third ac

[azwiz]

Can you run three 15,000 ac's on 50 amps? (w/micro-air units on each)
Thanks in advance

[Mikendebbie]

I would love to know the true answer to this also.

I don't know the definitive answer - but based on what I have read - I am betting the answer is NO you can not run three 15k ACs on 50 amps...and you can't run three 13.5k ACs on 50 amps either.

Well - don't big motorhomes sometimes have 3 or more ACs?
I have read info an another forum that leads me to believe motorhome ACs are cycled with two running on cool and the others running on fan. Don't know how they do it or if this is not the whole truth.

Also - on this forum I have read about folks who have added a 3rd AC with a dedicated/separate 30 amp cord to plug into the campground power. That makes complete sense to me. However - if you do the dedicated 30 amp power source - what is the plug in the ceiling for up at my current fan/skylight where the 3rd AC would go?

I have also seen info that if the ACs have a soft-start capacitor it may be possible to run multiple 13.5k ACs at once on 30 amp power. However, I don't know if two 13.5 k units would adequately cool a big Monte.

Now - I am just throwing all of these rumors, hearsay, and half truths out there because I know there are some smart dudes here that can clear all of this up for a slow student like me.

[azwiz]

exactly, hopefully someone out there knows the answer for real and not just guessing at it! Like you said, where doe's the wiring go for the third unit by the vent where the third unit would mount? Is there an empty breaker spot?

[jcurtis934]

First, you have 100 amps total from the power source into the montana or two hot legs each at 50 amps. That is why a lot of us never hook up to a 30 amp pedestal at a campground...30 versus 100 amps. Some class a rigs had load shedding control circuits that determined what devices had priority over all other loads. The soft start devices now available eliminate that high in rush current that normally happens when an a.c. is allowed to come on as it normally would. So could you run three a.c. units off 100 amps...yes...unless you are also running high current load devices like microwaves, etc at the same time. That is my cut at your question.

[Charlie 3931fb]

We were camping about a year ago or so in New Mexico. Wife and I was doing our walking around and we saw a couple pull in to the site across from us. When he hooked up his power lines he had 2 cords that he pulled. I went over and asked him why the 2 power cords and he told me it was because he had 3 air con's and in that desert heat he wanted to use all 3. I forgot what make trailer (5th Wheel) he was in but it did have full body paint. Think it was 45 foot long because it was a 3 axle 5th wheeler.

To answer your question I just dont know. Was told that I can add a 3rd air into my systems. But with the 2 we have in here you can hang meat in this coach...LOL


Charlie

[DQDick]

If you use the wiring in the ceiling you will only be able to run two at a time. The wiring goes to a switch that will only allow, in our case, the third AC to run if the bedroom is off. Electric draw is not the only reason for this. Keystone only installs just enough supply vents for two AC's, a third ducted unit running at the same time would need a lot more supply vents. To eliminate any concerns we installed our third AC with it's own breaker box and power supply and made it a non-ducted unit. We spend most of our time in either NM or KS so we fequently have to have our awnings in due to wind and deal with high heat and, in KS, high humidity. The third unit was a must for us.

[steiny93]

Originally Posted by DQDick

If you use the wiring in the ceiling you will only be able to run two at a time. The wiring goes to a switch that will only allow, in our case, the third AC to run if the bedroom is off. Electric draw is not the only reason for this. Keystone only installs just enough supply vents for two AC's, a third ducted unit running at the same time would need a lot more supply vents. To eliminate any concerns we installed our third AC with it's own breaker box and power supply and made it a non-ducted unit. We spend most of our time in either NM or KS so we fequently have to have our awnings in due to wind and deal with high heat and, in KS, high humidity. The third unit was a must for us.

DQDick,
If one orders factory 3 ac units don't they come with a power management solution included? Power management then handling the compressor starting issue?

I thought that is how they solved the issue as some of the other manufacturers do. For example our last Cyclone handled the issue in that manner (power management for just the ac units which enabled 50amp service to be enough for shore and generator)

[AZ Traveler]

Steiny,

The third factory air is just being introduced by Montana in 2021 rigs, we have little knowledge on how it is set up.

[steiny93]

Originally Posted by AZ Traveler

Steiny,

The third factory air is just being introduced by Montana in 2021 rigs, we have little knowledge on how it is set up.

ahhh, I was under the impression that the 3rd ac unit had been a factory available option in Montana for a while now.

[DQDick]

No, it will be interesting to see what changes they've made.

[mtlakejim]

We have a third A/C that is run DIRECTLY to the 20Amp 110 plug (NOT the 30 amp but rather the one you plug outside lights into) on the campground power pole. Completely separate from the 50 amp cord. That allows us to easily run all three with no issues. With the same setup we can run two A/C units (one in the ceiling and one independent at a 30 amp site! That's a major advantage and allows us to use a lot of sites that we would have had to pass on with our 42' rig in the summer.


My recommendation would be to run your third A/C power totally independent even if you have a prewired ceiling. It is easy enough to trace the wire down and separate it from the rest of the coach. Then simply install a power receptacle for a 110 volt extension cord on the side of your unit (similar to the 50 amp but smaller of course). I do highly recommend a heavy duty extension cord and perhaps even a twist lock style. It takes just a little more work but as suggested here there are a LOT of advantages and really no negatives.


Currently our third unit is a portable from Walmart BUT we will be installing a third in the ceiling just like DQDick very soon. Like Dick we will install it in the kitchen vent hole but run the power completely independent (I don't think ours has the location pre wired like some units). That location does NOT have ducting to the other units and therefore the unit will be a direct dump. But considering the central location that is fine.


We are stuck serving a 5 year sentence till retirement in the SE New Mexico desert. Ground zero for A/C testing!! NO SHADE! Three A/Cs are mandatory and for the sake of our puppy they must be reliable. You get 20F below ambient with 2 and the portable gives us another 5F. We have a Tempstick which graphs both temp and humidity plus it sends text alarms if temp gets too high. Since the third A/C is independent of the camper wiring it also serves as a fail safe to protect our pup. It would take a full power failure of the campground pole for us to not have at least one A/C.


I will also state that adding reflective material (similar to what you use for car windshield covers) available at Lowes in good sized rolls, makes a MAJOR difference if you don't have any shade! In particular, any model with the front cap "windshield" needs to be covered and perhaps even insulated. To me that was the dumbest thing Thor ever did!


Adding insulation anywhere else you can will certainly help as well. We are all ears if someone has a good way to insulate the slide outs. Since we are stuck in one place for a few years, I am considering taping down some Styrofoam board insulation up there (cut clean and camouflaged of course).

[steiny93]

Originally Posted by mtlakejim

We have a third A/C that is run DIRECTLY to the 20Amp 110 plug (NOT the 30 amp but rather the one you plug outside lights into) on the campground power pole. Completely separate from the 50 amp cord. That allows us to easily run all three with no issues. With the same setup we can run two A/C units (one in the ceiling and one independent at a 30 amp site! That's a major advantage and allows us to use a lot of sites that we would have had to pass on with our 42' rig in the summer.


My recommendation would be to run your third A/C power totally independent even if you have a prewired ceiling. It is easy enough to trace the wire down and separate it from the rest of the coach. Then simply install a power receptacle for a 110 volt extension cord on the side of your unit (similar to the 50 amp but smaller of course). I do highly recommend a heavy duty extension cord and perhaps even a twist lock style. It takes just a little more work but as suggested here there are a LOT of advantages and really no negatives.


Currently our third unit is a portable from Walmart BUT we will be installing a third in the ceiling just like DQDick very soon. Like Dick we will install it in the kitchen vent hole but run the power completely independent (I don't think ours has the location pre wired like some units). That location does NOT have ducting to the other units and therefore the unit will be a direct dump. But considering the central location that is fine.


We are stuck serving a 5 year sentence till retirement in the SE New Mexico desert. Ground zero for A/C testing!! NO SHADE! Three A/Cs are mandatory and for the sake of our puppy they must be reliable. You get 20F below ambient with 2 and the portable gives us another 5F. We have a Tempstick which graphs both temp and humidity plus it sends text alarms if temp gets too high. Since the third A/C is independent of the camper wiring it also serves as a fail safe to protect our pup. It would take a full power failure of the campground pole for us to not have at least one A/C.


I will also state that adding reflective material (similar to what you use for car windshield covers) available at Lowes in good sized rolls, makes a MAJOR difference if you don't have any shade! In particular, any model with the front cap "windshield" needs to be covered and perhaps even insulated. To me that was the dumbest thing Thor ever did!


Adding insulation anywhere else you can will certainly help as well. We are all ears if someone has a good way to insulate the slide outs. Since we are stuck in one place for a few years, I am considering taping down some Styrofoam board insulation up there (cut clean and camouflaged of course).

The negative with separate power for fixed ac is that it doesn't meet RIVA (basically you can't have dual power sources for hardwired). It is a great way to maximize the power you can pull from a pedestal however.

[mtlakejim]

Originally Posted by steiny93

The negative with separate power for fixed ac is that it doesn't meet RIVA (basically you can't have dual power sources for hardwired). It is a great way to maximize the power you can pull from a pedestal however.

And what legal power does RVIA hold to enforce anything I do with my own coach after I buy it? They are strictly an advisory council to manufactures and have no legal authority to enforce codes. Much less tell owners what mods then can or can't do.


As far as I know there are no government codes that would keep you from using all the available power at the pedestal. They would have to stop people from plugging in lights, grills and fans if that were the case. Additionally if two power sources were illegal then what about solar at the same time your hooked up or using a generator?


Besides they have had wishbone cords that got you extra juice for years. They only stopped working when they started requiring GFI plug ins on the pedestals.

[mtlakejim]

Steve Wagnon posted a great video of the A/C duct work he did on the Facebook 380/381 page. Turns out that if you calculate the total cubic Feet minute of air thru the both the returns and vents of our model Keystone only put about 1/2 the required venting (400CFM) capacity that is needed for just one A/C. FYI a 13,500 dometic is capable of moving about 750cfm!


Steven doubled his vents on the ductwork and is now able to get over 20F under ambient with just one A/C. We can barely get that with both of our units using the factory vents!!! Not only that but he reports that the fan sounds like it is not working as hard.

[jetskier]

I can run all three ACs off a single 50a service. It's possible, but it requires some electrical know how since the panel is maxed out for breakers. I didn't do it this way, but If you never plan on a washer/dryer, you can repurpose one of those breakers for the third ac. You need to pull the 3rd AC feed out of the power share switches in the basement wire abiss. It's shared with the front AC.

[beeje]

My ? is why would you want, or need a 3rd a/c in the first place. I don't get it. We spent 2 weeks in the myrtle beach area last year and it was ridiculously hot. Like 95+ at 7am with 110 heat index.

Our main a/c did fine. Never even turned on the BR a/c.

That trip taught us that if we need that much a/c, we are not going there, and will go north in the summer.

[mtlakejim]

Originally Posted by beeje

My ? is why would you want, or need a 3rd a/c in the first place. I don't get it. We spent 2 weeks in the myrtle beach area last year and it was ridiculously hot. Like 95+ at 7am with 110 heat index.

Our main a/c did fine. Never even turned on the BR a/c.

That trip taught us that if we need that much a/c, we are not going there, and will go north in the summer.

Well ok try three months of triple digits and ZERO shade! We could easily go on a vacation and make do for a few days but when you live full time and your stuck due to your job in one place that is litteraly hell on earth then you start to appreciate having enough A/C to keep you comfortable. And then there is a puppy who we must have dependable A/C for. When we retire in 5 years you can bet we will be chasing the better weather across the country!!!!!!!

[Mikendebbie]

Originally Posted by mtlakejim

Steve Wagnon posted a great video of the A/C duct work he did on the Facebook 380/381 page. Turns out that if you calculate the total cubic Feet minute of air thru the both the returns and vents of our model Keystone only put about 1/2 the required venting (400CFM) capacity that is needed for just one A/C. FYI a 13,500 dometic is capable of moving about 750cfm!

Steven doubled his vents on the ductwork and is now able to get over 20F under ambient with just one A/C. We can barely get that with both of our units using the factory vents!!! Not only that but he reports that the fan sounds like it is not working as hard.

Jim - Can you ask Steve to post his info here? I don’t do Facebook/Twitter/instagram or any of those things and I never will. I build their data centers but I do not use their product. Ask him to put it here!

[beeje]

Originally Posted by mtlakejim

Well ok try three months of triple digits and ZERO shade! We could easily go on a vacation and make do for a few days but when you live full time and your stuck due to your job in one place that is litteraly hell on earth then you start to appreciate having enough A/C to keep you comfortable. And then there is a puppy who we must have dependable A/C for. When we retire in 5 years you can bet we will be chasing the better weather across the country!!!!!!!

I see your dilemma. There are campgrounds everywhere it's not possible for you to move to one that's wooded at least somewhat. ?

[jeffba]

Originally Posted by beeje

I see your dilemma. There are campgrounds everywhere it's not possible for you to move to one that's wooded at least somewhat. ?

Trees in New Mexico desert.