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Old 07-02-2019, 11:50 AM   #1
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Dometic AC barely cools

We've purchased a 2014 Forest River Wildwood which has a single Dometic AC unit & thermostat. We're in Eastern Ontario so hot & humid summers. Last weekend we wanted to use the AC, put it to 19 Celsius, it barely cooled the 30 Celsius outside temperature so we put it as cold as it would go - it was on 13 Celsius for 6 hours and the inside temperature was 23 degrees at its coolest. We've cleaned the filter, ensured the fins are straight etc, all the suggestions. This was with the main intake open and the return open full blast. If we tried closing the main vent to force it to the rest of the trailer, it froze up within an hour and blew ice chunks through the system!

We think possibly 2 issues here:
New modified intake assembly from Dometic?
Freeze-up caused by low freon?
Much appreciated!
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Old 07-02-2019, 12:18 PM   #2
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Did you check the partition between the supply and return to be sure that it was sealed?

Do you have an IR thermometer? If so check the air coming out the supply and see if it's ~9ļC cooler than the return.

Have you looked into the ducting to see if it's open along the path, closed at the ends, and connected to the supply plenum?
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Old 07-02-2019, 12:29 PM   #3
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The difference in temps is well within the parameters of those roof top units. In US degreees , you had 87 outside and 73 inside. That's pretty darn good for one unit. How long is your TT ??
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Old 07-02-2019, 12:42 PM   #4
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We're planning to buy an IR thermometer to measure those temperature variations. It is a long trailer (31ft) so we're also considering we may have to supplement with a 2nd unit...

We'll also check the entire venting path to ensure its closed at each end etc.

Thank you for your suggestions.
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Old 07-03-2019, 03:07 PM   #5
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If the evaporator freezes up, it almost invariable indicates either low air flow, or low refrigerant...possibly both.

If your evap coils are reasonably clean (as well as you can tell without taking the thing apart), and the ceiling vents are all open, the problem is probably not air flow. You might want to check the condenser coil for obstruction also. I look at mine every spring, and it often shows a collection of dust, tree pollen, and general dirt. You can clean it with a garden hose and nuzzles, as it is an outdoor operation. Just tale the plastic hood off (usually four screws) and back flush the coil.

As these units are officially not field serviceable a good A/C tech will be able to install a service valve port, and recharge the unit with the appropriate ozone friendly gas. Most newer units use R-134a, and older ones use R-22, which must be replaced. I use Dupont MO99 also known as R-438A. It is a great and approved replacement gas, as no system changes are needed. And yes, I do have an EPA Universal certification for refrigerants.
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Old 07-03-2019, 04:45 PM   #6
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Awesome info here for those of us struggling with keeping cool in the hot summer sun.

Thanks EPA dude!
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Old 07-05-2019, 01:31 PM   #7
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Your AC unit is only capable of removing so much heat from the air inside the camper. When the heat gain exceeds the ACs capacity the inter temps rise even with the AC running constantly.

The thermostat is actually just an on/off switch. Turning the desired temp lower will not cause the AC to reach any temp faster than if you left it at your actual desired temp.

Since you cannot increase the AC's capacity to remove heat the next solution is to reduce the heat gain in the camper. Parking in a shaded spot will help, IF there is such a spot to be found. Often times there is not, you are at the mercy of the merciless sun.

We live in S Louisiana, heat/humidity capital of the USA. DW and I have two units but typically only run the 2nd one in the bedroom while sleeping. We simply close off that door during the day.

We just recently installed some reflective coated bubble wrap on the inside of the windows in the living area, the skylight in that area and one high side window.

We bought a 4' x 10' roll for $40.00 or so from CW and cut it to fit the top portion of all the windows. We cut them so they aer a "press fit" inside and can be removed and rolled up for storage very easily and simply. They do not fall off while traveling though.

It made a HUGE difference. We immediately felt the temp drop appreciably because it stopped the huge heat gain flowing through the windows.

Before someone says we made it darker, YES, we did, but the interior lights work well. We are in an electrically lit cool space, rather than a naturally lit hot space.

We like choice A better.
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Old 07-05-2019, 01:47 PM   #8
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31ft. That's pretty big for a single air conditioner. As has been stated, you'll probably need some supplemental insulation or a second ac unit to meet your cooling demand.
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Old 07-07-2019, 11:49 AM   #9
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Quote:
Originally Posted by DouglasReid View Post
Your AC unit is only capable of removing so much heat from the air inside the camper. When the heat gain exceeds the ACs capacity the inter temps rise even with the AC running constantly.

The thermostat is actually just an on/off switch. Turning the desired temp lower will not cause the AC to reach any temp faster than if you left it at your actual desired temp.

Since you cannot increase the AC's capacity to remove heat the next solution is to reduce the heat gain in the camper. Parking in a shaded spot will help, IF there is such a spot to be found. Often times there is not, you are at the mercy of the merciless sun.

We live in S Louisiana, heat/humidity capital of the USA. DW and I have two units but typically only run the 2nd one in the bedroom while sleeping. We simply close off that door during the day.

We just recently installed some reflective coated bubble wrap on the inside of the windows in the living area, the skylight in that area and one high side window.

We bought a 4' x 10' roll for $40.00 or so from CW and cut it to fit the top portion of all the windows. We cut them so they aer a "press fit" inside and can be removed and rolled up for storage very easily and simply. They do not fall off while traveling though.

It made a HUGE difference. We immediately felt the temp drop appreciably because it stopped the huge heat gain flowing through the windows.

Before someone says we made it darker, YES, we did, but the interior lights work well. We are in an electrically lit cool space, rather than a naturally lit hot space.

We like choice A better.
Thank you for your helpful comments. This past weekend it was 40 celsius here and we removed the filter in order to allow max air flow, we also keep it very dark but will definitely try the reflective sheets on the windows. We are partially shaded but full sun for 6 or so hours. We're also going to put new tape on the intake to ensure we're not losing air there.
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Old 07-07-2019, 03:50 PM   #10
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Quote:
Originally Posted by suze71 View Post
Thank you for your helpful comments. This past weekend it was 40 celsius here and we removed the filter in order to allow max air flow, we also keep it very dark but will definitely try the reflective sheets on the windows. We are partially shaded but full sun for 6 or so hours. We're also going to put new tape on the intake to ensure we're not losing air there.
You are very welcome.

If I were you I would rethink my decision to remove the filter from the SC. The dust filtered out by the filter can coat the evaporator coils making them MUCH less efficient, decreasing the cooling capacity of your AC, possibly even freezing up the coils.

Better to clean it more often than remove it.
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Old 07-07-2019, 04:08 PM   #11
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Just a suggestion for when anyone is having troubles cooling under extreme conditions.....myself included....

If possible....close the slides. That way you reduce the square footage of your rig to cool. None of these things is really that well insulated compared to a house and RV air conditioner units arenít as efficient as home units.

Smaller space....cooler face 🥶
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Old 07-07-2019, 04:56 PM   #12
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Quote:
Originally Posted by kenandterry View Post
Just a suggestion for when anyone is having troubles cooling under extreme conditions.....myself included....

If possible....close the slides. That way you reduce the square footage of your rig to cool. None of these things is really that well insulated compared to a house and RV air conditioner units arenít as efficient as home units.

Smaller space....cooler face 🥶
That is all true but for us that wold leave us unable to get into our bedroom.

We would also not able to pass more than 4' beyond the side door because we would have to walk on the raised inner edge of the slide outs, which is not recommended by FR.

The Physics is perfect, the Physicals....not so much.

Good Idea though, for those who can do so
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Old 07-07-2019, 08:40 PM   #13
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Ah ok we'll put it back on, we had wanted to establish if the system could cool vs. if it was a faulty unit. We're learning that this is not an exact science whereby you turn it on and it cools the space, many more factors involved. By the end of the summer I'm sure we'll have it downpat lol.
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Old 07-10-2019, 05:18 PM   #14
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Last summer we purchased a 2019 Heritage Glen RK-282. We camped about 6 times with it and liked it very much. This year, not so much. The slide seals are falling apart even though they have been treated and now the AC is on the fritz.


Last summer even though it got really hot out out TT stayed very present in side. But now for some reason the coldest the air coming out of the AC unit gets is 60 degrees, that's it. The AC prob was in the air stream for 30 minutes. I am pretty sure that it should be colder than that. It's not frozen up and there is plenty of air circulation as well. Is this AC unit south on me?
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Old 07-10-2019, 05:49 PM   #15
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Cleaning matters.

I had a used Pop-Up that had an A/C unit in it. I think it was in the 10-13.5K BTU range, Coleman-Mach unit. It would only give me about 10-13 degrees of a delta ... granted a trailer is much hotter when in direct sunlight than ambient would suggest. Either way, when it was 90 F outside, sun beating down, it would be about 80 inside.

When I sold it, I pressure washed the entire unit to clean it up. When I pressure washed the A/C unit, dirt, dust, and grime just poured out of the cooling fins. I mean, a lot of crud came out.

I have a new trailer with a 13.5 BTU A/C. At Moab with 95 ambient and sun beating down to the point it would burn your hand to touch the side of the trailer. I held 68 inside, easy.

I really wonder if my Pop-Up's A/C wasn't just clogged up with too much crap to be efficient ... and the new owner gets 2x the performance out of it.
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Old 07-11-2019, 06:21 PM   #16
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maybe try modding the AC to work better?

Pimp My Coleman Mach 3 AC
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