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Old 04-20-2015, 06:18 AM   #1
Little Guy
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A/C performance

What should I expect from the AC unit in our 2012 30' Laredo TT? The ac will lower the inside temp approx. 10 to 12 deg from the outside temps. When it is 95 deg outside, it will be 85 deg inside. If we start out behind the curve so to speak, by not starting the ac soon enough, we are lucky to be able to maintain the same temp as outside. We keep the shades down and try to utilize the awning to help shade "Larry". I was hoping for additional cooling performance. Am I expecting too much from our 1 ac unit? On a few occasions, the ac unit will fail to start and has to "rest' for a while before it will kick in. Maybe a weak capacitor or something. Lucky for us that the nights were still cool enough to sleep comfortably in Bullhead City/Laughlin.
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Old 04-20-2015, 11:24 AM   #2
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In 2009, parked under a tree in June at that city I call HE.., I was lucky to see 80 degrees at night and about 90 during the day. It never shut off for the three nights we were there and daytime temps were about 115.

I am under the impression that if the A/C can produce air 20 degrees cooler than ambient it is working. If your trailer is in the sun, it's like a giant oven soaking up the heat while the A/C tried to cool it off. When we test them we use a thermometer with two probes. One is on the counter and the other is in the discharge at the A/C. If we get 20* drop then we call it good.

You may want to test the air temp at the unit and if it's not 20* colder, then you might need to start looking for problems. Take the cover off the roof portion and inspect the coils for any airflow issues. Also pull the filter and look at the return ducting. It should be sealed on the sides so the A/C isn't pulling air from the rafters.
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Old 04-20-2015, 12:37 PM   #3
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Keep the AC on when you know its going to be warm. If you get too much of a load on it, it'll run non stop. And yes, a 20 degree temp drop is the standard. Unless you start the AC right away, it'll never catch up. It has to remove the humidity before it can cool the air.
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Old 04-20-2015, 02:31 PM   #4
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After you determine that your AC is in fact operating properly you may want to seriously consider adding a 2nd AC if you're going to spend much time in places like Bullhead City and Laughlin. When I bought our new trailer in 2014 I knew we would probably be staying in some pretty hot places so had a 2nd AC added up front. The main 15k in the living area and the 13.5k in the bedroom do a pretty good job of keeping up in our 319RLS.
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Old 04-20-2015, 03:16 PM   #5
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The Delta between the outside temperature and the inside temperature is irrelevant. Yes, heat radiates in through the roof and walls, but that is not factored in when looking at the operation or efficiency of the unit. The 20 degrees often referenced is the difference between the supply and the return air. 20 degrees is optimum, but 16-18 is acceptable. You can insure optimal performance from the AC by keeping the filters clean and making sure that the plenum and duct around the discharge grills are taped properly and that you are not pumping cold air into the ceiling.
Incorrect harge is very unusual on these units because they are charged at the factory through a process stub and then it is cut and welded, so there is no way for freon to get on or out except from a leak(uncommon) or soldering in a service port. Correct refrigerant charge can be determined using a clamp on meter to measure the amp draw of the compressor.

Solar screens also help. My Outback 277RL with one AC stays cool and cycles on and off in the Central Texas July sun, so if you are not getting the proper cooling, there are things that need to be checked.
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Old 04-20-2015, 03:20 PM   #6
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Originally Posted by scott24 View Post
Keep the AC on when you know its going to be warm. If you get too much of a load on it, it'll run non stop. And yes, a 20 degree temp drop is the standard. Unless you start the AC right away, it'll never catch up. It has to remove the humidity before it can cool the air.
That is not correct. The dehumidifying begins as soon as the unit is turned on and continues the entire time it is running. It only takes a couple of minutes for water to begin collecting on the coil. That is why water constantly drips off your roof when the unit is running.
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Old 04-20-2015, 03:37 PM   #7
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That is not correct. The dehumidifying begins as soon as the unit is turned on and continues the entire time it is running. It only takes a couple of minutes for water to begin collecting on the coil. That is why water constantly drips off your roof when the unit is running.
If there's no condensation on the coil then there's an airflow issue or he's low on charge. Leaks are not uncommon. The proper way to check charge is either subcooling or superheat. Not an amp draw. If his indoor temp is 90 and he cant get a supply air temp of at least 75, something is seriously wrong.
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Old 04-20-2015, 04:04 PM   #8
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If there's no condensation on the coil then there's an airflow issue or he's low on charge. Leaks are not uncommon. The proper way to check charge is either subcooling or superheat. Not an amp draw. If his indoor temp is 90 and he cant get a supply air temp of at least 75, something is seriously wrong.
Those are both accurate ways to check charge, however, both require that you connect gauges and without installing a service port there is no way. When you install the port, then you don't know if it was charged correctly because you have lost the charge.
That is why Dometic recommends checking by compressor amp draw. The compressor draw on the data plate is based on 95 degree ambient(outside) temperature. You will get a one amp difference in draw either up or down with every 10 degree change in ambient temp. If the data plate says 10A then if the ambient temp is 105 degrees, then the compressor amp draw, with correct charge, would be 11A and 10.5A for an outside temp of 100 degrees. . This is from Dometic, not me.This also applies to he Coleman rooftop units. This eliminates having to connect with a piercing valve, after which you would have to evacuate, fix the hole and then recharge and there is no reason to do that if you can check it without breaking into the system.
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Old 04-20-2015, 04:19 PM   #9
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We have not camped where it is too hot all the time but have had weeks in the 90's from time to time. We turn the AC in right away and hope for the best. The first night might be a little warm but by morning it seems to be cool and once we get it low we leave it there and hope it maintains for the day. It will be warmer at 5 PM than it was at 8 AM but that is fine. We leave it set in the 60's and just run it. If it is that hit we will run the water heater on gas to avoid voltage issues.
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Old 04-20-2015, 04:20 PM   #10
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Originally Posted by Bob Landry View Post
Those are both accurate ways to check charge, however, both require that you connect gauges and without installing a service port there is no way. When you install the port, then you don't know if it was charged correctly because you have lost the charge.
That is why Dometic recommends checking by compressor amp draw. The compressor draw on the data plate is based on 95 degree ambient(outside) temperature. You will get a one amp difference in draw either up or down with every 10 degree change in ambient temp. If the data plate says 10A then if the ambient temp is 105 degrees, then the compressor amp draw, with correct charge, would be 11A and 10.5A for an outside temp of 100 degrees. . This is from Dometic, not me.This also applies to he Coleman rooftop units. This eliminates having to connect with a piercing valve, after which you would have to evacuate, fix the hole and then recharge and there is no reason to do that if you can check it without breaking into the system.
To me that's not very scientific way to check. Too many variables, bad TXV, restricted orfice or cap tubes. To me they leave out too many things. Myself I have the equipment to check everything....oh well, thats what makes this world go round. I didn't mean anything personal an I hope you didn't take it that way. Enjoy the upcoming camping season Bob!
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Old 04-20-2015, 06:09 PM   #11
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This has helped us when we come back to our trailer and it is up in the 90 degree range and the AC has not been left running we open the vents on the bottom of the AC so it does not try to cool the trailer by first blowing air through the oven hot ceiling ducts. There is only so much insulation on those ducts so the ducts are going to heat the cooling air the AC is sending through them. When it is really hot, cool the main room the AC is in and then close the AC vents and allow it to cool the attic ducts and the rest of the trailer.
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Old 04-20-2015, 11:11 PM   #12
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I did the same as sourdough I had a 2 ac added when I bought my 2014 cougar since I live In south Louisiana
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Old 04-21-2015, 03:53 PM   #13
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To me that's not very scientific way to check. Too many variables, bad TXV, restricted orfice or cap tubes. To me they leave out too many things. Myself I have the equipment to check everything....oh well, thats what makes this world go round. I didn't mean anything personal an I hope you didn't take it that way. Enjoy the upcoming camping season Bob!
No offense taken. I've been doing marine AC for close to 20 years and I also have all of the equipment, but the amp method is an easy way to see if charge is in the ballpark without having to break into a sealed system and start from scratch. Yes, it does leave some variables, but when you can not connect gauges, the options are somewhat reduced.
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Old 04-21-2015, 04:32 PM   #14
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Interesting thread to read. Yesterday the temp inside in direct sunlight was 90, the AC brought it down to 65 which I thought was pretty chilly compared to sitting outside.
A must do is to clean filters and climb on the roof and do a inspection and cleaning.
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Old 04-21-2015, 06:52 PM   #15
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Thanks for all of the information. Your input is valuable and appreciated.
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