Questions on Installing Second AC in 2010 3750 - Montana Owners Club

snowhawk2 · 07-28-2010, 05:08 PM

Our 39' 3750 with 5 side outs is a lot of real estate to cool and our 15k AC unit has struggled in 90 plus hot and humid conditions. The bedroom is prewired for a second AC and has the two connector cables already in the ceiling. My question is do we need to install a unit that directly cools into the bedroom or one that ties into the existing duct work? The Duo Therm digital control has two zones and there is a temperature sensor in a birdcage in the bedroom. Either way how does the two AC units integrate with each other to manage air flow and cooling ability?

Thanks so much for your input.

Rich

exav8tr · 07-28-2010, 06:33 PM

We have the direct flow unit in the BR. With both going it cools the whole unit great. At night we just use the BR unit and we stay very cool. It is a little loud but earplugs work wonders. In the evening we sometimes just use the BR unit and put a fan on the stairs to blow air into LR, it is a little quieter this way. I just noticed you have the front living model so I'm not sure what to tell you about that......Good Luck!!!!

lcarter · 07-29-2010, 04:01 AM

We have a stand alone unit second AC in our bedroom. It really helps cool down the trailer. You will have to work on balancing the new unit with the existing one due to the location of the thermostat. Our thermostat is on the landing between the bedroom and the kitchen (closer to the bedroom). This influence temps in the bedroom versus the rear of the trailer. It is quite the advantage to put the rear AC on quick cool and crank up the front AC when you stop for the night when traveling.
LCarter

Clemson1881 · 07-29-2010, 08:04 AM

With your unit being pre-ducted I would recommend connecting the second unit to the ducts. I tried the freeblow style first and quickly discovered you waste a ton of the second unit's cooling capacity by it not being ducted. With your floorplan you would have to leave the doors open through your bath, and the front living area will get no benefit from the second unit. Go ducted.

Clemson1881 · 07-29-2010, 08:16 AM

The two units will blow into the same ducts. You can use either one and distribute air evenly throughout the camper. Or you can run both and double the air forced out of all of your ceiling vents. The two sensors will cycle the compressors on/off to create two separate temp zones in the camper. Or you can set both zones the same. I was able to maintain low 70s at MYRTLE Beach in July with it being in the high 90s. The year before with the same bedroom unit only with a freeblowing ceiling assembly I couldn't keep it cool in the living area. The bedroom would freeze quickly and the front unit would knock off. The back unit would run wide open and struggle. It's all about even air distribution, so both units will be 100% effective. I don't think this is as big of a problem for center aisle coaches like the 3400, but my side aisle trapped my bedroom air. Go ducted. More efficient. More options.

Clemson1881 · 07-29-2010, 08:19 AM

The two units will blow into the same ducts. You can use either one and distribute air evenly throughout the camper. Or you can run both and double the air forced out of all of your ceiling vents. The two sensors will cycle the compressors on/off to create two separate temp zones in the camper. Or you can set both zones the same. I was able to maintain low 70s at MYRTLE Beach in July with it being in the high 90s. The year before with the same bedroom unit only with a freeblowing ceiling assembly I couldn't keep it call in the living area. The bedroom would freeze quickly and the front unit would knock off. The back unit would run wide open and struggle. It's all about even air distribution, so both units will be 100% effective. I don't think this is as big of a problem for center aisle coaches like the 3400, but my side aisle trapped my bedroom air. Go ducted. More efficient. More options.

snowhawk2 · 07-29-2010, 05:05 PM

Hello: Thanks for your feedback and input. I called Keystone today to discuss the advantages and disadvantages of direct vs. ducted. Suffice it to say I wasn't able to get to anyone who could give any meaningful advice. I'm sure they have the answer at Keystone but I didn't have time to keep trying. I called Dometic also and they were no help. So I came home and turned on the computer,and my MOC friends had input that was so much better then the supposed experts. My coach is pre-wired for the second AC so we took the innards of the vent out and the two wires that connect the second air were where they should be. However, after removing the luan side to look for a duct we found a rafter. So we went in the house thinking we would have to go direct. The more we considered it it just didn't make sense that it wouldn't be ducted. So we went back out and three of the sides had clean luan and the fourth didn't. It was a different material so we peeled it back and low and behold, duct work with tape over it. To be sure, I poked a hole in it, turned the air on, and out came cold air. We are excited because 90% of the input we received was to go ducted. Tomorrow I will order the parts.

Any advice on the installatoin or parts needed, is much appreciated.

Happy trails.

mhs4771 · 07-29-2010, 06:08 PM

Just had the low profile Dometic installed on my unit. You need to order three parts, the main unit, the electrical control box, and the quick cool cover. Once installed you just have to reset the thermostat to acknowledge the second zone. You will love it. Stay cool.

smfdva · 08-01-2010, 04:35 PM

Curious, I just had a bid for a low profile unit installed on my Montana 2955RL. It will be ducted using existing wiring, duct work, thermostat, and the dedicated breaker provided. Curious what I should expect the job to cost with all parts and labor? Will post my bid later to not influence discussion.

mhs4771 · 08-02-2010, 06:03 AM

For my 13.5K Penguin Low Profile total cost parts and labor was $1150. Just a side note, I got a quote of $1350 at another place. The higher price was through a Keystone Dealer, I had the work done at an RV Service Center where they do no sales just repairs, installs, and mods.

Hope this helps,

Michelle S.

Lambchop · 08-02-2010, 06:12 AM

My dealer wanted $1270.00 for the unit & $300.00 for labor?

Ridiculous!!

Roy

Clemson1881 · 08-02-2010, 01:54 PM

I paid $900 for a low profile Carrier, ceiling unit, wireless remote control, and installation.

boje · 08-03-2010, 03:24 AM

Snowhawk2-
Does your bedroom have a Fantastic Vent? My unit came with the A/C in the bedroom, and a pre-wired option in the kitchen. I would have to remove the F/V in the kitchen, to add a A/C. I would not be able to tie it to the existing duct work.

Clemson1881 · 08-03-2010, 05:14 AM

My fantastic vent is in the kitchen. Bedroom was a normal vent. I would think on the 3750 they would have it set up to be ducted. If not with that spot being in the center of the unit a freeblow would work better than being up in the bedroom of a side aisle trailer.

Clemson1881 · 08-03-2010, 05:15 AM

My fantastic vent is in the kitchen. Bedroom was a normal vent. I would think on the 3750 they would have it set up to be ducted. If not with that spot being in the center of the unit a freeblow would work better than being up in the bedroom of a side aisle trailer.

smfdva · 08-06-2010, 01:28 PM

Found a few complaints of the Penguin unit (leaks), but I assume a few complaints is normal for one of the best selling units. Any thoughts on brands?

snowhawk2 · 08-16-2010, 03:05 PM

Well thanks for all of your input. This week we purchased a 13500 BTU Dometic, the control board, and the inside ceiling piece for $867 from my local dealer and my friend and I will install this week. The duct work, 110, and cables are in place. I'm looking froward to getting it installed and will post when we test it. With our luck we won't hit warm weather again this season!

snowhawk2 · 08-25-2010, 01:16 AM

I NEED DIP SWITCH CONFIGURING HELP - ZONE 2 NOT RECOGNIZED

Well the second AC is in and it was a pretty straight forward installation with the help of my Buddy Jim who has done many before. It runs fine and having yet had hot weather to really test the capacity with two ACs.

However, the DuoTherm thermostat is not recognizing zone 2. In each control box is a series of dip switches that need to be set properly for the two units to work independently and together, and it's working yet. Now both ACs are in the same zone. No instructions with second unit or with thermostat that will help here. Today I tred the painful task of calling Dometic and waiting on hold for an hour, expecting to get a rookie that won't be of much help, as has happened several times in the past.

Any help from the MOC membership would be greatly appreciated. I'm hoping that someone with a Montana with two AC's can check out their settings which is easy to access behind a little metal door held by one screw. Thanks in advance for your help.

snowhawk2 · 08-29-2010, 09:56 AM

Well the second air conditioner is in and tested today in 90 degree heat and here is an update.

AC, control board, and inside grill $813. Installation free as my buddy and I installed, and he is the brains of that operation. Installation took about 1.5 hours. I called Dometic and they told me how to set the dip switches on both control units, #2 in rear and #5 in front are the only ones that are on. To reset the thermostat so zone 2 would be recognized, all you do is hold the zone and mode button down and at the same time, turn the black power switch to on. When you see FF in the display you are good to go and let go of all switches.

It is 90 degrees today and I'm glad to report that it is 72 in the main area, 71.9 up front, and 74 in the bedroom which has been taking direct sun all day. The good news is that I'm only using med fan at this point. The coach is a million times cooler and no problem keeping up. It will be interesting to see how it handles 100 degrees some day.

At this point the second AC really seems to have done the trick. I guess all long Montanas should really have two ACs. That's it for now and I'll post any updates.

smfdva · 08-30-2010, 04:28 PM

Thanks for the update. Since the season is almost over, it will be a project for next Spring. Now if Hurricane Earl will just skip Virginia since I will be camping with my 5ver at Virginia Beach Oceanfront this weekend! Gotta get the all the trips in we can this year.

You may also like: