If your evaporator coil has a TXV (thermostatic expansion valve,) your installing contractor should have installed a hard start capacitor. If he didnt, he needs to return and install one.
Your thinking is correct, the hard start cap provides enough "juice" to start the compressor motor
and get it up to running speed.

"...sensitive to current fluctuations..."

You are seeing a voltage droop from the high starting current the AC pulls.
There are no fast pulses produced, just a droop in voltage that then rises back up smoothly.
It can be hard on the compressor, but is not a threat to anything else.

Thanks for the responses.
Out of curiosity, what is it about having a TXV that necessitates a hard-start capacitor?

A TXV doesn't allow the system to equalize like a fixed oriface does. Consequently the compressor starts under a higher head pressure. The hard start kit in effect gives the motor more starting torque.

It's normal for the lights to blink when the outdoor unit starts, but only to some extent. Have it checked and if it bothers you, have a start kit installed anyway if it will fit.
When I want to check and see if the outdoor unit is being called for by the thermostat, I turn the stat to cool and see if the lights blink if even slightly- this tells me it's calling or that the outdoor unit is running. If the lights dim for more than 2 seconds, there is a problem. If there's no blinking, there's a problem.
Some scroll compressor don't need a start assist, but I still like to see it installed if there is a TX valve. :)

If you don't mind humoring my quest for knowledge a little further.. =]

From what I understand of how a TSX valve works, wouldn't it only prevent equalization if it was engaged? i.e., when the temperature of the suction line is high enough, the tsx is just like a piece of pipe, and it's only when the tsx actually engages and shunts fluid directly over to the suction line that it acts any differently. So, I guess two questions: Am I misunderstanding how the tsx works? And, when it isn't engaged, would it still cause a problem with equalization?

(Please note.. I'm not questioning the advice that was given, I'm honestly interested in the whys)

Thanks.

IMO, dimming of lights suggests a low voltage condition on that circuit. If the whole house lighting dims, then it is the main breakers. This is not a good condition for any electronics. It is hard on microwave ovens, tv's, blower motors, refrigerators and any thing that can overheat from low voltage.

What this is saying is either you have an overload on the entire system, or the individual circuit. You could have insufficient wiring, a poor connection, or a problem with the condenser.

This is not a healthy condition.. It puts a strain on everything associated with the condition. It shortens the life of all that is dimmed. Contrary to previous posts, it is potentially harmful to appliances.

I don't think it's unexpected at all to have the lights temporarily dim. Our home has 100 amp service, and the startup load on this compressor (it's a copeland scroll) is listed at 29.5 amps. I don't think it's reasonable to expect that you could start a draw of that much current and not see any effect. The dimming is very brief, and happens only when the compressor first starts. The wiring and connections are all brand new, as is the condenser.

I don't see any reason to consider this a serious safety hazard rather than an annoyance. I've been in homes where the lights dim ever so briefly when the garbage disposal is turned on, which is far less of a draw than a compressor. However, if it is safe and reasonable to use a hard-start capacitor on a scroll compressor with a TXV in place, then I wouldn't mind getting rid of the annoyance.

Thanks

IMO Bob is right. I would post the same question on an electricians forum and post back here with the responses.

Was a licensed electrician part of the install group?

With our new house, one of the 2 systems once did the same thing -- the dimming was extremely brief, and happened only when the compressor first started. A licensed electrician did do the service -- and we have a lot... 2 full panels worth.

I posted a question like this on the electrical forum almost 2 years ago when we first moved in. I was told that it is normal for such a large draw to do such -- even on a very large amp'ed panel install. I was also told that it could also be indicative of the service for the A/C being at the "bottom of the stack" in the breaker box, as opposed to being at the "top of the stack." And, FWIW, we do have a hard-start on that unit because Carrier requires it for linesets longer than 50ft and where the indoor coil is xx feet higher up than the outdoor unit.

I should also note that when the bulbs that were dimming were replaced with CFLs, the dimming no longer occurred. I can only assume that it's because the ballast within the CFL was acting as a buffer to the momentary large draw.

It is "electrically normal," happens all the time, and contrary to what Bob says, does not "suggest a low voltage condition on that circuit." And your microwave will only be affected if you are trying to dry the A/C coil inside it at the time.

Well DB,
You had a hack of an electrician do the job. I have done enough Electric to install large enough wire, so that it never sags. Even in dads 55 year old house, the 3 ton system does not dim the lights, I guess I installed the 12 guage wire correctly. When I changed out the panel, I ran a size larger to the weatherhead. I have seen many homes where the lights dim over the whole house, which suggests an under sized service. It may have a 125a meter box, but if the line from the pole is too small, it will dim the house. I have worked on MANY older homes in Dallas that have a serious problem. They were wired for 60a, then upgraded for 125. The service wire was never increased. They were not designed for HVAC, and the electrician did not do the job right.

As to my experience, I have supervised Electricians from coast to coast and in Canada, specifying circuit ampacity, and overseeing jobs. I have built plants, computer rooms, retail stores, hospital equipment. I even taught Master electricians tricks. I have worked with union, non-union in many locations. I have run enough wire to be called sparky. You just don't have a clue. When you make suggestions dealing with electricity to a HO, You should know what you are talking about. I do, you don't.

Anyone that tells you it is ok, should also be using a voltage recorder to make that determination. This is not imaginary. I guarantee you that a journeyman probably has never seen a voltage recorder. I used them many times in multiple cities to solve voltage problems. One spike from a loaded motor can kill the control PCB for any appliance or the HVAC. If you doubt my comments, research Florida and thier problems with power. Same thing.

There goes bob brown again! Now its the electricians in Texas who are useless and he's better that all of them,,"correction" he has supervised all of them! What trade is gonna be next? Gotta be plumbers,,,ya think? Any of you familiar with the story Walter Middy? The pathetic little soul who led a very interesting life IN HIS MIND! I think we have an honest to goodness real life one here folks. I don't know how many more times he can get those meds adjusted before they have to try something stronger. Maybe when he imagines himself a brain surgeon he'll give himself a lobotomy!

I tend to agree with Bob that systems should be designed to handle the starting current of any load without significant dip in voltage. I worked as an electrician for industrial construction companies for 12 years before getting into project management. I now manage and work on residential remodel jobs as well as industrial jobs. As I recall, the standard then for electric equipment (generators and loads) was that it must handle a 10 percent dip in voltage for 1 second, or a 1 percent dip forever, as specified and tested by various testing and standards organizations. I know that is still the standard for generating equipment in the US, but I'm not sure it still is for loads.

I would think you would notice a 10 percent dip for 1 second in a house, but my experience is that when you see the lights dim, the dip is usually significantly worse than that, on the order of 25 percent or more. You can upgrade the wiring, as Bob recommends, but you can also take action to ensure the present system handles the startup current by limiting the amount of that current through motor control features, such as the hard-start capacitor mentioned above.

I worked on a project that had one of the largest motors ever built, used to pump water up a hill about 2,000 feet for a major water conveyance project. It had to have its own motor-generator set to very slowly bring the motor up to speed. Without that the starting current would have been over a million amps, and no system can handle that.

We now live way out in the sticks at the end of a long distribution run, and everyone here was having their lights dim many times per day, or losing power altogether, starting exactly at 6:40 every morning. Turned out to be a newly installed cement pump at a nearby gravel mine. The local utility eventually installed additional transformer banks and other equipment to correct the situation, but did not reconductor any lines. I measured voltage transients of well over 30 percent during those times. We never had problems with our electronics, but that certainly does not mean everyone in that situation would have the same experience.

So, for the original poster, by all means install the hard-start capacitor and see if that does the job, but also check the entire system carefully to make sure you don't have any problems, whether from loose connections, incorrect installation, or problems with the compressor. I've occasionally seen motors draw way more than they were rated when starting or running, usually due to problems on the work side (pump, compressor, etc.). You'll need a good ammeter to check that.

Service is too small or overloaded.A hard start may ease the drop.Bob is still retarded also.

"As I recall, the standard then for electric equipment (generators and loads) was that it must handle a 10 percent dip in voltage for 1 second, or a 1 percent dip forever, as specified and tested by various testing and standards organizations."

More like 10 percent forever and more for shorter times.
The CMEMA curve link is below.
Any voltage between 90% and 110% is allowed to persist indefinitely.
It only take a very few percent to dim a light noticeably.
We are pretty sensitive to changes in light intensity.

Here is a link that might be useful: CBEMA curve

Bob, Bob, Bob... how could you have done all that for your Dad when it's 100F out for 100 days? What happened after the first week when the other Trane failed again -- who got priority to protect the microwave from dimming bulbs and servicemen?

And, since I lived the first 35 yrs of my life in Canada, I guess I'm just lucky that I missed you servicing our electrical in January, when we don't worry about it being to cold to measure how many digits you left on the breakers outside cause the HVAC dimmed your bulb at the wrong time.

" This is not imaginary. "

"I've occasionally seen motors draw way more than they were rated when starting or running, usually due to problems on the work side (pump, compressor, etc.). You'll need a good ammeter to check that."
Ahem, what are you talking about here? A motor will easily draw 4 or 5 times its running load current for a second or two on start up "all the time", and even a cheap amp probe will show you that. Its called locked rotor amperage and a motor will draw that much briefly when it starts. And all this crap about blaming it on loose connections and undersized conductors and things like that,, BULL! If things like that were the cause the problem would get worse as the motor ran longer not occur on start up!

Perhaps we are mixing "flicker" with "dimming".
If a split second flicker of the lights is bad, then 98% of the homes out there are wired incorrectly and all of the inspectors and electricians should be replaced. When I see the lights "dim" for as much as a second or longer (I don't mean Flicker) then I look for a problem.

mr.havac,

I believe you are confusing what Bob Brown refers to as a "GOOD" ammeter.

In his case he usually uses his tongue to detect the amperage & depending on the shock he can tell you to within +/- 50A what the current is.

By a "GOOD" ammeter he means the kind you actually pay $5 for at Radio Shack.

Bob, has it hit 100 degrees yet out there in Dallas?

In regard to the OP's question, I'd suggest installing the hard-start capacitor to see if it does make a difference. They are only about $15 & are easy to install if you are comfortable working around HVAC equipment.

If it does not make a difference report back & we can go through a debug process.

LOL, where you been hiding mike13? Don't recall seeing any posts from you for a while. Poor bob, seems like everybodies got his number. I only strike at him when he puts down his fellow tradesman. Pretty soon he's going to have his very own section in this forum. HVAC according to bob.

Maybe you guys can help me here. I do commercial refrigeration and everything (well almost everything has a T.X.) including bar coolers with a 1/8th H.P. compressor. Why is it that NONE of them have a hard start kit ? This is interally and externally equilized T.X's Explain that.
My answer is nobody knows how to adjust a T.X. properly or
takes the time. just my thoughts on this. what is yours ?
Actually i know the answer. I'm just being a prick. what is
your answer Bob, or anyone for that matter. No offense to
Bob. He does have some very good answers. Yes this is a test.

Bob Brown is correct in that the house lights are dimming because the main wiring to the house is inadequate for starting the 4 ton A/C system

I had a similar problem some years back and my next door neighbor who is a lineman for the power company told me it was because our old house had a 2 gauge drop from the power pole on the street to our meter. He suggested I call the power company to request an upgrade and when I did, they replaced the 2 gauge drop with a 2/0 drop and all my light dimming problems were history

Since Kodiac's house just has a 100 amp service, no doubt his drop is undersized as well and when hit with a 50 or 60 amp starting load by the compressor, the voltage dips . . . . probably to below 100 volts if he were to measure it. The biggest problem this presents is going to be that it will shorten the life of the compressor, since it's trying to start on just 90 or 95 volts and that makes it draw even more current, which isn't good for the windings

I would request a larger drop from the power company and see what they say

Don

Service is too small or overloaded.A hard start may ease the drop.Bob is still retarded also.I aint gonna say it again.

OK kalining, let me give it a shot. refrigeration vs. A/C. Different refrigerants. R12/ R134A approx head pressure 125#,, R22 approx. 220,, R410A 500# plus. Tougher to get those pistons moving. How am I doing so far? TXV adjustment,,, increase superheat/decrease spring pressure decrease superheat/ increase spring pressure. Adjustment 1/8 a turn and wait 20 minutes for system to adjust. Check superheat with P/T chart.
Or the Canadian way to adjust a cooler. I/8 turn in, grab a Molson out of cooler, guzzle down to check temperature, to hell with waiting 20 minutes! Tweak another 1/8 turn, grab another Molson, glug glug glug. Damn, tweak again. Tweak, glug, tweak, glug, tweak, glug. Just messing with ya big guy,,, how'd I do on the test?,,,,,,,,prick :-)

MR. HAVAC. you must have seen me adjust TX's when i wasn't
looking. The beer of choice is CLUB or what ever the customer has on hand. You got the Canadian adjustment right. Actually it is a trick question. All most all
commercial refrigeration units use a high - low pressure
switch piped into the suction line for the stat. If the
unit uses a wall stat it is electrically connected to an
electronically controled T.X. valve. This way the A.C.
compressor can NEVER start until the pressure is within
start limits. Some units also use delay on make timers in
combination. Most hard start kits will void compressor
warranty. If the compressor can't start under it's own
power it is replaced. this is the way we do it. If a customer has thousands of dollors in parishable produce in
a cooler that has a questionable compressor or it needs a
hard start kit it is automatically replaced, no questions
asked. Copeland had a bad run on some of their compressors
a few years back and supplied a hard start kit for temp.
repairs untill all bad compressors were replaced under
warrenty. This was the first time a hard start kit was
authorized. told you it was a trick question. Thanks for taking the test. Your results will be mailed to you in 10
working days :)

"Your results will be mailed to you in 10
working days :)"
Ten WORKING days?!!!!! Thats means I'll have to wait months for my results! ;-)

Can I have an ice-cold case of Molson Golden mailed to me in 10 calendar days or less? Will it still be ice-cold when it arrives?

I'll send it priority post. It will be there in 24 hours
for both of you major players. I'll have to sample a few Molson Goldens first to make sure it is up to the best quality.

"Club" beer??? Is that an honest to goodness brand of beer or is that some local horsep- - -? Cripes I hope you wash out the bathtub before you brew a batch of that stuff! LOL Club beer huh? Gonna have to look for it.

lol,is that like club soda or what?I will stick with my Miller Light or Coors Light.

Bama:

When I steam live blue crabs in Coors Light, they complain loudly. They believe that they should taste decent beer just before they meet their maker. Tough luck for them, I'm not wasting one of my "good" beers on the crabs.