A/C compressor trips breaker when it's hot outside

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  #1  
Old 06-29-10, 01:16 PM
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A/C compressor trips breaker when it's hot outside

Have a split system, A/C condenser is on ground outside of house, starts right away and runs fine in morning and late evening when it's cooler, but when it's really hot outside, it runs for 10-15 minutes then trips breaker. Reset breaker, same thing. If I turn it on later that same evening after it's cooled down, it'll run all night no problem. The unit is about 20-25 years old, blows cold, and starts up immediately. This ONLY occurs when it's really hot outside. What could be the problem? (Will post make & model tonight or tomorrow!)
 

Last edited by ddavissn; 06-29-10 at 01:38 PM.
  #2  
Old 06-29-10, 01:52 PM
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A couple of thoughts here.

Look at the nameplate on the condenser unit. It should list the maximum circuit breaker rating (amps). Tell us that number and, also, the rating of the breaker protecting that circuit.

With a digital voltmeter, check the voltage at the contactor inside the condenser unit (should be around 230V). Do this (carefully) with the unit running when weather is hot vs. cool; report results here. If your voltage is dropping significantly during hot weather, that increases the current draw of induction motors. (If the voltage is dropping, we can suggest additional tests to help determine if it due to the electric utility or something in your house.)

Verify that no other loads are on the circuit supplying the condenser, including the indoor air handler (which must be on a separate circuit).
 
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Old 07-01-10, 01:56 PM
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Unit is a General Electric Model 21TA936H1F. Nameplate states the following:
COMPR MOTOR: 22.5 AMPS: 230 V: 1 PH: 60 CY: 98
O.D. FAN MOTOR: 2.9 AMPS: 230 V: 1 PH: 60 CY: 1/3
REFRIGERANT 22 ONLY CHARGE: 6 lbs 5 oz.
TEST PSI HIGH: 350 LOW: 150

There are two breakers bridged together for the condenser, each rated at 30 amps. I don't believe anything else is on these breakers since the furnace still continues to blow air (and there are no other electrical outages in the house) after the condenser breakers trip off.
 
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Old 07-01-10, 04:02 PM
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Please look again at the condenser nameplate and see if it says what the maximum breaker or fuse rating is (amps). It should be listed. Also, it should tell you the minimum ampacity of the circuit supplying the unit. Or, can you post a close-up photo of the nameplate?

Your total full-load amps (FLA) = 22.5 +2.9 = 25.4A. A 30-A breaker seems a bit borderline, but you can't substitute a higher rated breaker without more info: the A/C manufacturer's max breaker rating and the size of the wiring used on the circuit. Look at the cable from the main electrical panel to the condenser - the size should printed be on the cable's sheath.

Here, just as a point of comparison, is from my A/C's compressor nameplate:

FLA = 19.4 (comp) + 1.4 (fan) = 20.8A
Max breaker size = 30A

My breaker is rated 30A (same as yours), but your FLA are 22% higher. My conductor size is #8 (I think #10 would have been OK per code, but #8 gives lower voltage drop).
 
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Old 07-01-10, 05:07 PM
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Thumbs up Welcome to our forums!

One thing that is pretty easy to check is the temperature of the liquid line.

The liquid refrigerant line is the smaller of the two that enter your house.
If the outdoor temperature is not overly warm the liquid line should be in the range of 100 - 120 deg F.
If you were to feel this line with your hand you would not notice it being much warmer than anything outside.
Hot or noticeably warm could show that your outdoor condenser coil needs cleaning.

Shut off the breaker and spray the coil with a garden hose being careful not to bend the fins.
These coils can sometimes from the surface look clean but a deluge of black water coming from the coil will tell you it was dirty.

Your symptoms could also indicate a worn compressor but check for dirt first.
 
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Old 07-03-10, 03:11 AM
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A few other things to check, is the condenser coil clean? a dirty coil and make one trip in the hottest part of the day. The comp start pulling to many amps and bam tripped out. Another thing after a breaker trips a few times it gets weaker and the more it trips the weaker it gets. The run cap for the comp could be a few mfd's weak also. If you have a multimeter check the mfd value. tolerence on a cap is +/- 5% no more no less, hope this helps.
 
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Old 07-06-10, 04:04 PM
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I do have a pic of nameplate but can't seem to post here. My email is ddavissn@yahoo.com, I can email pic to you if you provide email addy to send it to. However, the information I posted earlier contains EVERYTHING stamped on the nameplate. I did a little Internet searching and discovered GE sold it's CHA division in 1982 to Trane. I found a website that purports to decipher GE serial numbers and, if correct, the unit was manufactured in December of either 1967 or 1977. The permit for the CHA install was pulled in 1968, so there's a very good chance this unit is the original and therefore 42 years old. Though old, it seems to run great.
 
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Old 07-06-10, 04:32 PM
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It's 42 years old, presumably operating with the same 30A circuit breakers? Correct?

I still think you should check the running voltage at the compressor unit when it's hot hot - and when it's cooler. If the voltage drops when it's hot, motor amps will increase. Please do that, if you're able to safely, and report back. If this is the problem, it's your power company's to resolve.

I can think of three other possibilities here.

1. Maybe the two 30-A breakers, presumably 42 years old, are now tripping at less than 30A. Replace them.

2. For some reason, perhaps something in the compressor has worn out, causing higher motor amps.

3. I think a weak run capacitor can cause increased motor amps. Replace the capacitor.

Items 1 and 3 are relatively cheap for a DIYer (maybe $30 total). If it's #3, it's probably time for a new compressor.

If you do decide to replace the ckt breakers, get a 2-pole 30-A breaker rather than two single-pole breakers like you have.
 
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Old 07-06-10, 05:58 PM
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Did you check the temperature of the liquid line in the heat of the day and/or wash your condenser?

It could be as simple as a spray of water to fix.
 
  #10  
Old 07-16-10, 12:11 PM
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Cleaning coil seemed to do the trick.

I removed the metal panels and thoroughly cleaned the coils. It's my guess this hasn't been done in the 42 years this unit has been there, since they were clogged with loads of dirt, leaves, weeds, dead grass, etc.

I've run the unit several times since the cleaning with no problems, so it appears this was the reason for the tripped breaker. I never knew that coils on an A/C unit had to be cleaned periodically, never heard of anyone ever doing it. As a Realtor, I will DEFINITELY share this knowledge with my clients.

Thanks to all who responded!

By the way, it's too bad General Electric got out of the business. This condenser unit dates from 1968 and works like a charm, starts up right away and blows real cold. Though I can't say for sure, it appears all of the internal parts are original. 42 years and still going...what a fantastic unit.
 
  #11  
Old 07-16-10, 07:54 PM
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typical wash the condenser from inside out,check the electrical from the compressor thru the contactor into the disconnect then into the house CB for tightness.the probable trip problem is with the sun blasting it at mid day your running a higher head and when it cycles off the pressures don't have enought time to equalize..so the result is the trip..the wash out might solve the tripping problem..might want to add a adjustable time delay relay on one 24V wire going to the condenser..check Grainger local store for #4E233 home owners are welcomed.$13.00...if an AC guy checks it out he will recommend a HARD START KIT be added it will lead to compressor burn out..hopefully the wash out will stop the trips
 
 

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