AC Compressor wont kick on

[Jaks69]

I went upstairs last night to a nice warm room. I checked the air and I see the compressor is not kicking on (8 years old) I have yet to check, but from what i understand if you ohm out the cap and it reads zero the cap is dead. When I turn on the air the contactor pulls in and the fan turns on in the furnace and on the compressor outside. What can i check on the compressor to determine if it is good?

 

Up until last night, this unit has worked flawless.   

[JJDH]

Take an amp draw on compressor common see if its running. Second, the line outside, the smaaler line is liquid, is it warm, is the bigger line the vapor, beer can cold inside where it enters the duct work?. Get the temp split.  Those will tell u if the compressor is running. Is ur filter clean? Are the coils inside and outside clean. Do you have 240 volts at disconnect. Is there 110 on each leg? this could get very complicated very fast. Is there continuity to ground. Do you have guages? What aire your air temps in going and outgoing? what is the condenser air entering temp? What is the return air wet bulb temp? Piston or txv? What is the model and serial?

[Jaks69]

I ohm'd out the cap and the compressor side was Zero, I borrowed a cap from another unit plugged it in and the compressor started. I found the problem (bad capacitor) now I have to figure out what size it is, there is no writing on it. It is a Dual Run, Fan and compressor.

[AmTec Services]

What make and model? I might be able to help.

.....................AmTec;)

[JJDH]

DONT run it with the wrong size cap

[applianceman18007260692]

Get a HS650 torque multiplier and add it onto your existing cap. 

You can piggyback it on your existing cap and not have to worry about installing the wrong capacitor. What you do is connect it to HERM and Common. It will assist the older cap.

[RegUS_PatOff]

Jaks69 wrote:

I ohm'd out the cap and the compressor side was Zero ...

 

applianceman18007260692 wrote: 

Get a HS650 torque multiplier and add it onto your existing cap. 

You can piggyback it on your existing cap and not have to worry about installing the wrong capacitor. What you do is connect it to HERM and Common. It will assist the older cap.

old Cap was shorted ...

[applianceman18007260692]

OK I thought he said he was getting 0 reading. Oopz.

I am just an analog old fart in a digital world.

[ACtechGUY]

applianceman, I hate to throw firewater at you , But your recent posts regarding capacitors have been way off.

Lets assume you have a Run capacitor that is either totally failed(open circuit) or just a very low microfarad rating(incorrect cap for motor).

If you were to install a start capacitor and relay(commonly called a start kit) you almost certainly could start that motor.BUT!!!!

Start capacitors are only in the circuit for moments to seconds( depending on how long it takes the motor to come up to full speed. ) If you have the incorrect size capacitor , " a hard start " kit WILL start a compressor, BUT seeing as the start capacitor drops out of the circuit after several seconds, You now have a motor that is running with little or no POWER FACTOR CORRECTION (provided by a correct run capactior). This results in a motor that draws way too much amperage, causing motor overheating(BURNOUT), and a boatload of other things that damage a motor and its surroundings.

To sum up , NO you cannot just throw on a hard start kit to compensate for a incorrect run capacitor. That would result in premature motor failure... (like within several days to weeks)

[applianceman18007260692]

Well a hard start is simply an option to boost an existing capacitor which IS the correct one for the system, provided it ain't shorted. If they were not worth the effort would they still be on the market? I have had one mounted on my 3 ton miller unit here at the house since 2002.

[AmTec Services]

With all due respect to the masters. The hard start kits only function is to give the compressor a kick in the butt on start up. It drops the start cap out of the circuit after tenths of a second. The compressor now runs with only the run cap in the circuit between run and start windings providing a phase shift in the voltage. This increases the running efficency of the PSC motor. With a bad or weak run capacitor, the motor will over heat, and eventually fail.

A little trick for you all. If you cant read the numbers on the cap, use a black perm. maker to cover the number area. Wipe off the maker with a clean paper towel. The faded numbers will hold some of the marker allowing you to read the numbers. Dosen work every time, but has helped in the past.

Hope this helps!

.....................AmTec:D

[JJDH]

There are 3 types of start kits. A start thermistor (PTC) (a ptc/ relay or super boost), good for a start once every 5 minuts and a HSK which is a large mfd cap with a potential 521 relay. The 521 is the best option. The booster is ok but can only provide assist when its cool,. The proper way to check a cap is a capacitence test (read the micfofarads). A capacitor has bimetal similar to a fuse underneath the terminals. Too much heat and or heat and cool repeatedly will cause it to disconnect the terminals and pop its top to protect things. The dual run capacitor balances out the motor force simulating a 3 phase circuit for the motor or compressor to run. Each compressor or motor needs the right value cap it was designed for so you dont over amp or overheat the motor or compressor. In high efficiency scroll compressors you dont always need a start kit. If the metering device is non bleed and the juice is r410a then a start kit is more necessary. A failed capacitor needs further diagnosis to ensure the compressor or motor arent what cause the failure. The dielectric fluid in a capacitor is to insulate it and keep it cool. Od pcb caps lasted forever because the fluid was better, however it was a pollutant. There are some basics. Just my 2 cents Thanks

[ACtechGUY]

Well said JJDH,

Maybe we should compile all this good capacitor info and maybe get someone to make it a sticky. After all , something like 60% of my service calls these days are related to failed capacitors. (by the way does anyone know a brand/label/line of capacitors that will last more than 2 years?? I only use 440v rated caps and that that does not seem to help)

----Regarding start kits on scroll compressors.... Early scroll compressors did NOT like start kits put on them unless they came from the factory with a start kit. If a "kickstart" was added they would often not start reliably or just cause the start capicitor to EXPLODE(literally) after several months. I do love a good explosion from time to time.

[applianceman18007260692]

You guys are awesome.

[AmTec Services]

Been hearing good things about Amrad caps. I've installed a few as a test. I have the same problem with caps failing. But it is a good source of income!!!:shock:

......................AmTec

[JJDH]

Job security.....lol. We use mars caps. when We tune up a/c units the wiring gets new connections and all components are checked, if anyhthing is wearing out we recommend new parts. I have only seen a couple of new caps fail this season.

[ACtechGUY]

I am beginning to suspect capacitor failure is related to the high heat we have been having lately. I have easily replaced over 40 capacitors this summer.

Many failures seem to coincide with a spike in Temperature outside. Seems the caps with wax inside vs oil filled are more likely to fail in high temps. But I have seen many oil filled failed as well.

I have been training a green tech, straight out of trade school. Up until 2 weeks ago he believed the only thing that ever went wrong with a/c's was a failed capacitor. Seriously , something like 2 out of 4 calls a day is a failed cap around here.

I do not do "PREVENTIVE" parts changing. I have seen WAY to many 30 year old contactors. I have found the quality of replacement contactors and capacitors to be often not as good as the original parts in the units. I know that a cap built 8 or more years ago has a better chance of not failing vs a brand new capicitor. I am not doing my customer any favors by replacing their "OLD" part with a shiny new part that will crap out in a year.

[AmTec Services]

Agree on all counts!!!

......................AmTec:yikes:

[JJDH]

Each company has their own practices. When we do a tune up we test each component. Anything that is out of spec... we offer replacement to prevent breakdown. When contactors are fried and have a voltage drop, they get replaced with a quality part. Todays caps arent like those old grey monster pcb that lasted 30 years, besides when someone has a 30 yr old unit, it is so inefficient and outdated replacement or upgrade should be considered.