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Old 07-11-2010, 10:22 PM   #1
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Dual A/C still not enough in 90 degrees, sun, wind, humidity?

Was out camping in Western Minnesota this weekend in 90+ degree temps, full sun, no shade, and wind, and could not keep the traylah cool with both A/Cs blowing. Rear A/C was keeping the bedroom cool but front part of the trailer was still 84 degrees.

Is this is as good as it gets or do I have an A/C problem? Front A/C was blowing on high fan, measured outlet temps in low 70s, inlet in high 80s.
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Old 07-11-2010, 10:40 PM   #2
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Hi,
According to my Coleman ac manual, the ac's are designed to cool the air 15-20 degrees cooler than the incoming air.

"As a general rule, air entering the air conditioner will be cooled about 15 to 20 degrees, depending on the outside temperature and humidity conditions.
For example, if the air entering the return air grilles in the air conditioner is 80'F., the air leaving the discharge grilles in the air conditioner will be 60' to 65'F.
As long as this temperature difference is being maintained between the retum air and discharge air, the air conditioner is operating at its capacity. If the desired inside temperature (normally 80'F.) cannot be maintained, then the heat gain of the R.V. is too great for the capacity of the air conditioner. Parking the vehicle in a shaded area, keeping windows and doors shut and avoiding the use of heat producing appliances in the vehicle will help to reduce the heat gain. When possible, the addition of insulation and tinted glass (especially in uninsulated vans) should
be considered." Coleman 6759 Mach 1.
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Old 07-11-2010, 10:59 PM   #3
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It should be better

In the Texas heat/humidity we stay ahead of the interior heat. We use awnings on both sides and keep the movement in and out the main door to a minimum. Keeping the drapes closed as well. Granted, its a lot smaller unit but its only one AC (Carrier.) Try get shade if possible.....I always plan for that and get a spot shaded from afternoon sun.
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Old 07-11-2010, 11:21 PM   #4
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Quote:
Originally Posted by Jammer View Post
Was out camping in Western Minnesota this weekend in 90+ degree temps, full sun, no shade, and wind, and could not keep the traylah cool with both A/Cs blowing. Rear A/C was keeping the bedroom cool but front part of the trailer was still 84 degrees.

Is this is as good as it gets or do I have an A/C problem? Front A/C was blowing on high fan, measured outlet temps in low 70s, inlet in high 80s.
Hi, are these two air conditioners controlled manually? Meaning that they each have their own controls on the unit, or are they controlled by a wall thermostat? I have two air conditioners in my house, one window and one portable. Once when running them both at the same time, I had a similar situation. Cold air from one of my air conditioners was telling the other one to cycle because it was cold enough, therefore I was only benefiting from one air conditioner. I had to use a fan to redirect the cold air away for the other unit.

I had a "Mac Tools" truck with two roof air conditioners and they worked fine. But since they were both the same, they would cycle at the same time putting a huge load on my generator. I never bought one but I was told there is a kit you can buy that makes the two air conditioners alternately cycle. Possible that one of your air conditioners has a hard time starting/cycling because you have two, so not putting out correctly. Can you partition the bedroom from the front of your trailer to see if one air conditioer is effecting the other one?
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Old 07-11-2010, 11:24 PM   #5
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i've felt cooler by not running the fan on high. i've read here, that this might result in icing on the condenser but it might be worth a try. most folks in the high heat recommend not letting the heat get too far ahead and cool the trailer down before the heat climbs.

your mileage my vary ;-)
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Old 07-11-2010, 11:25 PM   #6
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Couple of things to check:
  • Think about your bathroom vents and fans. Try closing them. Believe it or not it feels like they suck in hot air when you've got the A/C running at full blast.
  • Filters - the filters on my A/C have to be cleaned at least once a month, more often if the weather is dry & I'm tracking more dust into the A/S. It's amazing how much cooler it gets once you clean those filters. If your stove vent doesn't automatically close when the fan is off, there's more hot air infiltrating. And the Refrigerator vent on the roof can fill with leaves, causing the hot air from the reefer to end up inside instead of disbursing. Check for mud daubers on the side while you're at it. Turn the water heater off too if you're not using it at the moment.
  • Awnings - deploying the streetside awning can make a huge amount of difference. I wish I had the complete set, but I've seen a vintage unit or two with improvised awnings or reflective coverings stuck over windows with suction cups... cutting out thermal gain is what it's all about. You could even use a clothes line and sheets to block sun from the hot side if your awning is facing North. Any kind of shade helps.
  • Are your windows tinted or clear? Reflective tint might help.
  • A fan. I've seen A/C units that have a downdraft pattern. Mine doesn't, so the cool air blows along the ceiling getting warm before it sinks. I have an endless breeze that really circulates the air better than my A/C does alone.
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Old 07-11-2010, 11:35 PM   #7
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jammer

did you check the VOLTAGES to each unit?

there is a specific PROCESS for testing cooling function.

i've forgotten the specifics, but they involve measuring OUTPUT (cool) air temps...

compared to the INPUT (hot) air feed.

when the thermostat is set to the coldest temp.

there is a 'threshold OUTPUT temp differential for normal function.

this eval process has been posted HERE somewhere...

see lew's post #6 in this thread...

http://www.airforums.com/forums/f427...-to-46168.html

and here's a couple more with user reports...

http://www.airforums.com/forums/f427...rlr-24219.html

http://www.airforums.com/forums/f427...ool-33741.html
________

without the specifics, one could simply run EACH unit solo

and measure cold air temps when the thermos are eacg set to 60, 65, 70...

they SHOULD be the same in this regard.

ONE 15,000 btu unit will lower inside temps (of a 34) about 20 degrees in full sun

((with foil placed in the vents/skylight and vista views))

wind does impact this but i've got a CRAPPY door seal...

((check the door seal))

reads like your front ac is SUB par.

cheers
2air'
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Old 07-12-2010, 07:36 AM   #8
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Thanks for the replies. There were some questions, which I'll try to answer.

Quote:
Originally Posted by Melody Ranch View Post
In the Texas heat/humidity we stay ahead of the interior heat. We use awnings on both sides and keep the movement in and out the main door to a minimum. Keeping the drapes closed as well. Granted, its a lot smaller unit but its only one AC (Carrier.) Try get shade if possible.....I always plan for that and get a spot shaded from afternoon sun.
We were at the Lac Qui Parle state park upper campground, which was built in the last few years. There was no shade at any of the sites.

Due to the high winds, I couldn't use the awnings except for the two smallest.

Quote:
Originally Posted by ROBERTSUNRUS View Post
Hi, are these two air conditioners controlled manually? Meaning that they each have their own controls on the unit, or are they controlled by a wall thermostat? I have two air conditioners in my house, one window and one portable. Once when running them both at the same time, I had a similar situation. Cold air from one of my air conditioners was telling the other one to cycle because it was cold enough, therefore I was only benefiting from one air conditioner. I had to use a fan to redirect the cold air away for the other unit.
They use the Dometic control system which is all integrated and has separate temperature sensors for each area and a master control. The front unit ran constantly and the rear unit cycled on and off since the bedroom area was cool enough. We had hookups, 50A service, so there was no problem with starting.


Quote:
Originally Posted by richinny View Post
i've felt cooler by not running the fan on high. i've read here, that this might result in icing on the condenser but it might be worth a try. most folks in the high heat recommend not letting the heat get too far ahead and cool the trailer down before the heat climbs.
I had the fan on auto. The front unit was running on high fan and the rear unit on low fan.

Quote:
Originally Posted by Foiled Again View Post
Think about your bathroom vents and fans. Try closing them. Believe it or not it feels like they suck in hot air when you've got the A/C running at full blast.
The fantastic fan and bathroom fan vents were both shut.

Quote:
  • Filters - the filters on my A/C have to be cleaned at least once a month, more often if the weather is dry & I'm tracking more dust into the A/S. It's amazing how much cooler it gets once you clean those filters.
I did pull a filter and it was clean. I've hardly used the A/C since the unit was new.

Quote:
  • If your stove vent doesn't automatically close when the fan is off, there's more hot air infiltrating. And the Refrigerator vent on the roof can fill with leaves, causing the hot air from the reefer to end up inside instead of disbursing. Check for mud daubers on the side while you're at it. Turn the water heater off too if you're not using it at the moment.
Checked stove vent visually and it was shut. The fridge has been performing well but I'll check it. The water heater was running on electric that day.

Quote:
  • Awnings - deploying the streetside awning can make a huge amount of difference. I wish I had the complete set, but I've seen a vintage unit or two with improvised awnings or reflective coverings stuck over windows with suction cups... cutting out thermal gain is what it's all about. You could even use a clothes line and sheets to block sun from the hot side if your awning is facing North. Any kind of shade helps.
The sticky wicket on this particular day was that the wind was too strong to allow use of the awnings. I'd tried to put out the streetside awning, which is about 3'x12', and the wind blew one support arm back to the side wall of the traylah, and I figured I better stow it. Using the curbside awning was out of the question.

Quote:
  • Are your windows tinted or clear? Reflective tint might help.
There's the factory tint. I had blinds shut.
Quote:
  • A fan. I've seen A/C units that have a downdraft pattern. Mine doesn't, so the cool air blows along the ceiling getting warm before it sinks. I have an endless breeze that really circulates the air better than my A/C does alone.
I've thought about a fan to blow the air from the bedroom forward, to take better advantage of the rear air. Doesn't seem like it should be necessary though.

Quote:
Originally Posted by 2airishuman View Post
jammer

did you check the VOLTAGES to each unit?
Yes. I had 50 amp service, and the voltages were reliably at 120-130 volts all day.

Quote:

ONE 15,000 btu unit will lower inside temps (of a 34) about 20 degrees in full sun

((with foil placed in the vents/skylight and vista views))

wind does impact this but i've got a CRAPPY door seal...

((check the door seal))

reads like your front ac is SUB par.

cheers
2air'
I believe my units are 13,500 btu. I don't have foil up.

I'll go through the steps on the other thread.
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Old 07-12-2010, 07:45 AM   #9
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I am seeing about a 10-11* temperature difference from the front unit.

There are some odd noises at times and I thought there might be a damper in there or something to prevent frost but now wonder if there isn't an object blocking airflow over part of the coil. Another item for the warranty list, I guess.
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Old 07-12-2010, 07:52 AM   #10
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If you find the A/Cs are operating correctly, I'd put a fan in the bedroom blowing air toward the front of the camper. First, it'll move some of the cool air from the rear unit to the front of the camper, helping there, and second, the moving air will make it seem cooler inside.
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Old 07-12-2010, 08:57 AM   #11
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Quote:
Originally Posted by Jammer View Post
...I had the fan on auto. The front unit was running on high fan and the rear unit on low fan...

...I believe my units are 13,500 btu. I don't have foil up...
4 some reason in some conditions (high humidity) these units work better NOT using the auto setting initially...

starting with fan on HIGH until cooled, then switching to auto, often works better.

as i recall the icing/defrost cycle functions better or some such thing.

several of us have reported and discussed in some of the other a/c threads.
________

2x13.5 gotcha, that's gonna be a small part of the issue but SHOULD still show 20 degrees diff on each unit.

should not NEED bubble foil with 2 a/c units (unless you've got 2 skylights)

good idea to check for blockage; icing can sure do that too...

cheers
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Old 07-12-2010, 09:14 AM   #12
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Our AC never really cooled well and never really got rid of the humidity. One day I went up top, removed the cover to check things out and found the split cover around the evaporator not snapped together on one corner. That allowed it to always suck in outside humid air instead of recirculating inside air. They have only 2 screws on either side of the fan shaft and plastic snaps for the rest. I solved this by installing screws around the whole thing so it's tight all around. Next was inside the traller and drop the air cover and notice the one inch gap between the outlet duct that doesn't allow all the cold air to be pushed out in the trailer. Instead the blower fan would actually pull back some of the air and create a loop. I solved this by filling the gap with some vinyl sheet and some silicone to stick it in place. You could just use a little aluminum flashing, I just didn't have any in hand. All the work took an hour or two and overnight for the silicone to stick. Results were great. When starting the unit, inside trailer temp was 90, outlet temp was 52 air was dry and not a problem again. I left it on 80 in my driveway for a month in our humid 100 degree NC heat and it stayed dry and at temperature. It would never do this before. We are on an extented trip around the country, currently in Manitou Springs CO. And the first time we haven't needed AC in the summer...
Hope this helps some of you but it's worth getting on your roof and popping the cover and checking. I have the Dometic 13,500 unit (2007 27fb classic)
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Old 07-12-2010, 10:04 AM   #13
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Thanks for all the advice.

Trying to decide now whether to have the dealer look at it (I have to take it in for the second round of warranty matters anyway; they had to order parts and left a few things undone the first time) or climb up there myself.

I am thinking of building some sort of permanent scaffold in my storage shed to provide access in this sort of situation. I assume that pulling the outer shell off the penguin is not a mere ladder job.
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Old 07-12-2010, 10:45 AM   #14
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once ON the roof, removing or installing the shroud is easy and a 1 person task.

it can be LIFTED and transferred easily to a scrap of carpet topside.

be careful around the skylights, they are fragile even when NOT banged on.

along with inspecting, cleaning the fins/coils occasionally is a good habit.

LOWERING the shroud to ground level takes 2.

stay ON the ribs and off the end caps.

it helps to take ALL the expected tools up in 1 trip,

or have a go'fer on the ground.

cheers
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