15K BTU Dometic A/C tripping breaker

[silverback]

So far I'm not too impressed by the bigger supposedly more AZ friendly Dometic A/C. Yesterday after several hours operation it tripped the 30 A breaker. It is also not doing a very good job cooling the trailer. I have it set to 81 F and it is barely tolerable. It is 90s and more humid up here in Holbrook then normal (almost monsoon season) but we had better operation with our old non thermostat controlled unit. We've got all the awnings unfurled to try and give it some help. Anybody else had this happen?

Enjoying Petrified Forest NP,
K & L

[jcanavera]

Have you checked the voltage available? I 've tripped an outside breaker by having the air, water heater, fridge, and microwave all cranking at the same time. No experience with this type of situation in which you are speaking with my 15K unit.

First check obviously would be that voltage available at the campground box, and also check an outlet in the trailer. I've been in a few parks where on hot days when everybody's units are running, depending on your site in the power loop, the voltage at some sites can drop as low as 95 volts. Low voltage can produce poor cooling results and over heat the compressor, thus causing the breaker to possibly trip.

Also check the output air temp from your unit. It should be 15-20 degrees lower than the inside air temps.

One last check, be sure your fan speed is set to high on the Comfort Control thermostat. If its set to the "auto" mode, the fan will only run at high speed if the difference between the inside air temp and thermostat setting is 10 degrees or more. This is a poor design and can cause inside temps to be uncomfortable since the air conditioner fan is not running at its best cooling mode.

Jack

[silverback]

Jack,
You are the man! We actually read the manual yesterday after the breaker tripped but it didn't register about the fan in auto vs. high (where we have it now). I think we had the perfect storm condition of campground voltage, fan setting, no awnings and heat and humidity. I'll measure AC voltages as soon as I replace the 9V battery in the ($2.00 Harbor Freight special) DVM. It was a lot more crowded here yesterday.
Thanks,
Ken

[john hd]

ken

you are on to something with jack's suggestion.

the wattage of the airconditioner is a constant. if you lower the voltage the amperage goes up!

john

[jcanavera]

I had already done the paragraph on the voltage when I remembered that setting on the thermostat. Normally we run in the auto mode, except when cooling down a hot trailer or when we know the temps are getting pretty hot out there. Personally in that auto setting, the temperature spread between low and high speed ought to be no more than 4 degrees. There's no way a unit can maintain decent inside temps in hot full sun conditions when that fan is running on low speed.

Jack

[john hd]

jack

i agree, i have one of those auto position on my unit. it is much better at keeping the noise down in the trailer than cooling it on a really hot day.

full speed in hot weather is the way to go!

john

[GlenCoombe]

Airstream was pretty ineffective at insulation on the older units ... how are the new units in comparison?
I spent my morning sanding the roof of my coach in preparation for the first coat of white polyurethane to go on tomorrow. I'm hoping the combination of the high reflectivity white on the center section of the roof and the new dark tint on the windows will help the A/C to do a more effective job.
It's been pretty hot in the Carolinas this year so far....

[bhayden]

I've wondered about white vs. shiny aluminum as far as reflecting heat. My first guess would be a mirror finish would be better at reflecting heat but I'm not sure. Aluminum reflects the visible light spectrum but maybe not in the IR?

Shade for sure is a biggy. Might want to reverse the direction of the trailer morning and evening to keep off the most sun. And/or rig auxillary awenings with tarps if possible.

I've read it's important for the AC to cycle to prevent it from freezing up. I've seen this condition on a couple of occasions at work where ice has formed on the coils and it creates a run away condition where the AC compressor is running full tilt and the ice just forms a solid block preventing any heat transfer. If the drain stops dripping water this could be happening.

[jcanavera]

Originally Posted by bhayden

I've wondered about white vs. shiny aluminum as far as reflecting heat. My first guess would be a mirror finish would be better at reflecting heat but I'm not sure. Aluminum reflects the visible light spectrum but maybe not in the IR?

.

I can tell you from a real life camping trip that white is better. Two trailers side by side facing the same direction in full sun both using 13.5 K Duo-Therm A/C units. The SOB has a Brisk Air model, the Airstream has a Penguin. Available power is equivalent, outside air temperature is 100 degrees. Both trailers have a curb side awing extended. All curtains and blinds are closed, neither trailer has any skylights. Both have front and rear vent hatches. The white SOB is 28', the Airstream is 27'. The white SOB was 8 degrees cooler than the Airstream.

That's the trip where I learned that Aluminum (even with a white roof) absorbs a lot of heat.

Jack

[GlenCoombe]

BHayden, I'm going for the white on the very top of the coach for now. No awnings, shade is not always possible as the customers door is where I try to park. Some golf clubs do have shade close to the front door and I'll take advantage of it everytime I can. I'm going to take a temp reading of the skin with a laser thermometer when it's complete just for a comparisson.
Jack, did the SOB have more insulation in the roof? My old Coachman had a thicker roof and was much easier to cool with a smaller a/c unit.
Today it was a solid 4 hours on the ladder. Started as soon as the dew was dry... taped the seams along the rivet line and began the brushwork of applying the poloyurethane. I'm now recovering and taking drugs...resting up for the days work tomorrow.
Gotta wet sand and then do coat number two. If my body holds up I'll end up with three coats, and some new muscles to show for the effort. My kingdom for an air compressor.

[Jim Clark]

Originally Posted by bhayden

I've wondered about white vs. shiny aluminum as far as reflecting heat. My first guess would be a mirror finish would be better at reflecting heat but I'm not sure. Aluminum reflects the visible light spectrum but maybe not in the IR?

Shade for sure is a biggy. Might want to reverse the direction of the trailer morning and evening to keep off the most sun. And/or rig auxillary awenings with tarps if possible.

I've read it's important for the AC to cycle to prevent it from freezing up. I've seen this condition on a couple of occasions at work where ice has formed on the coils and it creates a run away condition where the AC compressor is running full tilt and the ice just forms a solid block preventing any heat transfer. If the drain stops dripping water this could be happening.

I believe freezing up is a sign of a unit which is short on gas or dirty. You want a good sweat back on the suction line, which is the bigger one also called the low pressure line. I know my unit is working great when I seen the condensation coming down the drain tube and pooling on the ground. Same for my home unit.

Jim

[lewster]

As the outside ambient temperature rises, the A/C unit actually draws more amps, as it is working harder. There is a formula that I can dig up in my tech notes if anyone is interested. When we check the amp load for proper operation, we always re-calculate the run amp load based on the outside temps and adjust it accordingly.

[jcanavera]

Originally Posted by GlenCoombe

.
Jack, did the SOB have more insulation in the roof? My old Coachman had a thicker roof and was much easier to cool with a smaller a/c unit.

I'm not sure what my SOB had for insulation in the ceiling, although I know it was some type of batting. I know the walls were not insulated that great because I remember it was very easy to hear my neighbors talking outside the trailer. My Classic is much quieter.

The SOB roof was plywood covered by a rubber membraine. I had ducted air in the ceiling.

Jack

[bhayden]

Originally Posted by jcanavera

I'm not sure what my SOB had for insulation in the ceiling, The SOB roof was plywood covered by a rubber membraine. I had ducted air in the ceiling.

Mmm, plywood could well be the difference. Wood is a wonderful material (until it rots ) Aluminum is a great conductor of heat so the skin riveted to aluminum ribs to a aluminum interior panels might be acting like aluminum cookware. I'd have to do more research but it seems to me aluminum actually reflects IR heat away which is why foil faced insulation is used. It will be an interesting experiment. However, a ruberized white coating is likely to provide a different result than white enamal paint becuase of the different thermal coefficient.

Someone want to try a cedar shakes

-Bernie

[Barry2952]

The major function of AC is to remove humidity. The human body can tolerate and feel more comfortable in higher temperatures if the humidity is low.

Many people will try to cool a home or trailer after leaving the unit off for a period of time to save money. Economically, you are better off leaving the AC on all the time, on a thermostat. This will draw the humidity in the space out of the wood, furniture and other belongings and allow you to be comfortable at a higher temperature setting.

When I rebuilt my toybox I sprayed 2"-3" of structural foam into all the wall and ceiling cavaties and now it's like a Thermos.

BTW, your circuit breaker could be defective. They are simply a electro-mechanical device that can become sensetive after being tripped a couple of times. CB replacement resolves most AC issues. If the new CB trips, look further. Never install a CB that is higher in ampacity than the wre size will allow. 15-amps for 14-gauge, 20-amps for 12-gauge and 30-amps for 10-gauge. The allowable wattages are 1320, 2000 and 3000 respectively.

[lewster]

Originally Posted by Barry2952

The major function of AC is to remove humidity. The human body can tolerate and feel more comfortable in higher temperatures if the humidity is low.

Many people will try to cool a home or trailer after leaving the unit off for a period of time to save money. Economically, you are better off leaving the AC on all the time, on a thermostat. This will draw the humidity in the space out of the wood, furniture and other belongings and allow you to be comfortable at a higher temperature setting.

When I rebuilt my toybox I sprayed 2"-3" of structural foam into all the wall and ceiling cavaties and now it's like a Thermos.

BTW, your circuit breaker could be defective. They are simply a electro-mechanical device that can become sensetive after being tripped a couple of times. CB replacement resolves most AC issues. If the new CB trips, look further. Never install a CB that is higher in ampacity than the wre size will allow. 15-amps for 14-gauge, 20-amps for 12-gauge and 30-amps for 10-gauge. The allowable wattages are 1320, 2000 and 3000 respectively.

Not to be a 'nit-pick' here, but wattage is figured as P=IE, so you multiply volts (120) X amps to get the allowable wattage for a circuit. 15 amp lines allow 1800 watts, 20 amp lines allow 2400 watts and 30 amp lines allow 3600 watts.

[Mike Lewis]

Originally Posted by Jim Clark

I believe freezing up is a sign of a unit which is short on gas or dirty. You want a good sweat back on the suction line, which is the bigger one also called the low pressure line. I know my unit is working great when I seen the condensation coming down the drain tube and pooling on the ground. Same for my home unit.

Jim

Freezing ocurs when the moist air passes through an evaporator that has below freezing temps. The moisture freezes to the evap. and blocks air flow. This condition is common when the thermostate is set to low and operating in very humid conditions.The easiest way to prevent freezing is to raise the thermostate setting.---pieman

[jcanavera]

Originally Posted by Mike Lewis

Freezing ocurs when the moist air passes through an evaporator that has below freezing temps. The moisture freezes to the evap. and blocks air flow. This condition is common when the thermostate is set to low and operating in very humid conditions.The easiest way to prevent freezing is to raise the thermostate setting.---pieman

....and make sure that fan speed is up. Dirty air filters or too slow an air speed will tend to allow ice to form.

Jack

[Barry2952]

Originally Posted by lewster

Not to be a 'nit-pick' here, but wattage is figured as P=IE, so you multiply volts (120) X amps to get the allowable wattage for a circuit. 15 amp lines allow 1800 watts, 20 amp lines allow 2400 watts and 30 amp lines allow 3600 watts.

That would be true, if you were not an electrician, which I am. The rule of thumb is that you should never load a circuit in excess of 80% of its capacity. I like to use 75%, but then I'm a cautious person.

In addition, should voltage be 110 volts there is a proportional decrease in the capacity of the circuit. Your formula does not allow for voltage fluctuations, which I'm sure we've all experienced.

[firefly007]

Originally Posted by Barry2952

That would be true, if you were not an electrician, which I am. The rule of thumb is that you should never load a circuit in excess of 80% of its capacity. I like to use 75%, but then I'm a cautious person.

In addition, should voltage be 110 volts there is a proportional decrease in the capacity of the circuit. Your formula does not allow for voltage fluctuations, which I'm sure we've all experienced.

Hey Guys, I'll have to crack the books to be sure but I think when dealing with inductance devices like ac motors the formula is P=IE times the cosine of Theta which would be the phase angle of the windings.

Whew, I usually just tear about 10 percent off the top of the P=IE formula or measure the actual current in amps. There are several small inline Amp/Watt gauges that look like a short extension cord. I like to keep one in the trailer to keep an eye on Watt (sorry) is going on. If anyone needs one I will post the source.

Steve