me but I'm not sure how feasible it is for someone without a friend with HVAC training. I also wonder if I would need to change my coils in the inside unit to match the new outside unit or if it would come with the appropriate coils. I'm not afraid to do the work, as long as I have enough information to know I'm not going to cause myself more problems then savings.

Any of your thoughts would be appreciated, sorry for the long post, just a young home owner looking for info to help make a smart/informed decision.

Thank you!
 
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Old 07-12-19, 08:12 AM
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Am DYIer, a paper pusher, not mechanic. Replaced my 3 ton R22 outside unit 25 years ago. Still nursing the 50 year old AC attic unit. Have basic tools, vacuum pump from old refrigerator, and can silver solder.

The AC pro's make refrigeration far more complicated than necessary.. Became a DIYer because professionals were often incompetent, slow to respond and overpriced.

Before engaging professionals, durchii7 might get a $10 hard start at HomeDepot and confirm compressor/motors is bad. Some might call that “due diligence” before spending thousands of dollars.
 
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Old 07-12-19, 06:41 PM
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The OP has stated that the servicing company DID try a hard start cap with no improvement.

I would not recommend you purchasing your own unit as you won't get a warranty on it or from whomever installs it.
 
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Old 07-12-19, 08:07 PM
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PJmax: The OP has stated that the servicing company DID try a hard start cap with no improvement.
I do not trust service people, especially when they can make thousands of dollars on a deal. Still would do a $10 reality check.
PJmax: I would not recommend you purchasing your own unit as you won't get a warranty on it or from whomever installs it.
Warranties can be very difficult to collect on. In most cases depreciation reduces the amount if any, to insignificance. Every HVAC item I have owned has always lasted longer than the warranty. AND labor costs are not warrant-teed or can be a pissing contest.

It may be fantasy or wishful thinking, but the difference warranty periods a manufacturer offers may be a clue to quality.

Either way would save warranty but not make it part of buying decision.
 
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Old 07-15-19, 11:26 AM
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Sorry to be absent for a few days.
Couple of questions:

1. Are hard start kits basically a 1 size fits most or are there different strengths that can be tried?
2. I have more then 1 capacitor for the unit now, can they be connected in series to increase power or do the same job as a hard start kit?

Thank you!
 
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Old Yesterday, 02:26 PM
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Druchii72 ?1. Are hard start kits basically a 1 size fits most or are there different strengths that can be tried?
No, hard starts are not one side fits all. Many 120 or 240 VAC AC's can use a common generic one. BUT there are situations where finding the right motor capacitor and hard start can be challenging. And other things impeding motor start that may have to be corrected.

If a hard start makes a positive difference then there is hope. Look on hard starts as a diagnostic tool and possible quick fix, Not as the ultimate cure all solution. Starting air conditioner, alternating current motors under heavy load is a complex subject.

Druchii72 ? 2. I have more then 1 capacitor for the unit now, can they be connected in series to increase power or do the same job as a hard start kit?
Capacitors are usually not connected in series, maybe occasionally in parallel. Normally use the specified capacitor "mfd" value for the motor.

The significance of hard start is their auto switch which keep them out of circuit until voltage drops. When voltage is normal, 120 volts or higher hard start is not a factor. Think of them as a low voltage triggered booster, sub system, not as a hard wired capacitor.
 

Last edited by doughess; Yesterday at 02:50 PM.
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