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I had a tech come out and install a hard-start kit to keep a 4-year-old 3-1/2 ton Carrier compressor from tripping the circuit breaker. The compressor failed this summer. A second tech was suspicious that a compressor less than five years old would be tripping the breaker. He discovered a loose connection in the cut-out switch. Would the hard-start kit have been necessary had the loose connection been tightened prior to it's installation? I'm wondering if the failure could have been avoided with proper diagnosis by the first tech
In 2009 tech # one had come to respond to my problem of a 4-year-old compressor kicking the circuit breaker. Without even looking at the connections in the shut-off box adjacent to the unit, he went straight into control panel, checked compressor current draw at start-up and installed a hard-start kit. I thought it odd that a compressor less than five years old would be drawing too much current. Had no problems in 2010 but last month the circuit breaker started kicking off again late in the day.
Tech #one returned, checked coolant pressures and return temp, added some freon and started to pack up. I asked if he wasn't going to check the current draws. He reluctantly removed the control cover, checked draw and voltages and pronounced the unit was running perfectly before leaving with my $168 check. When the circuit breaker kicked off again the next day, I started to suspect the breaker might be worn out. Called an electrician a few days later.
He replaced the breaker switch, again without checking the connections at the shut-off box, and within eight hours my compressor had died - coils shorted to ground - confirmed by tech # one who quoted me a price to replace the unit. Now I called a contractor I knew asking if he knew any good AC techs. He referred me to tech # 2 who, in my first call, was immediately suspicious that my original problem may have been in the wiring, not the unit. His reasoning was that a compressor less than 5 years old shouldn't have been giving me problems to begin with. He came over to confirm my compressor was shorted out. He then did what no other tech had done since I owned the house - popped the cover off the shut-off box and tightened the leads at the terminals - black wire loose, white wire "very loose."
My question is whether that may have been my problem all along and would a hard-start kit have temporarily relieved the symptom -tripped circuit breaker- without curing the problem.
Reply:
Tx Red: you and your second HVACR Tech have come across a useful diagnostic step: check for loose, or even burnt or arced wiring connections. I can't be sure of the answer to your question, as time has passed and we can't know for sure what conditions the first tech saw. A bad relay can cause compressor start problems, and I pose that its possible that arced, burned, or loose connections at the relay could make it misbehave.
Your thesis that a loose wire could have been misdiagnosed as a hard-starting A/C or heat pump compressor motor is reasonable but not, IMHO, absolutely proven by events. A compressor start relay (or most other switches) that are loosely wired will typically experience arcing at the loose connection (an event that can, by the way, when the circuit is active or the switch closed, draw higher amps than normal due to the resistance at the point of arcing and corrosion.) Adding a start-capacitor is adding a device that gives a big voltage surge just during motor start-up. A voltage surge that normally is overcoming inertia in a still motor might also overcome a start relay contactor resistance, caused by damaged or burned connecting points, or by a loose connection that was in effect acting in that same fashion. The start capacitor is delivering voltage and pushing the motor into rotation.
So without being an E.E. but with some experience around this topic, my reply is "could be" but not that we can say for sure.
Also FYI even a brand new A/C compressor could become hard-starting due to other system problems that cause internal damage to the device or even by (perhaps less likely) a manufacturing defect, events at the property, even general power delivery conditions such as abnormally low voltage. To research the topic you'd look for events that can damage the start winding on an electric motor.
useful step. Often service techs, contractors, and some investigators become habituated to a short cut of trying the "fix" that usually works successfully and fast.
IF the original start relay or contacts that were found to have been loose is still installed, one could investigate further by inspecting that device for evidence of arc burning or damage.
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Comments
(July 27, 2012) DanJoeFriedman (mod) said: Cristie
Regarding "how long can the unit stay on trying to reach set temp" the answer is ... it depends. It depends on quite a few variables such as
- the outside temperature - the inside temperature
- the rate of heat gain of the building, sun exposure, weather, direction orientation of walls - the SET temperature of the thermostat
- the capacity, design, of the cooling system - the cleanliness of the air filter
- the presence or absence of duct defects such as crimps, or crushed ductwork or air leak
Since some of these variables are different from hour to hour and day to day - weather - and others vary by human action - thermostat settings - we can't expect there to be a standard number of minutes or hours that a cooling system will stay "on" trying to reach the set temperature. In fact if we make the set temperature low enough the cooling system will run forever without reaching it.
A more helpful question to ask is: does your system seem to be working differently than it used to - taking weather changes into consideration? and is there good air flow at supply registers and is that air cool?
(July 26, 2012) Cristie said:
I did slightly bend a few cooling fins but I fixed them back to normal but what else I need to know is b4 I cleaned dust off the evp , could dust have gotten sucked through cooling fins and clogged something? I know the outside drain
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hole isn't plugged up so maybe some other area? I know it ran great a yr ago new with 95+ degrees outside & now it doesn't get as cool as it should and my MAIN question was/is how long can the unit stay on trying to reach set temp I remember it cycled more frequent than before I cleaned evp... I don't want to blow my window unit ..any help, PLEASE
(July 25, 2012) Anonymous said:
Christie the equipment should be able to run as you describe. And while there may be more to your question than was evident, if dust was removed from the evaporator coil that's good, helpful, and not harmful - let's hope no one bent or crushed the cooling fins.
(July 25, 2012) Cristie said:
Will dust covering the evp coils but then sucked out cause a problem fo the window unit?
(July 25, 2012) Cristie said:
Is it ok for my window unit to run with cold air without taking a break even though the desired temp isn't reached. When I first bought unit it seemed to cycle off & on and now when on coldest setting it isn't cutting off is this going to break the unit does it have to cut off (the compressor) I guess or is it ok to keep running hours or until desired temp is achieved please tell me
(July 14, 2012) Roland said:
Thank you!!!! You saved me a lot of trouble and expense with your article on the capacitors and all the other excellent information
Thanks again
(July 8, 2012) Charles said:
Outdoor A/C unit. Temps in the high 90's. Found compressor running, but fan stopped. Found badly corroded connection between condenser fan and capacitor. Female connector was burned and barely in contact. Wire charred for about 1/2" at connector. Removed burned end of wire, scraped the copper, replaced connector. Unit ran normally until the next day.
Now starts normally, but 20 to 30 minutes later,the condenser fan shuts off. Feels hot from mounting point. Compressor still running. Shut system off for 30 minutes. Repeat, unit starts normally etc. When running, the inlet line is cold and dews normally.
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Cleaned all contacts on capacitor. No change. Fan runs until the case temperature is around 130 degrees, then shuts down. Fan case temperature then climbs to 146 degrees before beginning to cool.
Tried to check capacitor. In checking resistance, got no reading. Then put voltmeter across terminals and registered a declining voltage. Capacitor MAY be okay.
Checked voltage. Ran 240V from T1 to T2, 108 to 112V from capacitor to T2. Still not sure what the problem is, but starting to suspect the fan a bit more.
(July 1, 2012) Anonymous said:
if compressor and the fan motor donot come on what can be the problem
(June 30, 2012) DanJoeFriedman (mod) said: ColdShot,
If the system runs for 10 minutes and stops, it could be overheating - maybe a failing motor; it's common to try swapping in a start/run cap first though.
(June 30, 2012) xXxColdShotxXx said:
I have been having problems with my outdoor A/C unit. It will start, but after 5 to 10 minutes the motor just stops turning and it just hums and it starts blowing warm air through the ducts. What do you think may be wrong with it, is it a bad capacitor or relay or what? Thanks for any help.
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George Fazio, reader, contributed comments on failed starter capacitor diagnosis by noting the bulged capacitor ends. 09/25/2009
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Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course
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Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
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Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard Asbestos HVAC Ducts and Flues field identification photos and guide
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