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Old 09-10-2018, 08:07 PM   #1
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Air conditioner at 5000 feet above sea level

So we have a 38el in Tombstone AZ at 5000 feet. The unit is 1 year old. With the two zone 1 air conditioners it cannot hold 72 degrees. High today was 92 degrees and sunny. The bedroom temp is below set temp of 72 with the zone 1 units degrees so it never comes on. I have to set it artificially low to get it to come on and get living room temp to 72 degrees. Wondering why the two main ACs cannot cool? Is it the altitude? Anyone else have this issue? Seemed to work fine in Virginia near sea level.
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Old 09-10-2018, 08:14 PM   #2
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Altitude has nothing to do with it . i run my AC from elevations of 6600' and above . These RV's are solar collectors and get hot inside . Reflextix on most all windows helps.
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Old 09-10-2018, 09:43 PM   #3
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Hi,

A number of posts here and elsewhere have said that twenty degrees below ambient outside temperature is about all you can expect from RV air conditioners.

FWIW.

Rich Phillips
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Old 09-10-2018, 09:52 PM   #4
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Thanks for the replies. Sounds like I can't expect much more.
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Old 09-11-2018, 01:24 PM   #5
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In the low humidity of the desert why do you want the A/C on 72 degrees? It overworks the A/C in high temps for no good purpose. Increase the temperature to 75 degrees and it won't tax the A/C quite so much.
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Old 09-11-2018, 01:26 PM   #6
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Quote:
Originally Posted by mwdilday View Post
So we have a 38el in Tombstone AZ at 5000 feet. The unit is 1 year old. With the two zone 1 air conditioners it cannot hold 72 degrees. High today was 92 degrees and sunny. The bedroom temp is below set temp of 72 with the zone 1 units degrees so it never comes on. I have to set it artificially low to get it to come on and get living room temp to 72 degrees. Wondering why the two main ACs cannot cool? Is it the altitude? Anyone else have this issue? Seemed to work fine in Virginia near sea level.
If I understand you correctly, you're saying that one AC is running its heart out trying to cool a large space, and the thermostat for the second unit, for the bedroom, must be set artificially low to get it to run at all.

If that's the case, it appears that the living-room unit is sending too much cool air to the bedroom. It's attempting to cool the entire coach, while the bedroom unit is not kicking on to do it's share of the work.

Several things can account for this.
  • incorrectly installed AC ducting may be directing air from the living-room AC to the bedroom. Close the door to the bedroom; run only the living-room AC; check the bedroom vents to see if air is coming from the living-room unit into the bedroom. There may be a small amount of crossover from one to the other, but the living-room unit should not be pumping cold air to the bedroom if the bedroom has it's own system. If the systems are not isolated as they should be, consult with the dealer and manufacturer.
  • The bedroom AC thermostat is poorly located so that that it's sensing cooled air drifting in from the living-room and not triggering the bedroom unit to run. Close the bedroom door. Consider relocating that thermostat to a warmer location out of this draft.
  • One of the thermostats may be faulty. Try running the bedroom AC only and see how it performs in the bedroom with the bedroom door closed.

Multi-zone systems can be tricky to balance, but one way to really help with this is to physically isolate the zones so that air does not mix from one to the other. Some experimentation may improve the performance of your two-zone systems.
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Old 09-11-2018, 01:31 PM   #7
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p.s.
Dry AZ air is a boon to air conditioning. The lower the humidity, the easier it is to cool the air, and the less likely it is that the systems will freeze-up. Altitude has no significant effect on AC.

In fact, in the dry mountain west, it's possible to cool an entire home with a "swamp cooler" - an evaporative cooler that relies on the cooling potential of water sprayed on a heat exchanger with a fan blowing over it.

Move your RV to Georgia and then you'll really struggle keeping it cool!
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Old 09-11-2018, 01:36 PM   #8
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Yep our house is at 7,000 and we often camp in the mountains close to 10,000 feet and usually it can get it about 15 degrees cooler than what it is outside. (But it's rare to need to use the A/C as it's usually 60's and 70's even in the summer...which is why we see so many RVs from Texas, New Mexico, Arizona, and Florida here!! :-)
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Old 09-11-2018, 02:39 PM   #9
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A/C Helper

When we travel during warmer temp's we bring along out Wind Tunnel fan. The fan moves the air around and help the A/C cools things down and keep it cool. I have also found on those nights when you don't need A/C you can open a roof vent and allow the air to flow through the RV from one end to the other which keeps cool.
When sitting outside the Wind Tunnel helps to keep us cool and blow the bugs away. It was worth the $30.
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Old 09-11-2018, 06:34 PM   #10
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Having designed havoc systems for 40 or so year I can say that Altitude does in fact have an impact on capacity. The smaller the condensing coil the more you have to derate the capacity so the exact number depends on the equipment but it is a safe bet the rv units, that utilize small coils, have a large derate. I could not find manufacturers derate numbers for rv ac units but a Mitsubishi mini split unit, which also has relatively small coils, publishes a .83 derate at 5000 feet. I would say a 17 percent capacity reduction is fairly substantial. My guess is the rv units have a little bit higher derate.
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Old 09-11-2018, 06:46 PM   #11
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My understanding is that CC have a "racetrack" A/C duct system (both A/Cs feed the same duct system) so it is hard to isolate the 2 A/C units. I set the living room A/C at 72 and the bedroom A/C zone at 69 to maintain 72 in the hottest weather. Bathroom vent is about 1/2 closed and one bedroom vent is completely closed with the other bedroom vent just barely open. Seems to keep the temp inside very consistent. Even so, living room is harder to cool with all the windows and the high ceilings. We have dual pane glass and that seems to help a lot.

Good Luck!
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Old 09-11-2018, 06:52 PM   #12
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As a person who lives in my 5'r not too far from you, I can say the UV heating effects in an RV in southern AZ is huge. Like you, when I lived down near the coast (in Southern CA,) my AC units did the job fine, even in the 90+ deg days. Moving to the Southern AZ climate, even at altitude, and the dry air, my RV has a hard time due to the UV solar heating effects out here. Others have stated the specifics as to why the AC's don't function quite as well and I tend to agree with them. But don't worry, with the nights dropping to 57 right now, the much cooler day time temps will be coming down quickly, right about the end of September if history has anything to do with predicting the future.
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Old 09-11-2018, 09:44 PM   #13
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As tomherb said … Cedar Creeks have a race track A/C duct system … one big oval ductwork with two A/C's sitting on it at each end of the camper. There are no isolation panels, so you have to adjust the ceiling diffusers to get maximum cooling effect. Removing each ceiling diffuser and taping up the gap between duct and ceiling panel helped my Silverback a lot. It was blowing cold air into the attic space. Making sure the return ducts are not partly collapsed is another check. If they are, just shove short lengths of 1" PVC pipe inside them to open it back up. Lastly up on the roof, take the bonnet off and remove the 4 lag screws holding the A/C to the roof. Rock the A/C over and be sure the gasket dividing the supply from the return air is correctly in place. Adjust if necessary as you don't want air mixing at this point. Lag it back down and put the bonnet back on.
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