About 3 months ago, I submitted a question about my 3 ton Trane A/C unit that is about 6 years old. The compressor motor would not come on and you advised me to check and replace the capacitor. I replaced the capacitor and the unit has been working fine except that for the last few days I have noticed that sometimes my lights dim momentarily when the unit kicks on. My question is could the initial melted capacitor been a symptom of a bigger problem with the unit?
Thanks,
Stan
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Replies
I hope not. My lights dip slightly every time the a/c comes on, and it's been happening every day for 10 yrs, ever since the house was new.
Do it right, or do it twice.
Have you checked on the unit what rating it needs and on the panel that the breaker is sufficiently large?
If the breaker is not, the draw when starting may be causing your problems. That sometimes will kick that breaker off, but not always.
Easy to fix, get a bigger breaker to match the number on the unit. Sorry if that was discussed before, I can't find that thread.
The breaker must be sized no larger than the feeder wire calls for.
the drop in voltage (dimming lights) is caused by the large starting currentdropping system voltage. this may be caused by too small a wire from the breaker to the load or by too small a wire from the xformer to the breaker, or by bad connections somewhere.
Get an electrivian to come out and test your system. s/he can tell you if you have a problem and what needs to be done to correct it.
SamT
"Law reflects, but in no sense determines the moral worth of a society.... The better the society, the less law there will be. In Heaven, there will be no law, and the lion will lie down with the lamb.... The worse the society, the more law there will be. In Hell, there will be nothing but law, and due process will be meticulously observed."
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Good answer, but I would start with the power company.
If it is a bad connection there is a good chance that it is on the power company's side and if it is an overloaded transformer then again that is their nickle.
Check the requirements on the unit, it will call out the fuse size and start at the panel and check everything to the unit. You might even have a loose mechanical connection at the panel, disconnect, or at the contactor inside the unit. Anyone of these, in addition to the low power supplied by the utility, could be your problem. Occasionally I used to have compressor that seemed to need an extra boost even when everything was correct. Maybe power from the local utility was fluctuating. I would then install a "hard start kit" which was a additional capacitor along with an additional relay, always worked unless the compressor was on it's way out. Higher end units have this as an option to take the load of the unit when starting. Just a thought.
All good advice so far.
Power company can place a recording meter on your service. It will tell them what the amp draw for the whole house is for a week. Motor start up of the unit will be the high amp draw that they record. Look at the the compressor info plate. It should have a LRA (locked rotor amps) number on it. If the poco recording shows you are drawing that amperage when the unit starts look at installing a hard start kit as noneoftheabove suggested.
Loose connections can also cause the symptons you describe, and an inadequate ground can add to them. Another factor that can become cummulative in its affect is unit size. If the unit is more than 25% oversize, it may be short cycling. It doesn't run long enough for the oil to lubricate the cylinders and valves, and leads to premature compressor failure. Depending on the size and type of compressor, the average life for a short cycling unit is about five to seven years. Lack of adequate lubrication= high start up amp draw.
Dave
In addition to all the more qualified advice you have thus far received, I just replaced my thermostat with a White-Rodgers 1F-371 which, amoung other great features, allows me to program a time delay for the air handler fan "on" with respect to the compressor coming "on" (1 to 5 seconds). That, at least, reduces the current draw when both units came on rather simultaneously.
Eric S.