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Old 09-01-2021, 02:27 PM   #1
wesaysoracing
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Problems with Cooling - MHC 331RL

2021 Montana high country 331 RL, very little airflow coming out vents only cooled 5° below ambient, open the vent on the front air conditioner and it cool the bedroom down to 70, What can I look for to get more airflow into the rest of the unit
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Old 09-01-2021, 02:44 PM   #2
rhagfo
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There are other cooling AC air flow post. Start by getting a roll of high quality foil duct tape, and seal the vents to the ducts to start with. You may need to seal the inlet side also.
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Old 09-01-2021, 02:57 PM   #3
sourdough
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Sounds like you need to dig into the "guts" as Russ suggested. It's probably still under warranty but between the lost time while it sits at a dealer and the questionable repair you'll have it's probably easier to do it yourself.

By "opening the vent on the front airconditioner" I'm assuming you are referring to the sliding opening or "dump" feature. I am also assuming it is a 13.5k unit (front), 15k rear (living) and you have the "racetrack" (forget the name) duct configuration as I do.

I have never had an issue with air volume or temp coming out of my vents. I did pull them to make sure they were all sealed "just because" and they did a good job sealing mine. I did put adjustable vents in the bedroom (2 out of 4) and one in the bathroom to keep from freezing up top and help the living area on hot days.

Pull the vents; they should all be sealed nicely with foil tape. Sounds like the bedroom A/C is cooling but "cooling it down to 70" still might be a tad underperforming - but you don't state what the outside temp is or any heat mitigation steps you've taken. The front unit does not have access to the plenum if it's the "Whisper Quiet" model (or whatever it's called).
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Old 09-01-2021, 03:02 PM   #4
wesaysoracing
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The rear unit is a whisper quiet 15 K, the bedroom unit is also a 15 K, and yes I was referring to the dump feature, cooling down to 70 in the bedroom is where the thermostat was set, the unit cycles fine, the rear thermostat is set to 70 and there is virtually no airflow coming out of the vents the rear unit runs continuously,
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Old 09-01-2021, 03:10 PM   #5
sourdough
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When you say there is virtually no airflow coming out of the vents, is that ALL of them, all of the time? Both units feed into the same duct system. I can tell when I go from 1 to 2 units because the airflow increases out of all the vents. i have to think one or the other has to be feeding all the vents and maybe one unit is blocked or ?? Is that what's happening? If the bedroom AC is blowing out the dump it will be blowing out the vents unless there's a blockage somewhere. If that were the case the living area unit should be blowing from the other direction.... I'm not really sure how you get no air out of any of the ducting from either A/C unless they just aren't connected to the ducts (both of them) in some way.....and that would be a dealer issue for me.
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Old 09-01-2021, 04:01 PM   #6
jsb5717
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Have you also checked the return vents in the living room to see if those ducts are collapsed? There was quite a bit of talk about those a couple years ago. It's possible that the AC isn't able to pull enough air into itself in order to provide adequate air flow back into the living space. I was able to open mine up with 1 1/2" PVC/ABS pipe as was recommended at that time. It helped...some. You also have to make sure that the black foam filters in the return vents are kept clean. That also helps.

All of that said and I can commiserate with you that our rear AC (the only AC we currently have) woefully underperforms. Even if it's only 85-90 deg. outside the coach can't cool down below 79-80 deg. We do have a 2nd AC being installed in a couple weeks but the performance of the one we have has been relatively pathetic. It seems to be running fine. I've made sure all of the vents are well sealed and not protruding into the ducts. I've pulled the AC cover and gathered all of the various wires, just laying about in the return duct, up out of the way and zip tied to minimize their impact on the return air.

Like you I'm not sure what else to do and am baffled that this unit doesn't put out better cooling than it does.

On yours I would definitely be checking the items stated:

1. Return ducts - are they opened up (I used a borescope to check mine)
2. Return vents - are they clean
3. Air vents - are they well sealed to the duct so that air cannot go into the ceiling
4. Are the air ducts opened up and clear - borescope again

I'm good on all of these things and still underperforming...in my opinion. Perhaps you can gain some improvement.
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Old 09-01-2021, 05:56 PM   #7
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On our MHC331RL, if we keep the dump closed on the front unit, it will assist in cooling the bathroom and rear of the rig. Opening the dump cools the bedroom faster but the rear has a harder time keeping up!
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Old 09-02-2021, 04:43 AM   #8
4Buck
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Make sure the return vents are cut out the same size as the cover. I had to cut all mine out some more then 3inches to make them breath better.
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Old 09-02-2021, 05:48 PM   #9
wesaysoracing
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Thanks for all of the replies, ,it gives me direction to look
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Old 09-03-2021, 03:24 PM   #10
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A very common problem with the actual AC head units is under the shroud at the ceiling. Take off the plastic shrouds and look for the basic foam board divider baffle that is meant to separate the return air intake from the cold air output. Many times this divider moves or falls, which can cause a loss in pressure/flow because the cold air is simply going right back into the warm air return. Very common problem that a youtube search will show and it has happened to both of my units. Use some tape to hold them in place.
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