AC Doin' Okay??

[McDonalds]

Okay, it's 100 degrees outside and 80 degrees inside. It's blowing about 63 degrees. Is my air conditioner okay or should I replace it?

[StreamRollin]

As it goes I think you are getting about all the cooling you are going to get. Iv'e heard that 20 degrees lower is about right. I used to have a 21.5 ft Mitchell 5th wheel which I had put a new AC unit on, dont remember what brand it was (I think there are only 2 on the market) but we could get that 5th wheel down well below 70 from 100 degrees if we wanted.
Jim

[Gene]

Once you check on the price of RV A/C, you may decide yours works fine. Some people report they get temps about 20˚ below outside temps. Ours usually does much better than that—at least 30, maybe 35˚.

Things you can do: park under a tree, make it rain, put out awning on sunny side, get Reflectix and put it on roof penetrations and sunny windows inside, clean filters on A/C. You may be need the refrigerant recharged too. Is this the original A/C? If it is 41 years old, it deserves a medal for still working so well. What is the BTU rating for it?—it may be undersized for the trailer.

Gene

[lewster]

Originally Posted by McDonalds

Okay, it's 100 degrees outside and 80 degrees inside. It's blowing about 63 degrees. Is my air conditioner okay or should I replace it?

Manufacturer specification for roof mounted air conditioners is 18*-22*F below inside ambient temperature, this is called 'delta T'. Let your unit run for about 15 minutes. Measure the temp. of the air at the cold air outlet, them measure it again at the return air intake. The temp. differential should fall in the range stated above.

[Gene]

Lew, if I read your post correctly, the 20˚ differential is not between outside and inside temperatures, but between what goes in the A/C and what comes out. Correct?

We start out at 60˚ on the thermostat and that seems to cool a bit faster, and when the temp gets down to around 70˚, we turn up the thermostat.

Gene

[xrvr]

As an experiment my AS was 104 inside. I set the AC on78 on high fan and in an hour it eas 84 inside. This was partial shade. Outside temp was 95. Everything was closed up. I used a tower fan to move air to the warmer side of the trailer. There is usually as much as 4 degrees dif front to back. Exp. done, I have no idea if it would have gotten any cooler, but we keep our house st 82 so I was happy. Remember this camping! Jim

[DKB_SATX]

Originally Posted by CrawfordGene

Lew, if I read your post correctly, the 20˚ differential is not between outside and inside temperatures, but between what goes in the A/C and what comes out. Correct?

We start out at 60˚ on the thermostat and that seems to cool a bit faster, and when the temp gets down to around 70˚, we turn up the thermostat.

Gene

Unless something is wrong with your thermostat, this is just a placebo effect. Unlike automotive AC that sometimes mixes in warmer air when you're at a "medium" setting (on a fully-manual system) or when the air temperature approaches the set point, the roof AC (and usually the one in your house) just has "cooling at max rate" and "compressor off" options. So, while setting a temperature well below what you really want makes you feel like you've sent a message to the machine, the machine just runs at its usual rate until a) it reaches the set point or b) you change the set point to something attainable.

The reason I said "usually" regarding residential AC, there are some newer systems with multiple levels of performance. Some of them are for the multi-head split systems, so the compressor isn't wasting as much energy when just running some of the inside units, but I've seen references to regular AC systems with variable-speed compressor units.

[Phoenix]

A couple of tips:

* Use auto shade screens to block light and lower heat gain through windows.

* Use shade screens over vents and FantasticFans, too.

* Start air conditioner early in the morning before heat starts to build to pre-cool inside surfaces. (Inside air cools quickly; but later in the day, your air conditioner will also be trying to cool down the walls and all contents, too.)

* Gene's suggestion regarding shade will help the most. Very few trees in Arizona, except in the mountains (where it is already cool); but one can tell a significant difference in air conditioner performance, if you can find shade (even partial shade) for your Airstream.

* Don't shower mid-day or hang wet towels inside. Extra humidity decreases same-temperature comfort factor. 80-85 degrees at 5% humidity in Arizona is pleasant, if one is not standing in the sun; compared to 80-85 degrees at 80% in the southeastern US, which is very muggy and uncomfortable (at least for Arizonans).

[perryg114]

When it gets over 100 degrees outside my 4 ton heat pump for the house will just keep the house at about 80 degrees. I should have a 3 ton heat pump on that house according to specs.

The same goes for my 31 ft trailer. It will keep it at about 80 inside when it is 100 outside. There is only so much it can do. The recomendations above about reducing heat load are good ones.

Perry

[Gene]

Originally Posted by DKB_SATX

Unless something is wrong with your thermostat, this is just a placebo effect. Unlike automotive AC that sometimes mixes in warmer air when you're at a "medium" setting (on a fully-manual system) or when the air temperature approaches the set point, the roof AC (and usually the one in your house) just has "cooling at max rate" and "compressor off" options.

I've wondered about that because it doesn't seem to make sense as you say. But if the compressor cycles more frequently as the temp is dropping when you set the temp at 70˚ than when you set it at 60˚, then it would work. It seems to work and hooray for placebos if that is the answer. I could sit in the trailer listening for cycling and do comparisons, but I'm not going to. Maybe I should set the thermostat at 40˚ and see if I can make the entire trailer a refrigerator.

Gene

[vswingfield]

Originally Posted by perryg114

When it gets over 100 degrees outside my 4 ton heat pump for the house will just keep the house at about 80 degrees. I should have a 3 ton heat pump on that house according to specs.


Perry

OK, here's an issue I've never seen on the forums before. When I read the thread, the paragraph above says:

When it gets over 100 degrees outside my 4 ton heat pump for the house will just keep the house at about 80 degrees. I should have a 3 ton heat pump on that house.

The last three words "according to specs." don't appear. It doesn't make sense. When I included the quote in my reply, they appeared and the paragraph made sense.

Using Firefox on Win7. Strange forum behavior.

Back to the original topic, I'm very pleased when I get the inside of my Excella down to 80 when it's 100 outside and in the sun.

[Diesel1]

Originally Posted by McDonalds

Okay, it's 100 degrees outside and 80 degrees inside. It's blowing about 63 degrees. Is my air conditioner okay or should I replace it?

Your A/C sounds like its working as intended. Enjoy it!

[DKB_SATX]

Gene: The modern ones may cycle the compressor before getting down to the set temperature, but I'm guessing that unless it detects something wrong (over- or under-temperature on some sensor, etc) it'll run the compressor full tilt until it gets down to the set point. I'm certain my old one works that way.

[perryg114]

I edited the post so you probably read the post before I added the last little bit of information. I think faster than I type.

Perry

Originally Posted by vswingfield

OK, here's an issue I've never seen on the forums before. When I read the thread, the paragraph above says:

The last three words "according to specs." don't appear. It doesn't make sense. When I included the quote in my reply, they appeared and the paragraph made sense.

Using Firefox on Win7. Strange forum behavior.

Back to the original topic, I'm very pleased when I get the inside of my Excella down to 80 when it's 100 outside and in the sun.

[vswingfield]

Originally Posted by perryg114

I edited the post so you probably read the post before I added the last little bit of information. I think faster than I type.

Perry

That's probably right. I went back a couple of times, but was probably seeing a cached version. It appears correctly now.

[Gene]

Originally Posted by DKB_SATX

Gene: The modern ones may cycle the compressor before getting down to the set temperature, but I'm guessing that unless it detects something wrong (over- or under-temperature on some sensor, etc) it'll run the compressor full tilt until it gets down to the set point. I'm certain my old one works that way.

I don't know why they would cycle the compressor as described, but it could happen. Maybe it is good to rest the compressor periodically for short periods. We have a newer thermostat (2007) which does more things and can be set as low as 40˚. We leave the fan on whenever we are using he A/C and I don't usually notice when the compressor cycles because I've learned to ignore it. Besides, when setting up, no one is sitting in the trailer counting cycles.

So long as we are talking about A/C, several things come to mind—why are RV A/C's noisier than window units at home? Maybe it is because of the confined space with many reflective surfaces. Second, why do they cost so much more than residential window units? And this reminds me of something I read once—horizontal furnaces used in condos and fit in the ceiling, wear out faster than a regular vertical furnace sitting on a floor; does this apply to RV A/C's? Why hasn't anyone designed an RV A/C that sits in the sidewall, like the fridge, and disperses cooled air through some ducts in front, middle and rear?

Gene

[ddstech]

I have a somewhat related question. My parents have a 78 international 31'. The a/c starts out blowing nice and cold but then after about 20 min it starts blowing warm air. What gives?

[billymyers56]

It is 100 today. Air coming out of AC is 54. Temp inside trailer is 76.

[TG Twinkie]

Where is the thermostat set? I believe the recirc fan runs continuously when the unit is on. The compressor kicks in and out based on the ambient temp as compared to the T stat setting.
The thermostat on my AC unit is built into the control panel of the unit. It has a dial with a scale from 1 to 7. 7 being max temp.

[perryg114]

They use to make a kit to covert a standard window unit into an RV roof top unit. The window unit sat on the roof like it would in a window and there were ducts that ran to the inside. I think they are noisyer because the roof vibrates and amplifies the noise. You are also in a confined area where sound reflects.

A compressor should not cycle on and off if it is over 70 degrees in the trailer with the thermostat full cold. If it does then the sense lead on the thermostat is in the wrong place. It can be moved by removing the cover and changing the position of the thin tube coming out of the thermostat. I put mine outside the air box and it solve my short cycling problem. Some thermostats can be tweeked internally to reduce this problem. You don't want the thermostat to see any of the output air.

Perry

Originally Posted by CrawfordGene

I don't know why they would cycle the compressor as described, but it could happen. Maybe it is good to rest the compressor periodically for short periods. We have a newer thermostat (2007) which does more things and can be set as low as 40˚. We leave the fan on whenever we are using he A/C and I don't usually notice when the compressor cycles because I've learned to ignore it. Besides, when setting up, no one is sitting in the trailer counting cycles.

So long as we are talking about A/C, several things come to mind—why are RV A/C's noisier than window units at home? Maybe it is because of the confined space with many reflective surfaces. Second, why do they cost so much more than residential window units? And this reminds me of something I read once—horizontal furnaces used in condos and fit in the ceiling, wear out faster than a regular vertical furnace sitting on a floor; does this apply to RV A/C's? Why hasn't anyone designed an RV A/C that sits in the sidewall, like the fridge, and disperses cooled air through some ducts in front, middle and rear?

Gene