OK, electrician Dopers, here’s a quiz…I live in a somewhat old apartment “house” in the basement apartment, and my window A/C unit tends to blow the circuit breaker after about 20 minutes of use. Is this more likely to be a problem with the A/C unit or the electrical system in the apartment? I’m going to have the landlord check it out, just curious to hear from the electrically adept on SDMB on this.
My A/C unit did this about a month ago. Turned out to be a bad circuit breaker. If you have access to a clamp type amp meter, you could measure the current at the circuit breaker. Check it against the current rating located on the unit. If the current is within specs and the breaker is still tripping, then just replace it.
IMHO, if the breaker is tripping after some use instead of right at startup, then it is prolly just the breaker but check it just to be sure.
Most likely the problem is in the apartment’s wiring. And problem is a harsh term. In an older apartment, the odds are good that there are other outlets on that same circuit breaker. An air conditioner has a strong current draw and needs to be the only device on the breaker.
Next time the breaker blows, look around your apartment for anything that has suddenly stopped working – refrigerators, clock radios, hair dryers.
Also, check the specs on your air conditioner. If it’s drawing 20Amps and your breaker is only 15Amps, that could be the cause. Maybe getting a smaller unit would help.
Indeed. The AC should probably have it’s own dedicated circuit, especially if it’s an add-on appliance. A common way to* add a circuit is to run a line from the main panel to a junction box (or a disconnect), then run a line from that to the AC unit.
*Add “have a licensed Electrician” here.
We don’t have enough information to know. It’s a SWAG.
First, you need an HVAC tech, not an electrician. (even if it’s an electrical problem, the HVAC tech will be much better quailified to diagnose this)
The problems could be:
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Too many current drawing devices on that circuit. While a “dedicated” circuit is preferred, it is not too common on 115V units. If your unit is 220V, it’s probably on a dedicated outlet already. After the breaker blows, go around and see what other outlets (or lights/appliances) are dead also. That will let you know what other outlets/appliances are on that circuit. When you turn the window unit back on, turn off the other appliances on that circuit. (and see it it still trips after 20 minutes) You may simply have too many things on that circuit.
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A dirty condenser coil on the A/C unit. Slide the unit out (after unplugging it) and see if the coils are clean.
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A failing compressor. If the unit is older, it may be losing lubrication and going into a slow death spiral. (which it will not recover from; and the unit will be replaced)
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A loose wire, either in the plug, recepticle or breaker box. A loose wire will cause current to surge. Tighten.
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An undersized breaker. This is not as easy as putting in a bigger breaker. 15 amp breaker for 14 ga wire; 20 amp breaker for 12 ga wire. The breaker must be sized correctly, or you’ll create a fire hazard.
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A failing breaker Not uncommon. It should trip at around 80% of it’s rated load. As UncleRojelio noted, a qualified HVAC tech or electrician will be able to put an Amprobe on the wire to see at what current the breaker is tripping.
Older systems were fitted with regular and HACR (Heating air conditioning refrigeration) breakers, although most every breaker now is HACR rated.
That being said, an amp clamp is your best diagnostic tool.
thanks so much for your replies, I am going to make sure that all of the relevant factors are accounted for!
Might try cleaning the filters too, if they’re too bad that will cause problems.