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Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 10479
Experience:  RVDA/RVIA Master Certified Technician with many years experience.
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2015 rv with 13,500 rooftop unit with heat strip manual

Customer Question

2015 rv with 13,500 rooftop unit with heat strip manual control switches. unit on a 20 amp breaker using 4000 watt generator starts then trips generator breaker in a few minutes. I am confused about the 2 knobs (how to set for a/c only and or set for heat strip only) ron/Indiana.
Submitted: 8 months ago.
Category: RV
Expert:  Randall replied 8 months ago.

Do you have the water heater on AC mode? That is the usual cause of this OR some other AC use that is overloading the circuit.

Customer: replied 8 months ago.
ac unit in a cargo trailer no water heater. has 2 wall outlets on 15 amp breakers but not using them at same time.
Expert:  Randall replied 8 months ago.

Are you starting this on high fan and then moving to high cool after a few minutes?

Customer: replied 8 months ago.
the 2 switches confuse me about what I am setting them on have you seen these controls on one of these dometic units
Expert:  Randall replied 8 months ago.

Yes.........and they are usually marked clearly as to "Hi Fan", Lo Fan", High Cool, and Lo Cool and "Heat" if you have a heat strip. No manual for this?

Customer: replied 8 months ago.
bought this trailer used 1 yr old did not receive operating manual. dealers service guy has been no help. it is 100 degrees where I am using the trailer. need to get this solved or take the trailer back to dealer for a refund(lol).
Expert:  Randall replied 8 months ago.

Can you attach a photo of the controls to your post so I can see them?

Customer: replied 8 months ago.
I am set up at a tractor/steam engine show as a vendor. unhooked trailer and left it at my booth for tonight and drove home. I can take photo with my smart phone tomorrow but don't know if I can attach to these messages. could text it to your phone number tomorrow am when I get back to the show. I have never seen controls that I could not figure out like these.
Expert:  Randall replied 8 months ago.

Is this a Coleman or a Dometic A/c?

Customer: replied 8 months ago.
it is a dometic installed as a option on a Bravo cargo trailer at factory along with the electric breaker wiring set up.
Expert:  Randall replied 8 months ago.

Did they wire this up on a 20 amp breaker and use #12 wire or do you know?

Customer: replied 8 months ago.
main breaker is 30 amp with separate breakers for this a/c (20amp) and florescent lights on a 15 amp plus 2 wall outlets on 15 amp and outside work lights(quartz-heavy draw). I do not use other things while using the a/c(I know better) I have to assume they used the proper gage wiring.
Expert:  Randall replied 8 months ago.

Take a look at the attached link and tell me if this is your control panel. http://www.ebay.com/itm/Dometic-3310741-016-Polar-White-Non-Ducted-Manual-Air-Conditioner-Controls-AC-/131402789205

Expert:  Randall replied 8 months ago.

You would be surprised at how often this gets messed up by these specialized vendors. You can check by going to the breaker and see what wire size is coming out of there.

Customer: replied 8 months ago.
went to link it is not that model it looks more like the 79.00 distribution cover.
Expert:  Randall replied 8 months ago.

Attach a photo of those tomorrow if you can and I will try to get one from my shop so I can this up close.

Customer: replied 8 months ago.
ok will do.
Expert:  Randall replied 8 months ago.

10-4

Expert:  Randall replied 8 months ago.

Just checking back in to see if you were able to resolve this issue or do you still need some additional input from me here?

Customer: replied 8 months ago.
sorry I have been busy with other things but now need to get back to my a/c problem. I thought I had the control knob setting problem figured out but I ran into another little problem. Had a/c running for a hour and cooling trailer just fine. Decided to flip on the 15amp breaker for the florescent celing lights(2 fixtures don't know how many bulbs or wattage of bulbs(THOUGHT THEY WOULDN'T DRAW MUCH) wrong thinking but they stayed lit for about 20 min. before tripping the generator's breaker. Since I have no way to contact Dometic I can not know how much the a/c draws. sometimes when a/c running, generator sounds as it is running faster as if load taken off. this event does not trip gen. breaker and in a few minutes it sounds like load is back on. I am wondering if the a/c unit needs more than a 20amp breaker? If so what would be involved?
Expert:  Randall replied 8 months ago.

Lights like that don't draw much. Chances are your water heater is on AC mode. Turn that to LP mode and your fridge to LP mode to save power. As the ambient temps rise, so does the power consumption on the A/C. It can draw an additional 5 or 6 amps on a very hot day.

Expert:  Randall replied 8 months ago.

Shade the A/C if you can to reduce the ambient temps AT the unit. That can save you several hundred watts.

Customer: replied 8 months ago.
this is not a rv and has no water heater. we were operating in very hot conditions with no shade available. we do not yet have a fridge but when we can find the one we want it will be a small dorm room type and we will want to plug into one of the 2 double outlets that are a part of this cargo trailer turned into a modified toy hauler(we set up at festivals and vend merchandise no toys hauled) both of the 2 wall outlets are on 1 15amp breaker and I am beginning to suspect that they might give me problems too. the only other things we might plug in would be a coffee maker and(by turning off the a/c) we would use a small microwave for a short while.
Expert:  Randall replied 8 months ago.

How big is the generator here? Most units can't support any microwave use when the A/C is running. Even a small one uses about 800 watts. Did someone wire up the trailer for AC uses? I am wondering if they used the wrong wire sizes or breakers? Do you know what those are here?

Expert:  Randall replied 8 months ago.

I see we convered part of this before...........had to go back and re-read some of what was discussed. 4K should work here, but no other big draws. How many watts are the lights each? It might be the wire size here. We need to find that out.

Expert:  Randall replied 8 months ago.

Keep in mind that 30 amp under ideal conditions (120 VAC input) gives you 3600 watts of power. AC on a real hot day can use almost 20 amps or 2400 watts. If the input AC voltage is lower, the amount of watts drops as well. Add up the uses. See what that total is and let me know.

Expert:  Randall replied 8 months ago.

Just checking back in to see if you were able to resolve this issue or do you still need some additional input from me here?

Customer: replied 8 months ago.
will try to check wire size on lights today. generator is a 4000 watt start but running output not listed in manual and cannot find on line. e mailed mfgr to try to find out but other 4000 watt gen's show 3500 running. also calling dometic for watt draw on start and running. if need be I can shut off a/c while using lights(has 2 dome lights powered by tow veh.) also fyi the breaker shows a 30amp main plus a 20amp for ac and 3 15 amp breakers-1 for 2 2plug outlets, 1 for flourscent lights, and 1 for outside quartz lights(will never use these) may even remove flourescents as I don't really need them. will gather all info and get back to you-thanks for your patience.
Expert:  Randall replied 8 months ago.

What is the make of your generator? You might be able to upgrade to a slightly larger unit and solve this. No hurry.......just wanted you to know I was here if you needed more.

Customer: replied 8 months ago.
generator is a sigma sg4000 from rural king and cannot be returned.
Expert:  Randall replied 8 months ago.

Sell it and get a good unit. Generac makes some good ones. Get at least a 5K unit and best with electric starter. That would save you some headaches now and down the road.

Expert:  Randall replied 8 months ago.

Hopefully, you got this resolved as I didn't hear back from you. You can always return to this posting again if you Bookmark it and we can do a follow up. All part of our service and please take time to enter a rating as that is the only way I get credit for my time spent helping you. Thanks! Be safe........