3rd AC

[Rwork]

My 2021 3781RL has two AC units but it does't keep the coach cool enough during the hot summer months in Texas. I was at the dealership yesterday inquiring about adding a 3rd AC unit since it is prewired for it and they told me even if I add the 3rd AC i can only run two at a time. Has anyone else added a 3rd AC? Can you run all three at the same time? It doesn't seem to make since for the factory to pre wire it for a third AC if you can only run two at a time. I can't really shut part of the trailer off (bedroom) because I understand that the air duct is built like a race track and will dump air into the other room anyway. Any help understanding this is greatly apppreciated.

[Ram Montana High Country]

Friends added a third to a 3813MS - there is a load monitor device the prevents over loading the 50A shore power. What AC units do you have Dometic or Coleman?

They can start two and a few minutes later the third, usually works. No other 120v loads on helps.

Coleman may have the SOFT START from the factory which is more likely not to cause over load.

[Carl n Susan]

Montana seems to believe that three ACs are too much for the electrical system and install a load sharing device to limit you to two at a time. Many members have installed a third AC bypassing it or via a separate power cord to the shore power point. Do a Search here for "3rd AC' and you should find a number of Threads on the topic.

[Daryles]

I'm sure you have heard this before and it's not always possible but try to find shade.

Or https://www.shaderv.com/

Also cover the stair vents in the summer (don't forget to uncover them in the winter, these are the returns for your furnace).
You can get magnetic covers for your floor vent at Walmart. Anything to trap your cold cabin air inside.

Tape reflectex to the inside of your basement doors.

Tape reflectex to the inside of your pantry and cabinet exterior walls.

Try to keep the windows shaded.
Here is a window film test I did.
https://www.montanaowners.com/forums...57#post1224357

At the rally I spoke to someone with dark full body paint. They said they had the dealer take the cap off and add more insulation in there. Helped a lot.

[carlrx7]

I believe they moved the load share from the a/c's to the Microwave/Vacuum. Check your circuit breaker panel labels.

I run all three when on 50 amp, no issues. The three Coleman Mach Powersavers only pull 4,200 watts total of the 12,000 available on 50amp service.

[RipNC]

Originally Posted by carlrx7

I believe they moved the load share from the a/c's to the Microwave/Vacuum. Check your circuit breaker panel labels.

I run all three when on 50 amp, no issues. The three Coleman Mach Powersavers only pull 4,200 watts total of the 12,000 available on 50amp service.

They did just the vacuum on our 2021. I'm putting in a 3kw inverter and while noodling thru my wiring I found the load share box and one output goes to a duplex receptacle in the concealed part of the basement. The vac is the only thing plugged in there. I assume the other lead goes to the middle AC. We use a cordless vac so non issue for us.

Also, the Victron inverter I'm installing will provide boost in low power conditions, which may help with the third AC which will be next on my project list...

PS - labeling in our panel is vague and barely legible.

[Rwork]

Thanks, I'll look into this. My breaker panel is not well marked so I will look a little closer at it tomorrow. I talked with an independent RV shop I learned of yesterday and had a talk with him about adding the third AC and he talked like it would work if I didn't have a load sharing device that would alternate which AC would run at any given time. Not sure what this is about. I see that you are in North Texas...mind sharing your city? I live in Bells.

[DQDick]

The first thing you need to consider is that if you add the third unit and it is ducted you'll need to add a number of new supply vents since the number currently in your unit is actually the minimum that Dometic says you should have for two. We added a nonducted unit an wired it to a 30 amp breaker we added to the basement and then ran wire to a 30 amp inlet we added next to the convienence center. We can run all three at once, get the full use out of all three and use both the 30 and 50 amp plugs on the pedestal.

[scuba dude]

I added a third ac to my 2020 3813 wired it direct using dryer breaker since I dont have a dryer and did not tie it into the duct work.I wanted all air to dump out in kitchen and living area and it works great. I can run all three ac if I need to at same time.

[Rwork]

Thanks! I have a washer/dryer connection that I don't use and I will try that.

[scuba dude]

You may check but on my 2020 3813 I pulled out the breaker panel and behind it was a square electrical junction box which the cables for all three ac units ran into. The wire for the middle ac was marked with a piece of black electric tape raped around it. I just unhooked it and hooked it to the dryer breaker and ran new wire from it to wet bay. From wet bay to electric pedistal. Works perfect.

[DavidG425]

We have a 2020 3813MS. There is no load monitoring device that I can find on our coach. Check the back of the installation manuals for the air conditioners that came on your coach. They should show "Mach 15 PS". The PS is for power saver. We replaced the Fantastic Fan with another 15K BTU power saver air conditioner. Everything was prewired. Replace the Fantastic Fan controller on the wall with a thermostat and you're all set. We run all 3 at the same time in the Southern California heat with no problem.

[mootana]

Dear Rwork,
Your 2021 should have Coleman Power Saver AC installed. As long as you install a Coleman Power Saver in the 3rd AC location, there is no need for a power shedding device. The Power Saver ACs pull less then 11 amps.

Any Montana Dealer can contact his Montana Rep and we can provide install instructions.

You can PM me with an email address if you'd like me to send you the install instructions.

Sam

[Randy Auman]

Before adding a third airconditoner check the venting. I found the return air for the rear airconditoner was fully block for one vent and 50% blocked on the other. Also check the vents most all my vents were blocked. There are some good youtube videos showing how to use 1" 1/4 PVC pipe and open up the vents. Adding short 4" pvc pipe to the side of each vent that was blocked increased the air flow at least 50% for my trailer.

[Edd]

Originally Posted by Rwork

My 2021 3781RL has two AC units but it does't keep the coach cool enough during the hot summer months in Texas. I was at the dealership yesterday inquiring about adding a 3rd AC unit since it is prewired for it and they told me even if I add the 3rd AC i can only run two at a time. Has anyone else added a 3rd AC? Can you run all three at the same time? It doesn't seem to make since for the factory to pre wire it for a third AC if you can only run two at a time. I can't really shut part of the trailer off (bedroom) because I understand that the air duct is built like a race track and will dump air into the other room anyway. Any help understanding this is greatly apppreciated.

I added a third A/C [1550 BTU] in the kitchen were the vent used to be. It was already pre wired. The power to the to third A/C went to a switch box to float the third A/C and the bedroom simultaneously behind the circuit breaker panel. I removed the third A/C power from that box and wired it to the dryer circuit breaker. I can run all 3 A/Cs on a 5500 generator or 50 amp service. Trust me when i say it works perfect! Las Vegas 120 degree it was chilly inside. Most of the time we dont even run the living room A/C at all. The third A/C dose not tap into tap into the central venting system it just dumps straight down into the kitchen/living area.