Air Conditioning Capacity question

[Bobby F]

I'm not an A/C person. Hardly ever run it at home, almost never in RV's. But my outside temp just hit 103, and I gave in.

In my older 28' Class C, I have one roof unit, a DuoTherm BriskAir (13,500, I think).

After running it for two hours at 103 and sunny, I'm not dipping much below 86 degrees inside. Shades pulled, windshield covered.

I just need to know - is this normal? Do I have some malfunction I need to chase down, or are RV's just so poorly insulated that 86 is acceptable?

If it's normal, I can live with it - I seldom hit 103 where I go, and I don't use it much anyway. Just want to make sure things are working right.


Thanks!

[jcussen]

Originally Posted by Bobby F

I'm not an A/C person. Hardly ever run it at home, almost never in RV's. But my outside temp just hit 103, and I gave in.

In my older 28' Class C, I have one roof unit, a DuoTherm BriskAir (13,500, I think).

After running it for two hours at 103 and sunny, I'm not dipping much below 86 degrees inside. Shades pulled, windshield covered.

I just need to know - is this normal? Do I have some malfunction I need to chase down, or are RV's just so poorly insulated that 86 is acceptable?

If it's normal, I can live with it - I seldom hit 103 where I go, and I don't use it much anyway. Just want to make sure things are working right.


Thanks!

Not that unusual, I have a new 25 footer with a 15000 btu unit and it struggles when in the direct sun. Reflectix in the windows will help, and parking in the shade will help.

[rogerfromco]

From what I’ve read, you can look for a 15-20 degree reduction from outside temps.

[Solo_RV_Guy]

Originally Posted by Bobby F

I'm not an A/C person. Hardly ever run it at home, almost never in RV's. But my outside temp just hit 103, and I gave in.

In my older 28' Class C, I have one roof unit, a DuoTherm BriskAir (13,500, I think).

After running it for two hours at 103 and sunny, I'm not dipping much below 86 degrees inside. Shades pulled, windshield covered.

I just need to know - is this normal? Do I have some malfunction I need to chase down, or are RV's just so poorly insulated that 86 is acceptable?

If it's normal, I can live with it - I seldom hit 103 where I go, and I don't use it much anyway. Just want to make sure things are working right.


Thanks!

Hi Bobby-

Pretty sure I have 11,000 BTU on top of my Four Winds 23A and eventually it will freeze me out. It seems like the same thing as absorption reefers - you almost can't tell it's working for a long time.

If I start my A/C before it gets above about 80° inside, the unit will hold that temp all day in mostly full sun. And yes, it will even cycle, so I could probably get a couple more degrees out of it.

You have enough heat built up in your RV that it will take hours to exchange it out. If it's still not getting colder...

The A/C techs tell us that if you get a 20° difference between inlet and outlet temps, it's working. If you're not getting that much difference... you could have an air leak and chilled air is escaping, you could have plugged up condenser fins, some other internal component failing. My bet is on getting the heat buildup out of your RV.

Let it run over night and see what you think tomorrow.

[jcussen]

Originally Posted by Solo_RV_Guy

Hi Bobby-

Pretty sure I have 11,000 BTU on top of my Four Winds 23A and eventually it will freeze me out. It seems like the same thing as absorption reefers - you almost can't tell it's working for a long time.

If I start my A/C before it gets above about 80° inside, the unit will hold that temp all day in mostly full sun. And yes, it will even cycle, so I could probably get a couple more degrees out of it.

You have enough heat built up in your RV that it will take hours to exchange it out. If it's still not getting colder...

The A/C techs tell us that if you get a 20° difference between inlet and outlet temps, it's working. If you're not getting that much difference... you could have an air leak and chilled air is escaping, you could have plugged up condenser fins, some other internal component failing. My bet is on getting the heat buildup out of your RV.

Let it run over night and see what you think tomorrow.

Agree, a good ac will lower temps in the coach 20 degrees, but as you say heat built up or heat soak is a problem. so 90 in, 70 out. After a while, might be 80 in, 60 out. Could take a long time, so best not to allow temps to get too high. Outside temp has little to do with it, unless you have ac problems.

[Isaac-1]

It can help to pre-cool the RV during the night or early morning, setting your thermostat for 3-5 degrees cooler than your desired temperature. This way during the day the air conditioner is just trying to maintain a temperature, and not fighting to drop it any.

[aether_one]

Originally Posted by Bobby F

I'm not an A/C person. Hardly ever run it at home, almost never in RV's. But my outside temp just hit 103, and I gave in.

In my older 28' Class C, I have one roof unit, a DuoTherm BriskAir (13,500, I think).

After running it for two hours at 103 and sunny, I'm not dipping much below 86 degrees inside. Shades pulled, windshield covered.

I just need to know - is this normal? Do I have some malfunction I need to chase down, or are RV's just so poorly insulated that 86 is acceptable?

If it's normal, I can live with it - I seldom hit 103 where I go, and I don't use it much anyway. Just want to make sure things are working right.


Thanks!

This is normal. It takes a long time to cool the materials in the RV and they add to the heat load of the external temperature and the sun beating down on the outside.

[TXiceman]

Originally Posted by rogerfromco

From what I’ve read, you can look for a 15-20 degree reduction from outside temps.

I wish this would go away from the internet,

The A/C is working at its maximum when it will have the outlet air temperature 20 degF lower than the inlet temperature. DO NOT measure air temperature with an infrared temp gun. These are to measure the temperature of solid surfaces. You have to use a thermometer and have the air blowing across the element.

Make sure the inlet filter and evaporator coil are clean.

You can help the A/C by putting Reflectix (available at Home Depot or Lowe's in all the windows and outside the windshield.

Ken

[Xmcdog]

If you can reach 86 in two hours there is nothing wrong with your unit.
Turn it on when inside temps reach 75. That way it has a chance.

One day when I am bored I will do a heat load calculation on my RV. I imagine that the heat gain will be very close to the capacity of my a/c. Especially at temps of the 103f range. Yes ambient temps do reduce the efficiency of an air to air system and thus the capacity.

[Podivin]

Originally Posted by rogerfromco

From what I’ve read, you can look for a 15-20 degree reduction from outside temps.

That's not quite accurate. You can expect a 15 - 20 degree drop in temperature comparing the air going in to the air conditioner to that coming out of the air conditioner. The outside temps don't really come in to play in this particular measurement. You may or may not expect a decrease in temp compared to outside temps based on many variables such as are the windows covered, is the RV in direct sun or shade, how much insulation in walls and ceiling - etc.

To answer the OPs question, yep it sounds perfectly normal.

[96 Wideglide]

Originally Posted by TXiceman

Make sure the inlet filter and evaporator coil are clean.

.

Ken

Ken, keeping the evaporator fins clean, is more important than the easier to get to, condenser fins?

[Isaac-1]

Ken, actually IR temperature guns and imagers measure emissivity not temperature, so things that are different colors or have different IR emissions will read differently see this short video for a demonstration.

https://www.youtube.com/watch?v=MBm_DtxXWns

[TXiceman]

Isaac-1, I know, but I did not want to get too deep into the actual method. I am a retired mechanical engineer and spent my career in industrial refrigeration...applied heat transfer and thermodynamics. I did not figure the folks wanted to hear about emissivity of various surfaces.

Ken

[Bobby F]

Thanks, all. Based on what y'all said, I'm satisfied that my unit is working acceptably for what it is.

Just wanted to make sure it wasn't broken. I hate broken stuff. I can live with "they all do that."

And I'll think long and hard before venturing in to places that get over 100 humid degrees again. Yuck. I just end up spending the entire time inside with the A/C, and that's not why I'm out here. Plus, I get annoyed at other people running gennys, so I ought not be doing it myself. Unless it hits 103. Then . . .