Long story short, I bought a new 5th wheel and paid to have a second AC installed. The ducts run from the bunk house to the front bedroom and I specified a 15,000 BTU connected to the existing duct work so that the increased capacity would be available to all parts of the trailer and not just the bedroom.The dealer made a mistake and installed a 13,500 BTU and not the 15,000. So far they appear to be willing to help resolve the issue since I discovered it after some minor wiring glitches had to be tracked down. The selling dealer is not local nor convenient.They are saying the Dometic rep is telling them that they don't recommend ducting a second 15000BTU AC as it will cause the evaporator to ice up. They are also saying that ducting a 13,500 "makes it 15,000" BTU.Now, I'm no expert here. The rating of BTU is the capacity for heat transfer which I see as a function of the compressor and evaporator sizing and not affected by ducting or not ducting.I'm trying to be a reasonable consumer and work with these folks and would like your expert opinion on the use of 2 15K units versus 1 15K and 1 13.5K. Remember this is deep South Texas where summer camping means high humidity and nearly 100 degree heat with regularity from June through September.Thanks in advance for your advice.

There may be something to that, as Monaco would only install 2 13.5 heat pump/AC on a 40' ducted system and those we know that have traded out, say that no dealer would install 2 15's on the duct system, only one 15 & one 13.5. I do know that the two 13.5 will just barley keep the 40' motorhome comfortable during the summer in south Texas(Pearsall). I am sure that one of each will keep your 5er comfortable. Just ask for proper compensation for the mistake and see how the summer goes.

You don't say how big your trailer is. Mine is 36' and has the same AC configure as you. Bedroom AC is not tied in to the ducting. We've had no problem with it keeping the trailer cool, including in Las Vegas and eastern Oklahoma in the summer time. We just leave the bedroom door open. The thermostat for the main AC is generally set at 68. If I remember correctly, the compressors even cycle off from time to time. I have redone the insulation under the trailer and I ordered it with double pane windows. I don't know how much that contributes to keeping it cool, but it can't hurt.

I have two ducted 15k low profile Coleman Mach AC's on my 5th wheel.I have had no issues with icing, or anything else, running them at the same time.Unless the Dometics are radically different, I doubt the info they've told you is accurate.

Thanks for the note. The trailer is 41 1/2 feet full profile. Maybe asking to speak directly to the Dometic rep is advisable.

The difference from adding the 15k BTU and the 13.5k BTU air conditioner is only 5% of the total capacity and then concentrated in the bedroom. It is not enough to worry about.

13,500 BTU vs 15,000 BTU second AC | Good Sam Community

The_Texan
Explorer
Aug 05, 2013
dougrainer wrote:
The Texan wrote:
dougrainer wrote:
The Texan wrote:
We are running BOTH 13.5 units on 30A with NO problems, so you will have no problem with a 15 unit. Try running your fan on "high" instead of auto, when in high humidity and that should stop the icing.

Really??? If you look at his photo post, his 13.5 Penguin will pull 15.1 amps at 95 degree ambient on hi cool. His 15k original rear unit will pull 16.1 amps on hi cool at 95 degrees. That puts his TOTAL AC load at 31.2 amps with NOTHING else in his RV on. If the temps go to 105 (they are in Texas right now), his amp draw will go UP 2 more amps to a total of 33.2 amps. Doug
Doug, go back and read his post. He said ONE 15k on 30A, NOTHING about running both on 30A. And like I said we are setting here with temps reaching low 90s and have no problems with two 13.5k Dometic on 30A. Yes, we do shut down the rear AC when we run the micro and we do have the water heater on gas, but we have a residential fridge, a 32" TV and all the other normal stuff. We have NOT tripped a ckt breaker once.

NO, YOU read it again. I see nothing in his post about running his RV on 30 amp service. YOU made the statement about your RV on 30 amp service and I was just letting him know, that almost ALL RV's cannot run 2 AC units on 30 amp service especially his. I will bet if I look at your 50 to 30 adapter, it is burnt and corroded (30 amp side) from the excess amp draw caused by what you are doing. Doug
Sorry Doug, but I hold a Journeyman Electrician license and I will guarantee you my dogbone is NOT burnt or corroded. I know what my system is doing at all times and with BOTH 13.5 Dometic AC's running, even when they both have a compressor start at the same time, it does NOT exceed 30A.

Here is his post I referred to, that you say did NOT exist...
TexasRedNeck wrote:
Regarding the 30 vs 50 amp, I will use 50 amp sites until the fall and hope that 30 amp will run the 15K unit in the main living area and be enough without cranking up the second AC. I think the 15k AC pulls about 17A at start up if I recall correctly.
CyberSanford
Explorer
Aug 08, 2013
Thanks DougRainer

I was told by my original installer about turning the thermostat back a little. I just thought this ac was built to run and to turn back the temp kinda defeats the purpose of getting it cold inside. But I guess if I have to.
So do you think I had a choice regarding the freeze control device? Did I need to ask for that?
thanks
Mark
dougrainer
Nomad
Aug 08, 2013
The Texan wrote:
dougrainer wrote:
The Texan wrote:
dougrainer wrote:
The Texan wrote:
We are running BOTH 13.5 units on 30A with NO problems, so you will have no problem with a 15 unit. Try running your fan on "high" instead of auto, when in high humidity and that should stop the icing.

Really??? If you look at his photo post, his 13.5 Penguin will pull 15.1 amps at 95 degree ambient on hi cool. His 15k original rear unit will pull 16.1 amps on hi cool at 95 degrees. That puts his TOTAL AC load at 31.2 amps with NOTHING else in his RV on. If the temps go to 105 (they are in Texas right now), his amp draw will go UP 2 more amps to a total of 33.2 amps. Doug
Doug, go back and read his post. He said ONE 15k on 30A, NOTHING about running both on 30A. And like I said we are setting here with temps reaching low 90s and have no problems with two 13.5k Dometic on 30A. Yes, we do shut down the rear AC when we run the micro and we do have the water heater on gas, but we have a residential fridge, a 32" TV and all the other normal stuff. We have NOT tripped a ckt breaker once.

NO, YOU read it again. I see nothing in his post about running his RV on 30 amp service. YOU made the statement about your RV on 30 amp service and I was just letting him know, that almost ALL RV's cannot run 2 AC units on 30 amp service especially his. I will bet if I look at your 50 to 30 adapter, it is burnt and corroded (30 amp side) from the excess amp draw caused by what you are doing. Doug
Sorry Doug, but I hold a Journeyman Electrician license and I will guarantee you my dogbone is NOT burnt or corroded. I know what my system is doing at all times and with BOTH 13.5 Dometic AC's running, even when they both have a compressor start at the same time, it does NOT exceed 30A.

Here is his post I referred to, that you say did NOT exist...
TexasRedNeck wrote:
Regarding the 30 vs 50 amp, I will use 50 amp sites until the fall and hope that 30 amp will run the 15K unit in the main living area and be enough without cranking up the second AC. I think the 15k AC pulls about 17A at start up if I recall correctly.

You are correct, but he did not state that in his first post. Curious, when did being a Journeyman Electrician qualify them as HVAC experts???? IF both 13.5k Dometic Compressors start at the same time you will easily EXCEED 30 amps. The start amps on each compressor is about 16 to 18 amps for a few seconds. And, what other 120 appliances do you have running? The ruuning amps of a Dometic 13.5k on HI COOL is about 14 amps at 95 degrees. 13 amps at 85 degrees. Your RV refer pulls 2.6 for a 2 door to 3.5 for a 4 door. The Power Converter pulls 1 to 3 amps depending on DC load. With both AC's running in 95 degree ambient you are pulling 28 amps. On 30 amp circuit, you do NOT have much extra to run anything else on. Doug
MEXICOWANDERER
Explorer
Aug 08, 2013
Running THREE 15K units 150' from the Caribbean in Quintana Roo, I learned a few things. If I restarted all three from an ambient temperature of say 90F and humidity of 70% one-then-two-then-all would freeze up.

If I started one, circulated air throughout the 40' bus, let the unit extract water (the temperature only dropped a couple degrees during the first half hour) the single unit would dump several gallons of condensate into the bucket. When the humidity dropped to 50% I started the 2nd AC the temperature AND the humidity would fall. At 45% R/H I started the 3rd AC and had no condenser freeze up at all. When I felt like drying the rig out, when all three units were running I started up a 30 pint dehumidifier. Thank goodness the cabinets and furniture were teak. At night when the temperature dipped I left the dehumidifier run. My Mayan neighbors were astonished. The children would fairly dance with glee beneath the outlets. It was so humid in the summer, clothes would not dry well. Used a bath towel outside and three days later it would still be as damp as when I had used it. Those were the days! Fifteen cents per gallon almost-#3-diesel-fuel!
gotsmart
Explorer
Aug 08, 2013
CyberSanford wrote:
Thanks DougRainer

I was told by my original installer about turning the thermostat back a little. I just thought this ac was built to run and to turn back the temp kinda defeats the purpose of getting it cold inside. But I guess if I have to.
So do you think I had a choice regarding the freeze control device? Did I need to ask for that?
thanks
Mark

I have a 13.5 BTU Coleman 9000 series Non-ducted roof AC (9330A713). Here is a quote from the RV manual:
When the outdoor temperatures drop in the evening to below 75°F, the temperature control should be set midway between WARMER and COOLER. Otherwise the evaporator coil may become iced up and stop cooling. Should icing up occur, it is necessary to turn the air conditioner off for at least 45 minutes to clear the coil of ice. Alternatively, you may turn the selector to the HI FAN position until increased airflow is observed.

I wish there was an easy retrofit to move the controls to a wall unit that has an actual (analog or digital) thermostat in it. Such is life. Someday I will replace it with a unit that also has a dehumidifier in it, like this one, except with more than 11k BTU.
hypoxia
Explorer
Aug 09, 2013
I suggest a duel at sunrise between the Texan & Douggrainer.:B On a more serious note, both are excellent sources of information & we are fortunate to have them here. Personally I would go with two 15K units.
TexasRedNeck
Explorer
Aug 09, 2013
hypoxia wrote:
I suggest a duel at sunrise between the Texan & Douggrainer.:B On a more serious note, both are excellent sources of information & we are fortunate to have them here. Personally I would go with two 15K units.

Succinct and sage advice, me thinks. Am getting a quote to replace the 13.5 with a 15.
djedgar
Explorer
Aug 09, 2013
I am not an HVAC expert, but we have two Dometic Penquin 13.5 units. When we bought the mh, we were told not to run the two a/c units on a 30amp circuit. I didn't realize the heat pump was the same 30amp circuit breaker popped in no time at all.

I won't do that again. Maybe it would have been ok if we didn't have the fridge & water heater running on electric too. I still won't do it. To much of a hassle to get the park to reset things.

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