We bought our 2024 Montana 3941FO new last fall. We are in Houston and it’s not hot yet, only in the 90s but our 3 AC unit isn’t keeping cool. Especially the kitchen and living, bedroom does ok. Current 87 on the thermostat, 81 mid level of the fridge. The air is coming out cold and we just changed filters. Is this common? Our first Montana and it’s going to be a tough summer if she can’t handle May temps.
It’s not hot YET
- Thread starter arose304
- Start date
RMcNeal
Senior Member
It should be able to keep up. I'd check the duct work for any collapsed sections and check and retape the opening around the vents and returns to make sure you're not cooling the attic space. If you have a temp gun, check the actual temperature coming out of the vents. It should be at least 20-30 degrees colder than ambient outside temp.
Bourbon County
Senior Member
RV LIFE Pro
First thing to check is to see if the ACs are actually removing heat. A temp gun isn't the best choice for this, they are made to read surface temps, not air temps. I prefer a digital BBQ thermometer. Stick the probe in a supply vent closest to the unit, next stick the probe into the return. When you check the return, remove the grille and filter and stick the probe into the duct as far as possible without touching the insulation. Record your measurements and repeat with the other 2 units. If the units have been running for 15 minutes or more, you should see between 18-22 degree temperature differences between supply and returns. If you are seeing acceptable temp differences, this is a pretty good indication the ACs are doing their job.
If the ACs are doing their jobs, the issue is likely in the air distribution. Using your BBQ thermometer, walk around the camper spot checking temps in different areas. Are some areas abnormally warmer or cooler than others? A good rule of thumb is anything more than +/- 2 degrees. A usual suspect area is the bathroom, it's a small room and not occupied for very long periods of time usually. I see yours has a sliding door that may or may not be left open; those of us with the infamous pivot doors it's not optional to leave them open. Remove the diffuser (grille) on the bathroom vent and using masking tape, cover the opening. Start by punching or slicing some small holes in the masking tape. I believe you'll find it takes very little air supply to that room, and any visits that take some time the exhaust fan is likely running anyway. Don't be concerned, this is just an experiment, we'll address it later. If you find spots that are abnormally warmer than others, remove the celling diffusers in that area and just leave the holes open. Some just snap into a trim ring, others have a couple of screws; either case it's very easy. It won't change quickly, may take a couple of hours to notice any difference. Go back through and check temps in the same locations and compare to original ones.
If you have anything to check it with, check the humidity also. I'm sure living in Houston, you are painfully aware of humidity and high dew points. My experience is that RV air conditioners do a really good job of removing humidity. Partially because the total air flow of the blower is a little lower than you would normally set a residential unit of that size for.
I found a very sloppy job of cutting away the ceiling panels under the return grilles on my rig. If you can see any of the ceiling material under the trim ring not cut out, it's restricting air flow. I believe Keystone has moved on from their heralded "Blade" system, but normally use some very restrictive supply vents. In a system with that little airflow to begin with, just a square inch or two here and there of restriction can make a big difference in air delivery. Another thing to check for is are there any ceiling supply vents with angled blades pointing towards a return? It's called an air short circuit and simply means a lot of your cooled air is just blowing straight into the return rather than the space. rotate them away as much as possible from the return.
You stated that your rig has 3 units; normally the 3 unit rigs have a non-ducted in the center. Is this your case? If so, that unit should be honking. There are no restrictions on that one.
If you could do these tests and let us know the results there are other options to consider. It would be best if you took the outdoor temperature and humidity levels at same time too.
If the ACs are doing their jobs, the issue is likely in the air distribution. Using your BBQ thermometer, walk around the camper spot checking temps in different areas. Are some areas abnormally warmer or cooler than others? A good rule of thumb is anything more than +/- 2 degrees. A usual suspect area is the bathroom, it's a small room and not occupied for very long periods of time usually. I see yours has a sliding door that may or may not be left open; those of us with the infamous pivot doors it's not optional to leave them open. Remove the diffuser (grille) on the bathroom vent and using masking tape, cover the opening. Start by punching or slicing some small holes in the masking tape. I believe you'll find it takes very little air supply to that room, and any visits that take some time the exhaust fan is likely running anyway. Don't be concerned, this is just an experiment, we'll address it later. If you find spots that are abnormally warmer than others, remove the celling diffusers in that area and just leave the holes open. Some just snap into a trim ring, others have a couple of screws; either case it's very easy. It won't change quickly, may take a couple of hours to notice any difference. Go back through and check temps in the same locations and compare to original ones.
If you have anything to check it with, check the humidity also. I'm sure living in Houston, you are painfully aware of humidity and high dew points. My experience is that RV air conditioners do a really good job of removing humidity. Partially because the total air flow of the blower is a little lower than you would normally set a residential unit of that size for.
I found a very sloppy job of cutting away the ceiling panels under the return grilles on my rig. If you can see any of the ceiling material under the trim ring not cut out, it's restricting air flow. I believe Keystone has moved on from their heralded "Blade" system, but normally use some very restrictive supply vents. In a system with that little airflow to begin with, just a square inch or two here and there of restriction can make a big difference in air delivery. Another thing to check for is are there any ceiling supply vents with angled blades pointing towards a return? It's called an air short circuit and simply means a lot of your cooled air is just blowing straight into the return rather than the space. rotate them away as much as possible from the return.
You stated that your rig has 3 units; normally the 3 unit rigs have a non-ducted in the center. Is this your case? If so, that unit should be honking. There are no restrictions on that one.
If you could do these tests and let us know the results there are other options to consider. It would be best if you took the outdoor temperature and humidity levels at same time too.
We experienced a similar problem. The RV tech told us with the sun hitting the roof, it heated up the Styrofoam insulation underneath it and the air conditioners couldn't cool the ducks down enough to compensate. Once we found www.shaderv.com and bought one, our problem was solved.
If you have 3 acs, are all 3 actually running at same time? Most have a device that cycles them so only 2 actually run at one time. I bypassed mine by actually running a separate power cord to my 3rd unit.
GeologyTek
Advanced Member
I had the 3rd air conditioner added to our 2018 3811MS when I purchased it. After the central "race track" vents blew out an obscene amount of sawdust the center air conditioner started to make a roaring noise. I discovered that the cold air track had been clogged with a massive amount of silver back duct tape. I removed the extra tape, re sealed everything, and made sure it was air tight. I also used a small scope tool to find that several of the ducts were collapsed. You can use 1' sections of 1-1/4" pvc pipe to hold the duct work open if needed. It made a huge difference.
DutchmenSport
Senior Member
Don't over look the reality that your camper has air leaks. The WORST is the furnace return vent under the steps leading to the upper level of your fifth wheel.
Where is the air coming from ... from under the trailer where the colorplast is not sealed tight. The air conditioner is sucking air into the camper, not circulating it as you would expect. It's sucking in hot air from outside from under the camper, through that open return vent and then mixing with already warm air in the camper. Basically, the AC's cannot keep up with all that hot air coming in.
I sealed the underside of my Montana High Country the second year we had it. I used about 15 cans of Foamy insulation "Stuff" and another 15 or 20 tubes of Liquid Nails and various types of calking, in addition to over 200 NEW screws into the frame and the edges of the colorplast.
It made a HUGE difference in the warmth and the function of the heat in the winter. But when Summer rolled around, I was exhilerated when the air conditions (2 of them in a 41 foot fifth wheel) froze us out in 100 degree temperatures!
Air leaks UNDER the trailer, air leaks around pipes, in the floor, around your slide seals, any hole, gap, or crack allows hot air to pull into the camper, all reducing the performance of the the AC's.
If the actual temperature of the AC air flow at the ceiling vent is 20 - 30 degrees less than the outside temperature, then the problem is not the AC, or the duct work, or anything related to the AC. The problem is simply too much hot air entering the camper.
Seal up all those holes and your furnace will function better too, AND in the winter you won't have that cold draft on the floor.
Where is the air coming from ... from under the trailer where the colorplast is not sealed tight. The air conditioner is sucking air into the camper, not circulating it as you would expect. It's sucking in hot air from outside from under the camper, through that open return vent and then mixing with already warm air in the camper. Basically, the AC's cannot keep up with all that hot air coming in.
I sealed the underside of my Montana High Country the second year we had it. I used about 15 cans of Foamy insulation "Stuff" and another 15 or 20 tubes of Liquid Nails and various types of calking, in addition to over 200 NEW screws into the frame and the edges of the colorplast.
It made a HUGE difference in the warmth and the function of the heat in the winter. But when Summer rolled around, I was exhilerated when the air conditions (2 of them in a 41 foot fifth wheel) froze us out in 100 degree temperatures!
Air leaks UNDER the trailer, air leaks around pipes, in the floor, around your slide seals, any hole, gap, or crack allows hot air to pull into the camper, all reducing the performance of the the AC's.
If the actual temperature of the AC air flow at the ceiling vent is 20 - 30 degrees less than the outside temperature, then the problem is not the AC, or the duct work, or anything related to the AC. The problem is simply too much hot air entering the camper.
Seal up all those holes and your furnace will function better too, AND in the winter you won't have that cold draft on the floor.
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