Window a/c tripping breaker on dedicated line

Status
Not open for further replies.
mark32

mark32

Senior Member
Location
Currently in NJ
I ran a dedicated line to a window a/c unit (10 or 12k btu) for a friend and he says it trips the breaker on occasion (once a month). I can't recall what the nameplate said but I know it was under 15 amps. I planned on running this circuit with #12 romex but I came up a few feet short so I used #14 and put it on a 15a breaker. The unit is at least 10 years old and the family has a few pets in the house. I'm thinking this thing needs a good cleaning, owner thinks it trips when the compressor attempts to start when there's still a lot of pressure built up inside. I really don't want to go back in that crawl space again unless I have to.
 
Since it's so old, the compressor is tired and having to work harder is causing a higher inrush.

Fin cleaning might help but in the end the compressor will continue to be worn from time and the previous abuse.

Sometimes with a compressor this size you can hear the wear of it working. If a Good compressor it sounds hard and solid, worn sounds empty and rattlely... This can also reflect
low "freon" but in most casues the Freon all leaves and not a case of a slow leak it leaks out and would burn out the compressor, this is not your case.

A new A/C, good maintaince, good house cleaning, all helps... Just my .02
 
If it was just the dirty fins, that would only make the compressor have to run longer to reach the temperature set point because the cooling efficiency dropped. It doesn't make the compressor pull more amps.

If it trips when the compressor starts, that indicates it is the compressor. It's more likely a combination of an old compressor motor that is getting harder to start, combined with voltage drop caused by the longer starting time pulling high amps on that 14ga wire. Had you run the 12ga it might have forestalled the inevitable for a while longer, but old is old, you can't reverse damage caused by time.

If he can't afford to replace it just yet, you can get what is called a "hard start capacitor unit" that retrofits to the compressor motor. HVAC supply stores sell them over the counter. It's a combination of capacitors and a potential relay to switch them out when the motor gets to speed. That might help, but it might not, it depends on how far gone the compressor already is. But if this is just a window AC unit, it may not be woth the effort.
 
Last edited:
mark32 said:
I ran a dedicated line to a window a/c unit (10 or 12k btu) for a friend and he says it trips the breaker on occasion (once a month). I can't recall what the nameplate said but I know it was under 15 amps. I planned on running this circuit with #12 romex but I came up a few feet short so I used #14 and put it on a 15a breaker. The unit is at least 10 years old and the family has a few pets in the house. I'm thinking this thing needs a good cleaning, owner thinks it trips when the compressor attempts to start when there's still a lot of pressure built up inside. I really don't want to go back in that crawl space again unless I have to.
Click to expand...

What is the maximum fuse or breaker size allowed on the nameplate?
You may be allowed to run it on a 20 amp breaker.
What is minimum circuit ampacity according to nameplate?
 
Consider the cycle times. If the cycle times are short the starting currents will start to continually heat up the thermal element of the breaker until it reaches its tripping point.
The next thing to look at is the shorter cycle time and possible causes. Reviewing the previous posts there are some good points to cpnsider what may be causing short cycling.
 
Window units

Window units

Window units typically have " Rotary " compressors, and when abused they can be known for gettting mechanically tighter and as thus harder to start.
Also modern window ACs, have gone mostly to " blow through " instead of " pull through " condenser coils. This means that the side that gets dirty on the condenser is inside the cabinet, and it must be opened and partially taken down to clean it correctly.
I would not run a 115V Window unit on less than a 20A wall outlet if at all possible.
If you have definite off cycle delay, certain types of Hard Start gear [IE PTC] can be used, but is it worth it on a window AC, maybe not.
I use a recording meter to read inrush AMPS when a degraded compressor is suspected.
An open run capacitor can sometimes be the matter. Many compressors will still start and then later go off on thermal.
Slightly burned or loose compressor terminals, etc can cause hard starts.
Window units typically have a dual run capacitor which covers the condenser fan and the compressor.

All the best.
 
Is someone turning the unit off and then back on right away? Acs as well as domestic refrigerators have a cap tube refrigerant metering device and the pressures have to equalize before the compressor can start.
 
Galt said:
Is someone turning the unit off and then back on right away? Acs as well as domestic refrigerators have a cap tube refrigerant metering device and the pressures have to equalize before the compressor can start.
Click to expand...
Normally the motor overload in the AC will trip first in those circumstances, but that may only happen if there is a 20A breaker on the circuit.
The Minimum Circuit Ampacity specified by the A/C manufacturer (as requested earlier) could shed some light on that. The actual operating amps would be on the order of 10, but would vary with the efficiency of the unit.
A 12,000 BTU window A/C will typically have only a 15A type plug on the end of its cord, but that does not mean that it can operate reliably with only a 15A circuit.
A quick internet search of installation manuals for such units had not turned up an MCA value, but it may be on the label (possibly internal) of the unit itself.

I found this in the manual for a Walmart unit:
IMPORTANT SAFETY INSTRUCTIONS
Be sure the electrical service is adequate for the model you have
chosen.
This information can be found on the serial plate, which
is located on the side of the cabinet and behind the grille.
Click to expand...
 
Last edited:
Hey guys, I thank you for the replies, it's appreciated. So, more than likely the compressor is showing it's age and is drawing more upon startup, which is when it trips. I'm going there on Monday to fix an unrelated problem, I'll take another look at the nameplate but it maybe a moot point because the owner mentioned he may replace it with a larger 240v model in the spring.
 
mark32 said:
Hey guys, I thank you for the replies, it's appreciated. So, more than likely the compressor is showing it's age and is drawing more upon startup, which is when it trips. I'm going there on Monday to fix an unrelated problem, I'll take another look at the nameplate but it maybe a moot point because the owner mentioned he may replace it with a larger 240v model in the spring.
Click to expand...
It saves you a lot of grief when the owner is already leaning in that direction. It save you from selling the owner on some thing that he doesn't want to do.
 
templdl said:
It saves you a lot of grief when the owner is already leaning in that direction. It save you from selling the owner on some thing that he doesn't want to do.
Click to expand...

That's true, the reason I wrote this post is because I was a little bummed that my friend was hinting that he really wanted a 20a line and that this may be the reason for the tripping of the breaker. I knew this unit shouldn't trip the breaker if it were working properly. From the start though, he did say the compressor maybe malfunctioning so it didn't take much to sway him in that direction.
 
mark32 said:
Hey guys, I thank you for the replies, it's appreciated. So, more than likely the compressor is showing it's age and is drawing more upon startup, which is when it trips. I'm going there on Monday to fix an unrelated problem, I'll take another look at the nameplate but it maybe a moot point because the owner mentioned he may replace it with a larger 240v model in the spring.
Click to expand...

Even better because it will probably be more efficient and you'll be able to just change the breaker to a 2-pole and give him the circuit he needs without having to go into the crawl space.
 
jaylectricity said:
Even better because it will probably be more efficient and you'll be able to just change the breaker to a 2-pole and give him the circuit he needs without having to go into the crawl space.
Click to expand...

Right Jay, also, I stopped by this guys house yesterday as noted. The a/c is an older Emerson and the only thing on the unit that says anything about electrical requirements or specs is, "This unit must be plugged into a dedicated circuit". Once home I did a search and found that it's a 12k btu unit and draws 11.2 amps. So my work is done there until he gets the new machine.
 
mark32 said:
Right Jay, also, I stopped by this guys house yesterday as noted. The a/c is an older Emerson and the only thing on the unit that says anything about electrical requirements or specs is, "This unit must be plugged into a dedicated circuit". Once home I did a search and found that it's a 12k btu unit and draws 11.2 amps. So my work is done there until he gets the new machine.
Click to expand...
If it draws 11.2A, it is quite possible that it will not start reliably on a 15A breaker. Since the MCA figure was not supplied, we can only speculate on that.
I agree that an aging motor and compressor might be drawing more that it originally did or starting slower.
 
Starting Current

Starting Current

GoldDigger said:
If it draws 11.2A, it is quite possible that it will not start reliably on a 15A breaker. Since the MCA figure was not supplied, we can only speculate on that.
I agree that an aging motor and compressor might be drawing more that it originally did or starting slower.
Click to expand...

In accord with Gold Diggers note and previous posting, the inrush on this type of inductive load without any kind of " start Assist " which is typical on window AC's can be extreme as read with a recording style amp clamp. I never run any window AC on less than 20A and any HVAC device always go to the max breaker size allowed. This is all because of the nature of the compressor beast. If you have an electronic control on said unit with minimum off cycle of 3-5 minutes, you can install a SUPCO SPP-5 PTC device which will know the inrush current down significantly [after total cleaning of the condenser coil.]
PTCs typically require 5 minutes to recycle. 5 minute off cycle cal also be accomplished with delay on break timer made by ICM, but you'd need a contactor as well. I have serviced and corrected a significant number of jobs where undersized breakers were the only real problem. No doubt you likely have a worn rotary compressor, but its still spins.

All the best
 
Starting Current

Starting Current

GoldDigger said:
If it draws 11.2A, it is quite possible that it will not start reliably on a 15A breaker. Since the MCA figure was not supplied, we can only speculate on that.
I agree that an aging motor and compressor might be drawing more that it originally did or starting slower.
Click to expand...

In accord with Gold Diggers note and previous posting, the inrush on this type of inductive load without any kind of " start Assist " which is typical on window AC's can be extreme as read with a recording style amp clamp. I never run any window AC on less than 20A and any HVAC device always go to the max breaker size allowed. This is all because of the nature of the compressor beast. If you have an electronic control on said unit with minimum off cycle of 3-5 minutes, you can install a SUPCO SPP-5 PTC device which will knock the inrush current down significantly [after total cleaning of the condenser coil.]
PTCs typically require 5 minutes to recycle. 5 minute off cycle cal also be accomplished with delay on break timer made by ICM, but you'd need a contactor as well. I have serviced and corrected a significant number of jobs where undersized breakers were the only real problem. No doubt you likely have a worn rotary compressor, but its still spins.

All the best
 
StarCat said:
In accord with Gold Diggers note and previous posting, the inrush on this type of inductive load without any kind of " start Assist " which is typical on window AC's can be extreme as read with a recording style amp clamp. I never run any window AC on less than 20A and any HVAC device always go to the max breaker size allowed. This is all because of the nature of the compressor beast. If you have an electronic control on said unit with minimum off cycle of 3-5 minutes, you can install a SUPCO SPP-5 PTC device which will knock the inrush current down significantly [after total cleaning of the condenser coil.]
PTCs typically require 5 minutes to recycle. 5 minute off cycle cal also be accomplished with delay on break timer made by ICM, but you'd need a contactor as well. I have serviced and corrected a significant number of jobs where undersized breakers were the only real problem. No doubt you likely have a worn rotary compressor, but its still spins.

All the best
Click to expand...

Some thoughts here-

If you have some kind of "start assist" wouldn't you actually increase the initial demand --- but since you have faster acceleration it would be for less time. Kind of robbing Peter to pay Paul kind of thing.

Also wouldn't a worn compressor have more "slip or leakage" in the compressed media making it actually demand less torque to get it started? Once running it may not perform to original specs and is probably less efficient than it once was but would probably be easier to start. Now if a bearing is what is worn, that will add load, but will also continue to get worse and eventually cause thermal failure of something.

What does having a clean condenser coil have to do with starting current? High pressure in the condenser because of a plugged coil will not happen until it has been running long enough to build such pressure, starting is over with long before this kind of pressure is reached.
 
For 2 or 3 hundred bucks, you can buy a brand new AC unit. How much time and materials would it cost to attempt to fix the old one? By attempt, I mean that it's possible you may try several cures to find out the unit is not repairable.

And if you do manage to fix it for 2 or 3 hundred bucks, they will still have a 10 year old AC unit.
 
K8MHZ said:
For 2 or 3 hundred bucks, you can buy a brand new AC unit. How much time and materials would it cost to attempt to fix the old one? By attempt, I mean that it's possible you may try several cures to find out the unit is not repairable.

And if you do manage to fix it for 2 or 3 hundred bucks, they will still have a 10 year old AC unit.
Click to expand...

And the newer one is going to be more efficient. 10 years newer may not pay off as fast from energy saved as one that is 20-30 years newer though.
 
Status
Not open for further replies.
Top