Dometic Rooftop AC throwing breaker

[yourpcgeek49]

We have a Dometic 59516 rooftop A/C on our 5th wheel trailer. We are currently in Sedona, AZ, but the temp has been hitting 100+. Our A/C will run about 4 hours in the morning and then it will throw the circuit breaker. The compressor in the rooftop unit is way too hot to touch. I have replaced the circuit breaker (it was tripping at 13.5 Amps on a 15 amp circuit.) After letting everything cool off for a couple hours (still in 100 degree afternoon heat) I put a clamp on amp meter on the feed wire and turned on the A/C. It started at 12.5 Amp and gradually increased to over 17.5 amps, then the breaker popped.

 

Is my compressor shot? I would expect that the A/C "should" be able to handle 100 degree temps, even if it had to cycle on & off for thermal protection. Anyone got any great ideas?

[Ray,IN]

Try cleaning the condenser coil and evaporator coil, make sure the plenum is completely sealed between the intake grill and cold air output.

If that doesn't help, then you begin spending money.

Edited June 5, 2016 by RayIN

[Wrknrvr]

Also check your voltage and amperage with a good meter when the compressor is under load. Early in the am to see what the unit is doing before everyone else has there units running also. Also watch the incoming voltage is at the post

Are you on 30 or 50 amp service.

Make sure your water heater is not on electric at the same time. The fan motor may need a little lube at the bearings .

 

Then when everyone else is using there a/c unit what is the voltage. If it gets towards 110 volts or lower then the amps will be going up.

 

It probably is your incoming voltage is the problem. Also you could have a wiring connection problem in your RV.

I think if it is the compressor it would trip the breaker sooner.

 

It could be two thing together that is your problem.

 

I just looked at your post again. If it was tripping your breaker in twenty minutes or less it may be the compressor.

 

Safe travels, Vern

[oldjohnt]

First off I agree with neighbor Ray to clean the coils, and of course that means BOTH the easy to get to Condensor PLUS Evaporator (which some people don't) as well as any interior foam type strip air filters. I use my air compressor plus a soft brush so I don't bend any of the delicate fins. They make a powerful spray coil cleaner I've seen RV AC techs use, but the solution is fairly strong so make sure no spray ends up other then on the coils

 

Next, even if the unit normally draws say 12.5 amps, TO ME THATS TOO MUCH CURRENT FOR A 15 AMP BRANCH CIRCUIT BREAKER (I wouldn't use over 12 amps) and assuming its a Thermal Magnetic Breaker, a long continuous 12 to 13 amp draw could eventually trip the thermal, and of course your reported 17.5 amps will trip it quickly. Id fell better if a 12 to 14 amp unit were on a 20 amp branch circuit then a 15 amp..............

 

While capacitors can go bad, I suspect you unit just has a START Capacitor instead of any START and RUN, so such is NOT my "first" suspect (still anything is possible) .

 

Is the fan motor clean and free, that's easy to see and get to, its not running overly hot is it?????

 

If you clean both coils and the interior air filter and there's no bad capacitor (which I doubt is the problem) and all electrical connections (breaker and panel and at unit) are good yet she still draws 17.5 amps, I think Id have an RV AC Tech take a look as there may be a compressor or Freon problem. Last time I talked to one and he discussed the cost to perform a line tap to check Freon and/or or add any versus the cost of a new unit, I decided to try and check it wasn't worth it since it may fail again and then all that money would be wasted.

 

John T NOT an AC expert or tech by any means, so see what the experts have to say or add to this.................

[Kirk W]

Reading through the responses, most of what I was about to say has been covered. If you have one, I'd use a "clamp on" amp meter to verify what the current load is accurately, if you have not already done so. But this statement: " It started at 12.5 Amp and gradually increased to over 17.5 amps, then the breaker popped." leads me to believe that you have done this. I'm just a little bit surprised that your A/C is on a 15a breaker as most that I'm familiar with are on a 20a but I don't advocate replacing it unless you make sure that the wire size is plenty large enough. Keep in mind that most circuit breakers will only carry about 80% of their rated current for a constant running condition. The A/C should be capable of pretty much constant running if everything is proper, but as Vern has mentioned, low voltage can be the problem and likely is.

 

With resistance loads, as voltage drops the current also drops but that is not true for an ac motor. With such motors what happens is that the power required to turn it does not change and since power is volts times amps, when voltage drops the current must increase and with the increased current the temperature of the motor also increases and so your circuit breaker may very well be preventing the failing of your a/c motors from getting too hot.

[RV_]

Ours did that just before blowing the compressor. However we had had a dead short several weeks before when staying at a friend's place overnight. His extension cord for his 30 amp circuit that he used to hook us up fried and it actually started my surge suppressor on my computer on fire! I ripped it out and threw it outside, no damage at the time. Two weeks later when it got warm enough to need the A/C, the A/C compressor failed. Ours was doing exactly as you describe until it froze. We had to replace the A/C on our second rig as well, but it was a different issue with a badly installed copper high side line rubbing where it went through the shroud and was secured to a sharp hole with no rubber grommet. Blew the charge then a year later failed after we replaced the line and refilled it

[yourpcgeek49]

Thanks everyone for the comments and thoughts. Before starting the A/C the line voltage at our whole house power protector reads 123 V, under load it hovers around 115 - 116 V. Yes, I am using a clamp on amp meter at the breaker box clamping on the AC lead.

 

As I said, it would run for several hours in the morning when the temperature is only 85 - 95 (only???).

 

The coils and fins are clean, but some of the fins have gotten bent (maybe a too low tree branch?) The original breaker was 15A, so I replaced with a new 15A.

 

If anyone has additional ideas, I'd be happy to hear them.

[oldjohnt]

geek49, thanks for the updates:

 

I don't see 123 volts or even 116 under load (if that what it was at the unit itself ????) as low enough to cause current to be 17 amps, so I don't think low voltage (at least as far as at the source) is the problem.

 

I still don't relish the idea of even a perfectly good AC which may draw say 12+ amps being served by a 15 amp branch circuit, since I designed so that no more then 80% of maximum continuous load was allowed, meaning 12 amps max on a 15 amp branch circuit. Subject to actual load and distance and wire size, you could have a voltage drop between where the RV power cord connects and the rooftop AC unit itself AND IF THATS ENOUGH THERE COULD STILL BE LOW VOLTAGE PRESENT AT THE AC UNIT????????????

 

Do you have any idea of what the voltage under load is right at the AC input itself ????????????? If its close to 115 volts you mentioned I wouldn't be too concerned, but if by the time it goes through the RV cord and then distribution panel then maybe 14 gauge wire to the actual AC unit THERE COULD STILL BE A LOW VOLTAGE PROBLEM

 

Its the kind of thing if I were testing it at home Id measure the voltage and current right at the unit as is, and then maybe rig a good heavy short as possible 12 gauge cord from the utility to the AC itself and see what the voltage and current is then??? If its still say 14 to 17 amps and the coils are clean and there's no capacitor or a bad electrical connection problem THEN IM THINKING PERHAPS THE COMPRESSOR IS GOING BAD. Again, carboned loose resistive electrical connections (panel or wiring or AC unit or too small wire) can cause a voltage drop such that at the AC unit itself the voltage is low WHICH IS WHY YOU NEED TO KNOW THE VOLTAGE AND CURRENT RIGHT AT THE UNIT. If the voltage under load is sufficient there, then I'm back to a compressor problem if all else is okay

 

NOTE even if its a perfect new 15 amp thermal magnetic circuit breaker, around 13 to especially the 17 amps you mentioned over a period of time is going to cause the thermal element of the breaker to trip, but real quick when over 15 amps.

 

John T NOT an AC Expert, but still know low voltage or wiring problems or excess line voltage drop (by small wire) or too small of a branch supply circuit can cause excess compressor current flow, as can a bad compressor also............

Edited June 6, 2016 by oldjohnt

[Kirk W]

While bent fins are not a good thing, if only a few then it should not be enough to cause what you have. With voltage of 115/116 that also should not be a factor as it is well within the specifications. You were correct to replace the breaker with the same as was there before the problem began as installing a larger one could prove to be disastrous.

 

The 12.5a sounds pretty much right to me, but we need to figure out why the current is rising as 17.5 is clearly excessive and a 40% current increase is excessive, regardless of the amount of time involved. The issue to be determined is why the increase? Have you monitored the temperatures into and out of the cooling coils? The Δtemp. should by in the range of 18° to 22° or something close to that. If that difference is changing it might give us a clue to what is going on.

[HARY5150]

I have a keystone hideout with a Dometic air conditioner and I am having the same problem works fine any other part of the day except when the temperature start reaching over 100 degrees outside then the inside breaker pops I have put a fan next to the breaker box which seem like it helped a little bit by keeping it cooler but once it got so hot outside nothing seem to stop it from tripping the breaker he sounds like he has the same exact problem is I do

[Kirk W]

This thread is now just over a year old and unfortunately, yourpcgeek49 never returned to share with us what the answer to his problem turned out to be. About all that I can suggest is to read through the above suggestions and see if you find anything of help there. Have you monitored the current drawn to see what it is doing and if it is increasing? How old is the a/c unit we are dealing with? If it has lost some of the refrigerant that might play a part in this difficulty. 

[GlennWest]

Mine did this on a 1 year old unit. Compressor fan motor bad. 

[Charlied]

Air conditioning information on forums is worth what you pay for it. Sometimes less!

 

[D&J]

8 hours ago, Charlied said:

Air conditioning information on forums is worth what you pay for it. Sometimes less!

 

That's why I don't like contributing to this type of thread, I had my own electrical, refrigeration, HVAC buissness for years before I retired so I have real experience and just get tired of information that are just guesses or repeated information people have read on the internet.

Here are some things I know for sure when it comes to troubleshooting this type of problem.

1 If you run a breaker over 80% of its rating for long periods of time it will trip on thermo overload, if you think this is a problem blow a fan on the breaker to cool it.

2 The compressor amp draw will vary depending on the temp of the air comming into the condenser, it is not a set figure, the hotter it is outside the higher the amp draw. If you have damage or blockage to air flow over the condensor you will get high compressor current draw. When checking the condensor you HAVE to remove the cover and look at the inside of the condenser, follow the air flow. If you have any doubt take a hose and flush it out, I made a lot of beer money with a little  water and a hose.

3 A weak run capacitor will cause a high compressor run current, I always had a selection of caps in my truck so it was easy for me to check by changing caps. To actually check one it takes more eqipment than I had so swaping them out worked.

4 Any bad connection will cause resistance and the higher the temp the higher tbe resistance, more current draw.

5 Short of gas will cause compressor high current over time because the compressor uses the returning saturated gas to cool the compressor, if your unit has been running for 20 minutes the suction line (the bigger one) should be cool and sweating at the compressor, sweating if there is enough humidity. Don't touch the small discharge line because it will get a burn. If your unit is running very hot this will not work because the condenser is no longer condensing the gas back into a liquid.

Lots of things to look at when trouble shooting any refigeration system, it was easy for me because I did it every day.

Denny

 

[Charlied]

Me too, 40 years of owning a AC company, wow at the wrong info that comes out of forums. 

[Yarome]

On 7/14/2017 at 9:48 PM, Charlied said:

Air conditioning information on forums is worth what you pay for it. Sometimes less!

 

3 hours ago, Charlied said:

Me too, 40 years of owning a AC company, wow at the wrong info that comes out of forums. 

Instead of taking the time to point out just how little the DYI'er knows, as others have done for you, why not return the favor and contribute something helpful to the OP and the community at large?  Just sayin.... 

Edited July 16, 2017 by Yarome

[D&J]

4 hours ago, Yarome said:

 

Instead of taking the time to point out just how little the DYI'er knows, as others have done for you, why not return the favor and contribute something helpful to the OP and the community at large?  Just sayin.... 

I've tried to tell a good friend we've traveled with for years both by email, texts and phone how to check his unit out, of course he was told just to install the Surpco fix all start cap by all the DYI'ers. I finally had to give up because he knew nothing about how they worked and I didn't want him to get hurt. They still had their front ac so they got by until we meet up with them later that year, it took me 15 minutes to check his unit out and told him his compressor was grounded and we needed a new unit. He was all worried about what he was told by the DYI'ers how hard it wad to change the unit, after we got the parks backhoe to lift the unit on the roof it took 45 minutes and it was running.

I'm just saying there are some things that should be left to people that know what they are doing for safety if nothing else.

Denny 

 

[Kirk W]

1 hour ago, D&J said:

I'm just saying there are some things that should be left to people that know what they are doing for safety if nothing else.

As a service tech for 40 years, I tend to agree with that but there is a lot which many RV owners can do. All that you can do is to give what you believe is the best advice for the person asking and hope that he has the ability to sift out what is valid and what is either wrong or beyond his abilities. Sometimes too much information is just as bad as too little, but you and I can't make that call. I have come to where I stay out of some discussions of issues that I have experience with for those reasons. 

[oldjohnt]

 Yo Kirk FWIW I agree "   All that you can do is to give what you believe is the best advice for the person asking and hope that he has the ability to sift out what is valid and what is either wrong or beyond his abilities."

 

  This interesting thread brings to mind something I've observed over on another Forum for twenty years which I, as an Electrical  Engineer and an Attorney plus a used RV dealer and user over forty years, find it so amusing which is: ANYTIME a question involving Law or Electricity is posed EVERYONE crawls out of the woodwork, EVERYONE is an expert, EVERYONE knows it all and has the perfect correct answer, and it (Electrical or Legal) draws MORE responses then any other topic hands down LOL

 Like the other fine gents here I do my best to provide in depth comprehensive assistance based on my training and experience, maybe its right, maybe its wrong, maybe others agree maybe they disagree BUT WE JUST DO OUR BEST TO HELP and that's not a bad thing in my opinion and why I try to help anytime I can.

 Now its up to the questioner to sort out the BS and good from the bad which can be a challenge lol.  I'm just hesitant to criticize and be unprofessional or impolite to any other persons opinion or answer or methods, its just how I was raised, be courteous and be polite towards others even with those whom we may disagree. What a BORING world it would be if we all thought alike.

 WHO is to judge and be the one who determines what answers are correct or not?????? I'm NOT taking that on lol. Just give it your best honest good faith shot, thats all you can do.

 

 Best wishes and God Bless all here

John T

 

 

Edited July 16, 2017 by oldjohnt

[Jimalberta]

I've been a refrigeration tech doing all types of commercial and industrial refrigeration as well as hvac since 1969. 48 years . I have stopped giving out advice to owners since there are too many variables and too much knowledge and experience needed to be able to diagnose and repair an air conditioner. You need to know what you are doing or damage and injury can occur. 

[rdickinson]

I find myself less inclined to participate in or on this forum for the same reason others have stated.  Dead wrong information.  In other cases I ask a question which is important to me, even directing it to those I know have the experience in that very topic but get no response.  Lastly when someone has a problem which I have had myself perhaps more than once and I go to the trouble to post a step by step response even providing the names of someone in their immediate area who repaired it for me, they keep asking the same question and getting absolutely wrong answers.

It seems sometimes topics of value get poor if any responses and absolutely childish and moronic topics drag on forever.

Re the current post, I had the same problem in Feb, breaker would blow sometimes then it wouldn't cool.  It pulled 29 amps and everyone was off the mark.   The Dometic hot line identified the issue and the unit was replaced by a hotshot tech who wired it wrong.  It cost another 350$ to get it rewired correctly.

Never mind asking the AC questions here, call Dometic and ask them, THEY are the experts.  And don't let some joker sell you a 7 yr old discontinued unit which happened in my case.  Dometic could tell by the serial #.   It still works ok.

Lastly, off topic re putting a hitch on the new 2017 Smarts, It can be done, I did it and have pics. There are adequate fixing points at the rear in spite of what the so called experts say.  Mine was done by a Machinist/ Parts Manager at the Smart car dealer in Victoria.

I have for the most part moved on, finding little value here.

[GlennWest]

Well, please post pictures

[Charlied]

One wire wrong on a capacitor, and the fan won't shut off, even pros mess up, it took me 40 years to learn this trade. you think I can fix your ac in 100 words, no. I offer advice like make sure the condenser is clean and the fins not folded and check that you don't use adapters on the cord. I'm not going to risk having someone that can't even LOOK at the condenser coil and see that it's stopped up, or tell to change a capacitor when I don't even know if they make sure there's no power to the unit, I would rather just be quiet but that didn't really work either.  be safe, check the powers off, go as far as you feel safe, then call a expert. offer him water, have a good ladder and offer to help

[rdickinson]

21 hours ago, GlennWest said:

Well, please post pictures

Of what?

[Yarome]

On 7/20/2017 at 11:42 PM, rdickinson said:

...putting a hitch on the new 2017 Smarts, It can be done, I did it and have pics. 

 

23 hours ago, GlennWest said:

Well, please post pictures

 

1 hour ago, rdickinson said:

Of what?

And apologies to the OP for the hi-jack. Not even REMOTELY related. 

Edited July 22, 2017 by Yarome