Thread: Lights dim when A\C is running

In a fifty year old home with a 4 ton A/C central air the lights dim at startup and then continue to flicker for about 10 minutes. Dims for about 10 seconds and then returns to a normal. cycle gets longer you can stand by the condensing unit and hear the draw and watch the lights, this doesn't seem right can any one give me some direction. I haven't had it happen before, sometimes the lights dim at initial start up but I haven't seen it get going for like I said slightly over 10 minutes.

thanks in advance for any input

Blain

Similar Threads:

• Lights on GFCI for bathroom
• Pool Lights
• Tube lights
• Floresence Lights
• Security lights via a rain gutter

Check the Neutral at the service entry....probably a loose connection.


RR

If there is not already on on the unit, you can have your HVAC guy install a Hard-Start-Kit. That will typically reduce or completely eliminate the brown down at startup.

Phillip,

I had a "Hard Start" kit installed on my prior home due to the condensing unit tripping the breaker periodically.

Exactly what is a Hard Start Kit?

The compressor motor draws a lot of current when it tries to start. The purpose of a Hard-Start-Kit is to help the compressor get up to running speed very quickly.

A hefty charge of electricity is stored in a capacitor and is delivered to the compressor windings when the compressor tries to start. Once the compressor motor gets going, a control relay then takes the start capacitor offline. The capacitor then sits by and waits for the next startup cycle.

Originally Posted by Blain Plantz

In a fifty year old home with a 4 ton A/C central air the lights dim at startup and then continue to flicker for about 10 minutes. Dims for about 10 seconds and then returns to a normal. cycle gets longer you can stand by the condensing unit and hear the draw and watch the lights, this doesn't seem right can any one give me some direction. I haven't had it happen before, sometimes the lights dim at initial start up but I haven't seen it get going for like I said slightly over 10 minutes.

thanks in advance for any input

Blain

A few common things that might cause this:

Could be a loose neutral.

Did you check to see if the home has a 60amp service, on a 50 year old home this is not uncommon. If it has a 60 amp service, this is not really large enough for an HVAC system like you have.

thank you all, this board really helps me be far more effective than I ever could be alone. the electric service was upgraded to 125 amp service about 5 years ago.

I am sending the client a recommendation to have the "hard start kit" installed. For me the fact that it keep going over and over again was unusual. I stopped counting at 11 times (the lights dimming) and started looking at the clock the last huge draw was just over 10 minutes after the A\C was started it was this frequency that I had not seen before.

thanks again
Blain

Blain,

I'm not sure I would recommend the hard-start kit "specifically". I would recomemnd that you have a licensed HVAC professional evaluate the system to determine if that is the cause--first. If he determines one is not needed, then you will not have made an incorrect recommendation/ diagonistic error.

Chances are that an electrician would diagnose either the loose neutral (or whatever the cause is) or the need for a hard-start kit.

Just my opinion...

RR

I kind of thought that way, my paragraph to the client is at the end. I probably should have been a little more vague,but I think I should give my clients some guidance if I can. I know it is magnifying my exposure to more bad things than good but I think anybody can say something probably broken. People, buyers especially, really want to know what is the next step and why. I hate going to the doctor and spending money on tests when I am not really in the loop, you know what I mean.

Under the air conditioning heading "System draws a large volume of electricity , it affects the lighting in the home for a matter of minutes before settling in. I recommend having a qualified HVAC professional evaluate the system and possibly install a " hard start kit". If the system is not already equipped it will typically reduce or eleiminate the huge electrical draw at start up.

Under the air conditioning heading "System draws a large volume of electricity , it affects the lighting in the home for a matter of minutes before settling in. I recommend having a qualified HVAC professional evaluate the system and possibly install a " hard start kit". If the system is not already equipped it will typically reduce or eleiminate the huge electrical draw at start up.

I think you have the cart before the horse, so to speak. Identify the problem, but stay away from offering repair specifics. You could be miles off base with this diagnosis, which puts your "hard start" suggestion in a bad light.

Dom.

thank you I will keep that in mind for the future.

There are a whole bunch of factors which could manifest themselves in the manner you describe. For instance, you mentioned that it does this "over and over". One thing that could be causing this is that the unit is actually overcharged. Head pressure and amperage draw will swing back and forth if this is the case, and the unit will be extremely inefficient. Even an older unit, which initially has difficulty "getting up to speed', so to speak, will level out after a short period, and this is the only case in which a hard-start capacitor is warranted. I'm suspecting an older unit is in place, with a variety of factors in force, including the strong possibility of a loose neutral. I would simply refer it to the HVAC tech without being overly wordy. A 125 amp service should be ok.

Originally Posted by Jimmy Breazeale

There are a whole bunch of factors which could manifest themselves in the manner you describe. For instance, you mentioned that it does this "over and over". One thing that could be causing this is that the unit is actually overcharged. Head pressure and amperage draw will swing back and forth if this is the case, and the unit will be extremely inefficient. Even an older unit, which initially has difficulty "getting up to speed', so to speak, will level out after a short period, and this is the only case in which a hard-start capacitor is warranted. I'm suspecting an older unit is in place, with a variety of factors in force, including the strong possibility of a loose neutral. I would simply refer it to the HVAC tech without being overly wordy. A 125 amp service should be ok.

An overcharged system?

Forgive me (and not to bust your personal bubble Jimmy) but as somone who has been working on HVAC systems for 35 years and has solved this particular problem for hundred of clients, the overcharing of a system with refrigerant is not the cause of dimming lights in the dwelling at condenser unit statup.

Hell, the system does not even "know" its overcharged when the voltage is first thrown to the compressor and the lights begin to dim!

(Tell me if I am being too harsh here. I hate to sound like Simon on American Idle but some us appear to need that kind of reality check.)

Hmmm...well, harsh might not be the correct term. Instructive? Question, then...when head pressure varies because of an overcharge condition, amperage draw doesn't vary as well? Please explain for my edification or "butt kickin'".

Since I didn't receive a reply to that last post, I am going to assume that the person who basically said I was full of it realized his mistake and was embarrassed to come back.

Fact: Fluctuating head pressure as a result of an overcharge causes a corresponding fluctuation in amperage draw.

Given this fact, and assuming that there is a loose neutral involved, those two conditions together WILL cause dimming of lights, lock rotor amps notwithstanding. I stand by my original response to the original post.

Sorry Jimmy,

I was not intentionally trying to duck the question! I somehow missed your follow-up question when you posted it.

Yes, you are correct in that high head pressure does affect the amp draw of the compressor. The peak amp draw during that kind of fluctuation however is negligible when compared to the peak amp draw of the compressor at startup (without a start kit installed).

That was my original point and I concede that I stated it very poorly. If I offended you in the process then you have my sincere apology.

fluctuating head pressure could also be a result of non condensibles in the system, do you have gages on the unit or are you assuming the head pressure base on amp draw?

No apology necessary. This medium is probably the easiest one in which to be misunderstood. The original post mentioned something to the effect that he could hear it straining in mid cycle, and noticed that the lights dimmed a little as that happened. I probably should have specified that I wasn't talking about lock rotor amps. So, we're cool! I've seen this happen, and yes, another cause could very well be contaminants in the system...or even an outside chance of a bad expansion valve, if present.

Jimmy,

By your comments, you obviously know a thing or two about HVAC systems (as does Bruce III with his mere mention of "non-condensable" within the refrigerant system).

Would we all agree though that putting gauges on the system and evaluating the pressures of the system during operation goes well beyond the scope of inspection for the generalist home inspector?

Would we agree then that putting an amp probe on the line and measuring the operational compressor amperage draw during the run cycle goes beyond the scope of inspection for a home inspector who is a generalist and not a specialist)?

We would indeed agree on that point. My guages are safely stored away behind a mountain of my wife's stored stuff in the attic of my detached garage so I won't be tempted to get them out and carry them around. It's tough to do sometimes, but it's actually best not to even speculate on a report, and probably better to act (somewhat) dumb in the presence of a client. Bite yer tung, refer it, and move on.

"I don' know," (scratching your head, speaking to a client), "but it looks like it's got something to do with this here air conditioner."

There are a lot of reason to lights dim, when A/C is running. The reason that you see the lights dim, they are probably on the same circuit as the outlet with the AC. You can check that basically be found which circuit breaker in the panel turns off both the AC & the lights. The circuit breaker ought to protect you from overloading the circuit ( much voltage loss for long). If the circuit breaker starts tripping, make sure you turn off other items on the circuit before using the AC.


Thanking you..
Epackpolymers.com

Originally Posted by jakson

There are a lot of reason to lights dim, when A/C is running. The reason that you see the lights dim, they are probably on the same circuit as the outlet with the AC. You can check that basically be found which circuit breaker in the panel turns off both the AC & the lights. The circuit breaker ought to protect you from overloading the circuit ( much voltage loss for long). If the circuit breaker starts tripping, make sure you turn off other items on the circuit before using the AC.

Thanking you..
Epackpolymers.com

The a/c should be on its own circuit.

Originally Posted by Jerry Peck

The a/c should be on its own circuit.

Dimming indicates a loose connection or insufficient wire size for the load. Don't forget there are three wires feeding the breaker box and all need to be check for "tight". A voltmeter is best tool here to check voltages in the main, when the lights are dim, starting at the breakers. Then look at the main line input. When you find a difference you're in the ballpark. It's not uncommon to have a bad connection out on the pole either. Fix IT!

Originally Posted by james hiatt

Dimming indicates a loose connection or insufficient wire size for the load. Don't forget there are three wires feeding the breaker box and all need to be check for "tight". A voltmeter is best tool here to check voltages in the main, when the lights are dim, starting at the breakers. Then look at the main line input. When you find a difference you're in the ballpark. It's not uncommon to have a bad connection out on the pole either. Fix IT!

Typically, dimming lights indicates a bad/poor connection of the neutral and is affected most when 120 volt appliances are turned on or off as 120 volt appliances create an unbalanced load which affects current on the neutral.

Appliances such as the a/c are 240 volt and are balanced loads which have the same amount of current on each phase leg. This can also affect the lights if there is/are bad/poor connections at the phase leg terminals.

In addition to bad/poor connections is the possibility of a bad/deteriorated conductor. This is especially true for underground service laterals more so than for overhead conductors (although I have seen bad conductors in overhead services).

Just some possibilities.